bluuebunny/crossref_metadata_2025 huggingface dataset:
Intermittent high glucose enhances apoptosis in human umbilical vein endothelial cells in culture
Authors: Risso A. , Mercuri F. , Quagliaro L. , Damante G. , Ceriello A.
Published: December 2017

To explore the effect of fluctuating glucose on endothelial cells, human umbilical vein endothelial cells were incubated for 14 days in media containing different glucose concentrations: 5 mmol/l, 20 mmol/l, or a daily alternating 5 or 20 mmol/l glucose. Apoptosis was studied by different methods: viability assay, cell cycle analysis, DNA fragmentation, and morphological analysis. Furthermore, the levels of Bcl-2 and Bax, well known proteins involved in apoptosis, were evaluated. Stable high glucose induced apoptosis in human umbilical vein endothelial cells, a phenomenon accompanied by a significant decrease of Bcl-2 and a simultaneous increase of Bax expression. However, apoptosis was enhanced in human umbilical vein endothelial cells exposed to intermittent, rather than constant, high glucose concentration. In this condition, Bcl-2 was not detectable, whereas Bax expression was significantly enhanced. These findings suggest that variability in glycemic control could be more deleterious to endothelial cells than a constant high concentration of glucose.
CaMKIV/Gr is dispensable for spermatogenesis and CREM-regulated transcription in male germ cells
Authors: Blaeser Frank , Toppari Jorma , Heikinheimo Markku , Yan Wei , Wallace Mia , Ho Nga , Chatila Talal A.
Published: December 2017

The calcium/calmodulin-dependent protein kinase type IV/Gr (CaMKIV/Gr) is expressed in male germ cells and spermatids and has been implicated in controlling the differentiation of germ cells into mature spermatozoa. The function of CaMKIV/Gr in spermatogenesis was investigated using CaMKIV/Gr-deficient mice generated by targeted gene disruption. CaMKIV/Gr-deficient males exhibited normal spermatogenesis, and their fertility was similar to that of wild-type littermates. Notwithstanding the function of CaMKIV/Gr as an activator of cAMP response element (CRE)-dependent transcription, mRNA levels of several testis-specific CRE modulator (CREM)-regulated genes were unaltered. These results indicate that CaMKIV/Gr is not essential for spermatogenesis or for CRE-regulated gene transcription in the testis.
Insulin and C-peptide secretion and kinetics in humans: direct and model-based measurements during OGTT
Authors: Tura Andrea , Ludvik Bernhard , Nolan John J. , Pacini Giovanni , Thomaseth Karl
Published: December 2017

To directly evaluate prehepatic secretion of pancreatic hormones during a 3-h oral glucose tolerance test (OGTT), we measured insulin and C-peptide in six healthy control, six obese, and six type 2 diabetic subjects in the femoral artery and hepatic vein by means of the hepatic catheterization technique. Hypersecretion in obesity was confirmed (309 ± 66 nmol in obese vs. 117 ± 22 in control and 79 ± 13 in diabetic subjects, P ≤ 0.01), whereas early phase secretion was impaired in diabetes. We also measured hepatic insulin extraction (higher in diabetic than in control subjects, P = 0.03) and insulin clearance. The measured data were also used to validate a previously proposed mathematical model, developed to quantify prehepatic secretion, hepatic insulin extraction, and insulin clearance during OGTT, when C-peptide and insulin concentrations are systemically measured. We found good correspondence between experimental data and model estimates for prehepatic insulin secretion ( P > 0.3, r 2 = 0.93), whereas estimation of hepatic insulin extraction and insulin clearance needs further investigation for improvement.
Comparison of GH, IGF-I, and testosterone with mRNA of receptors and myostatin in skeletal muscle in older men
Authors: Marcell Taylor J. , Harman S. Mitchell , Urban Randall J. , Metz Daniel D. , Rodgers Buel D. , Blackman Marc R.
Published: December 2017

Growth hormone (GH), insulin-like growth factor I (IGF-I), and testosterone (T) are important mediators of muscle protein synthesis, and thus muscle mass, all of which decline with age. We hypothesized that circulating hormones would be related to the transcriptional levels of their respective receptors and that this expression would be negatively related to expression of the myostatin gene. We therefore determined content of mRNA transcripts (by RT-PCR) for GH receptor (GHR), IGF-I, androgen receptor (AR), and myostatin in skeletal muscle biopsy samples from 27 healthy men >65 yr of age. There were no significant relationships between age, lean body mass, or percent body fat and transcript levels of GHR, IGF-I, AR, or myostatin. Moreover, there were no significant correlations of serum GH, IGF-I, or T with their corresponding target mRNA levels (GHR, intramuscular IGF-I, or AR) in skeletal muscle. However, GHR was negatively correlated ( r = −0.60, P = 0.001) with myostatin mRNA levels. The lack of apparent relationships of muscle transcripts with their respective ligands in healthy older adults suggests that age-related deficits in both GH and T may lead to an increase in myostatin expression and a disassociation in autocrine IGF-I effects on muscle protein synthesis, both of which could contribute to age-related sarcopenia.
Long-term growth hormone excess induces marked alterations in lipoprotein metabolism in mice
Authors: Frick Fredrik , Bohlooly-Y Mohammad , Lindén Daniel , Olsson Bob , Törnell Jan , Edén Staffan , Oscarsson Jan
Published: December 2017

The effects of long-term chronic growth hormone (GH) excess on lipid and lipoprotein metabolism were investigated in 8-mo-old bovine GH (bGH)-transgenic mice. Total body weight, serum cholesterol, insulin-like growth factor-I, and insulin levels were higher, whereas serum levels of glucose, free fatty acids, and triglycerides were lower in transgenic mice. Very low-density lipoprotein (VLDL) cholesterol levels were lower, and low-density lipoprotein (LDL) cholesterol levels were higher, in transgenic mice irrespective of gender, whereas only transgenic male mice had higher high-density lipoprotein cholesterol levels. Total serum apolipoprotein B (apoB) levels were not affected, but the amount of apoB in the LDL fraction was higher in transgenic mice. Hepatic LDL receptor expression was unchanged, whereas apoB mRNA editing and hepatic triglyceride secretion rate were reduced in bGH-transgenic male mice. Both lipoprotein lipase activity in adipose and heart tissue and β-adrenergic-stimulated lipolysis were increased in transgenic male mice. The relative weight of adipose tissue was lower in transgenic mice, whereas hepatic triglyceride content was unchanged. Fat feeding of the mice equalized serum triglycerides and free fatty acids in bGH-transgenic and control mice. In summary, long-term GH excess is associated with marked alterations in lipid and lipoprotein metabolism, indicating decreased production and increased degradation of VLDL and preferential flux of fatty acids to muscle tissues.
Activation of AMP kinase enhances sensitivity of muscle glucose transport to insulin
Authors: Fisher Jonathan S. , Gao Jiaping , Han Dong-Ho , Holloszy John O. , Nolte Lorraine A.
Published: December 2017

Evidence has accumulated that activation of AMP kinase (AMPK) mediates the acute increase in glucose transport induced by exercise. As the exercise-induced, insulin-independent increase in glucose transport wears off, it is followed by an increase in muscle insulin sensitivity. The major purpose of this study was to determine whether hypoxia and 5-aminoimidazole-4-carboxamide-1-β-d-ribofuranoside (AICAR), which also activate AMPK and stimulate glucose transport, also induce an increase in insulin sensitivity. We found that the increase in glucose transport in response to 30 μU/ml insulin was about twofold greater in rat epitrochlearis muscles that had been made hypoxic or treated with AICAR 3.5 h previously than in untreated control muscles. This increase in insulin sensitivity was similar to that induced by a 2-h bout of swimming or 10 min of in vitro electrically stimulated contractions. Neither phosphatidylinositol 3-kinase activity nor protein kinase B (PKB) phosphorylation in response to 30 μU/ml insulin was enhanced by prior exercise or AICAR treatment that increased insulin sensitivity of glucose transport. Inhibition of protein synthesis by inclusion of cycloheximide in the incubation medium for 3.5 h after exercise did not prevent the increase in insulin sensitivity. Contractions, hypoxia, and treatment with AICAR all caused a two- to three-fold increase in AMPK activity over the resting level. These results provide evidence that the increase in insulin sensitivity of muscle glucose transport that follows exercise is mediated by activation of AMPK and involves a step beyond PKB in the pathway by which insulin stimulates glucose transport.
Reduced synthesis of NO causes marked alterations in myocardial substrate metabolism in conscious dogs
Authors: Recchia Fabio A. , Osorio Juan Carlos , Chandler Margaret P. , Xu Xiaobin , Panchal Ashish R. , Lopaschuk Gary D. , Hintze Thomas H. , Stanley William C.
Published: December 2017

To test whether the acute reduction of nitric oxide (NO) synthesis causes changes in cardiac substrate metabolism and in the activity of key enzymes of fatty acid and glucose oxidation, we blocked NOS by giving Nω-nitro-l-arginine methyl ester (l-NAME; 35 mg/kg iv two times) to nine chronically instrumented dogs. [3H]oleate, [14C]glucose, and [13C]lactate were infused to measure the rate of cardiac substrate uptake and oxidation. Glyceraldehyde-3-phosphate dehydrogenase, acetyl-CoA carboxylase, and malonyl-CoA decarboxylase activities were measured in myocardial biopsies. In eight control dogs, ANG II was infused (20–40 ng · kg−1· min−1) to mimic the hemodynamic effects of l-NAME. Afterl-NAME, significant changes occurred for fatty acid oxidation (from 9.8 ± 0.8 to 7.1 ± 1.2 μmol/min), glucose uptake (from 12.9 ± 5.5 to 45.0 ± 14.2 μmol/min), and oxidation (from 4.4 ± 1.2 to 19.9 ± 2.3 μmol/min). ANG caused only a significantly lower increase in glucose oxidation. Lactate uptake increased by more than twofold in both groups. The enzyme activities did not differ significantly between the two groups. In conclusion, the acute inhibition of NO synthesis causes marked metabolic alterations that do not involve key rate-controlling enzymes of fatty acid oxidation nor glyceraldehyde-3-phosphate dehydrogenase.
Influence of endurance running and recovery diet on intramyocellular lipid content in women: a1H NMR study
Authors: Larson-Meyer D. Enette , Newcomer Bradley R. , Hunter Gary R.
Published: December 2017

Using a randomly assigned crossover design, we evaluated the change in intramyocellular lipid stores (IMCL) from baseline after a 2-h treadmill run [67% of maximal oxygen uptake (V˙o2 max)] and the recovery of IMCL in response to a postexercise very low-fat (10% of energy, LFAT) or moderate-fat (35% of energy, MFAT) recovery diet in seven female runners. IMCL was measured in soleus muscle by use of water-suppressed1H-NMR spectroscopic imaging before (baseline), after, and ∼22 h and 70 h after the run. IMCL fell by ∼25% ( P < 0.05) during the endurance run and was dependent on dietary fat content for postexercise recovery ( P = 0.038, diet × time interaction). Consumption of the MFAT recovery diet allowed IMCL stores to return to baseline by 22 h and to overshoot (vs. baseline) by 70 h postexercise. In contrast, consumption of the LFAT recovery diet did not allow IMCL stores to return to baseline even by 70 h after the endurance run ( P < 0.01 at 70 h). These results suggest that a certain quantity of dietary fat is required to replenish IMCL after endurance running.
Inhibition of the creatine kinase reaction decreases the contractile reserve of isolated rat hearts
Authors: Hamman B. L. , Bittl J. A. , Jacobus W. E. , Allen P. D. , Spencer R. S. , Tian R. , Ingwall J. S.
Published: December 2017

To define the relation between phosphoryl transfer via creatine kinase (CK) and the ability of the intact beating heart to do work, we chemically inhibited CK activity and then measured cardiac performance under physiological and acute stress conditions. Isolated perfused rat hearts were exposed to iodoacetamide (IA) and subjected to one of three cardiac stresses: hypercalcemic (Ca2+ = 3 mM) buffer perfusion (n = 7), norepinephrine (2 mumol/min) infusion (n = 6), or hypoxic buffer perfusion (n = 5). IA decreased CK activity to near zero, measured in intact hearts by 31P magnetization transfer, and to 2% of control CK activity, measured in myocardial homogenates. The CK isoenzyme profile was unchanged, suggesting nonselective IA inhibition of all isoenzymes. Mitochondria isolated from IA-treated hearts had normal ADP:O ratios, state 3 respiratory rates, and unchanged acceptor and respiratory control ratios. Neither actomyosin adenosinetriphosphatase nor adenylate kinase activities were changed. After IA exposure, end-diastolic pressure, left ventricular developed pressure, and heart rate were unchanged for at least 30 min at physiological perfusion pressures, but large changes were observed during stress conditions. The increase in left ventricular developed pressure induced by hypercalcemic perfusion and by norepinephrine infusion decreased by 39 and 54%, respectively. During hypoxia, the rate of phosphocreatine depletion was decreased by 57%, left ventricular developed pressure declined, and end-diastolic pressure increased faster than in controls. These results show that inhibition of CK to < 2% of control activity by IA reduced contractile reserve by approximately 50%. We conclude that CK activity is essential for the expression of the full dynamic range of myocardial performance.
Cardiac muscle diseases in genetically engineered mice: evolution of molecular physiology
Authors: Chien K. R.
Published: December 2017

Recent advances in molecular, cellular, and genetically based technologies now offer the possibility of generating genetically engineered mice that display physiological phenotypes with direct relevance to human pathophysiological states. The ability to create gene ablations, gene duplications, and gene modifications should allow the use of genetic approaches to map in vivo pathways responsible for complex physiological phenotypes. Recent work from our laboratory utilizing this approach to study cardiac muscle diseases in both the adult context (cardiac hypertrophy) and in the embryonic context (congenital ventricular defects) will be discussed, as well as the steps that led to the generation and characterization of these novel mouse model systems. A large body of work from independent laboratories now points to the inception of a new field of molecular physiology that will fuse mouse genetics and in vivo physiology using appropriate miniaturized physiological technology. Recent advances and prospects for future directions are summarized.
Effect of L-NMMA, cromakalim, and glibenclamide on cerebral blood flow in hypercapnia and hypoxia
Authors: Reid J. M. , Davies A. G. , Ashcroft F. M. , Paterson D. J.
Published: December 2017

Sulfonylureas reduce cerebral blood flow (CBF) during hypoxia but not during hypercapnia, whereas blockers of nitric oxide (NO) synthesis reduce hypercapnic CBF. However, the effect of NO blockers on hypoxic CBF is uncertain. CBF was measured in the cortex of 51 enflurane-anesthetized rats by the hydrogen clearance technique during eucapnia, hypercapnia (arterial PCO2 65 Torr), and hypoxia (arterial PO2 40 Torr). CBF increased twofold in both hypercapnia and hypoxia from eucapnia. Intracortical (ic) NG-monomethyl-L-arginine (L-NMMA, 100 microM-5 mM) attenuated both the hypercapnic and hypoxic dilations by 60-70%, and L-arginine (300 mg/kg iv) partially reversed these effects. Glibenclamide (10 microM ic) and L-NMMA gave no further attenuation of the hypoxic dilation than L-NMMA alone. Cromakalim (10 microM, ic) increased CBF in eucapnia, but this was not seen in the presence of glibenclamide. The adenosine antagonist 8-phenyl-theophylline did not attenuate the hypoxic dilation. This suggests that NO synthesis plays a major role in the regulation of CBF in hypercapnia and hypoxia. But the combined effects of glibenclamide and L-NMMA do not further attenuate CBF in hypoxia.
Age-related changes in perimicrovascular protein distribution
Authors: Barber B. J. , Dutta S. , Parameswaran S. , Babbitt R. A.
Published: December 2017

The diffusion hypothesis for physiological aging proposes that an increase in interstitial matrix fiber-to-gel ratio causes a decrease in nutrient diffusion to the cells. This hypothesis predicts a decrease in interstitial matrix protein with age. The objective was to test this hypothesis by determining age-related changes in plasma protein distribution in perimicrovascular and distal regions of rat mesentery interstitial matrix. Rats that were 77, 140, 210, 315, 455, and 630 days old were anesthetized with pentobarbital sodium, and a mesenteric loop was exteriorized. Intravital video microspectrophotometry was performed using wavelengths of 280, 320, and 700 nm. Perimicrovascular protein concentrations from the protein absorbance images were used to obtain the histogram, mean, and skewness of the proximal and distal protein concentration distributions. An exponential gradient model was also used to obtain the proximal and distal protein concentrations and gradient decay constants. Proximal protein concentration increased from 77- to 140-day-old rat and then decreased gradually through 210-, 315-, 455-, and 630-day-old rats. Distal concentration decreased gradually from 140- to 630-day-old rats. There was an increase in positive skewness of the proximal protein distributions from 140- through 630-day-old rats. We found an age-related decrease in perimicrovascular protein and propose that this is due to a decrease in protein permeability with age. The results support the diffusion theory of aging.
Direct detection and quantification of singlet oxygen during ischemia and reperfusion in rat hearts
Authors: Zhai X. , Ashraf M.
Published: December 2017

To detect singlet oxygen (1O2) in postischemic reperfused hearts, 5,8-endoperoxide, an oxidation product of beta-carotene, was used as a marker for 1O2 generation and was quantified using high-performance liquid chromatography (HPLC). Isolated rat hearts were subjected to ischemia for 5, 10, 20, 30, and 60 min followed by 10 min of reperfusion with buffer containing 25 microM beta-carotene. The coronary effluent was collected, extracted, and injected into the HPLC unit. The production of 5,8-endoperoxide was maximum during the first 2 min of reperfusion. Maximal accumulated amount of 1O2 was observed in hearts subjected to 60-min ischemia (36.2 +/- 1.7 nmol.10 min-1.g-1) as compared with 10-min ischemia (6.2 +/- 1.0 nmol.10 min-1.g-1). There was a good correlation between the amount of 1O2 production and cardiac function. Treatment with 25 mM histidine significantly decreased 5,8-endoperoxide from 7.02 +/- 0.47 to 0.98 +/- 0.11 nmol.min-1.g-1 (P < 0.01) and improved cardiac function in the group with 60-min ischemia. This study demonstrates that 1) the present method is useful and reliable for the measurement of 1O2 in the heart, 2) 1O2 production during reperfusion is dependent on the duration of initial ischemia, and 3) 1O2 is one of the major factors in postischemic reperfusion injury.
Vasoactive intestinal polypeptide antagonists attenuate vagally induced tachycardia in the anesthetized dog
Authors: Hill M. R. , Wallick D. W. , Mongeon L. R. , Martin P. J. , Levy M. N.
Published: December 2017

We used three vasoactive intestinal polypeptide (VIP) antagonists, VIP-(10-28), [p-Cl-D-Phe6,Leu17]VIP, and NT-VIP, to evaluate the role of VIP as a mediator of vagally induced tachycardia in chloralose-anesthetized dogs. After we administered muscarinic and beta-adrenergic receptor antagonists, we evoked vagally induced tachycardia either directly, by stimulating the vagus nerves for 2 min, or reflexly, by injecting phenylephrine to increase blood pressure. Furthermore, each of the antagonists attenuated the tachycardias induced by vagal stimulation by approximately 50% and the reflexly induced tachycardias by approximately 70%. Each VIP antagonist attenuated the chronotropic responses that we evoked by injecting VIP (5.2 ng/kg) into the sinus node artery. We tested the specificity of these VIP antagonists by determining whether they attenuated the increases in heart rate evoked by two other neuropeptides [peptide histidine isoleucine (PHI) and glucagon]. VIP-(10-28) attenuated the response to PHI, but not to glucagon. The other two VIP antagonists did not alter the chronotropic responses to PHI or glucagon. Our results support the hypothesis that neurally released VIP is the principal mediator of vagally induced tachycardia in the dog.
Endothelial inhibition of myofilament calcium response in intact cardiac myocytes
Authors: Pepper C. B. , Lang D. , Lewis M. J. , Shah A. M.
Published: December 2017

Recent studies suggest that factors released by endothelial cells can modify contraction of isolated cardiac preparations. We compared the effects of 1) coronary effluent collected from Langendorff-perfused rat hearts and 2) cultured vascular endothelial cell superfusate on isolated fura 2-loaded rat ventricular cardiac myocytes. Coronary and cultured cell effluent produced similar effects. Isotonic contraction amplitude was reduced by 31.6 +/- 2.6 and 70.2 +/- 9.1%, respectively; myocyte diastolic length increased by 0.8 +/- 0.2 and 1.5 +/- 0.4 microns, and time to 50% relaxation fell by 6.2 +/- 1.8 and 10.1 +/- 2.0% (all P < 0.05; n = 29 and 15 myocytes, respectively). A small fall in the amplitude of the intracellular Ca2+ transient was observed (8.5 +/- 1.5 and 10.9 +/- 3.5%, respectively; both P < 0.01), insufficient to account for the reduction in twitch amplitude. In intact myocytes tetanized in the presence of thapsigargin, the steady-state myofilament response to Ca2+ was reduced by coronary and cultured cell effluent. These results suggest that both coronary endothelial cells in situ and cultured endothelial cells tonically release a factor(s) that reduces myofilament Ca2+ response.
Catecholamine response to chronic ANG II infusion and its role in myocyte and coronary vascular damage
Authors: Henegar J. R. , Brower G. L. , Kabour A. , Janicki J. S.
Published: December 2017

Acute elevations in circulating angiotensin II (ANG II) are known to increase circulating norepinephrine (NE) levels. However, the time course of catecholamine release relative to chronic ANG II infusion is not known. Furthermore, it is unknown if this ANG II-induced catecholamine release is ANG II type 1 (AT1) receptor mediated or whether the increase in serum catecholamines is responsible for the myocyte and coronary vascular damage seen within the first 3 days of chronic ANG II infusion. Therefore, we examined the influence of chronic ANG II stimulation on serum catecholamine levels with and without AT1 blockade and the effect of beta-blockade on ANG II-induced myocyte and coronary vascular damage. The results indicate that NE release is AT1 mediated, but NE is not significantly elevated until day 4 of ANG II infusion after which it remains elevated. beta-Blockade prevented most ANG II-related myocyte necrosis and coronary vascular damage. Therefore, myocyte and coronary vascular damage do not appear to be related to increased serum NE levels, but instead may be due to the release of neural catecholamines within the heart.
Adenosine A1 receptor-induced upregulation of protein kinase C: role of pertussis toxin-sensitive G protein(s)
Authors: Marala R. B. , Mustafa S. J.
Published: December 2017

Biochemical and pharmacological studies have established that adenosine modulates protein kinase C (PKC), which plays an important role in the maintenance of vascular tone. Our earlier studies [Marala and Mustafa. Am. J. Physiol. 268 (Heart Circ. Physiol. 37): H271-H277, 1995. Marala, R. B., K. Ways, and S. J. Mustafa. Am. J. Physiol. 264 (Heart Circ. Physiol. 33): H1465-H1471, 1993] have shown the involvement of adenosine A1 receptors and not the A2 receptors in the upregulation of PKC in porcine coronary artery. The mechanism(s) by which adenosine upregulates PKC is not yet clearly understood. We now report the increased expression of PKC by adenosine A1 receptor through an upstream activation of pertussis toxin-sensitive G protein(s). Incubation of porcine coronary artery for 24 h with a relatively specific A1-receptor agonist (2S)-N6-(2-endo-norbornyl)adenosine (ENBA) elevated the contractile responses to endothelin-1 by about twofold, probably due to an increased expression of PKC. Incubation of porcine coronary artery with ENBA also protected against the phorbol 12,13-dibutyrate (PDBu)-induced depletion of PKC. Inclusion of pertussis toxin in the incubation medium completely blocked both the upregulatory and the protective effects of ENBA. Incubation with pertussis toxin did not alter the PKC activity as judged by the contractile responses to PDBu. On the contrary, incubation of porcine coronary artery with cholera toxin for 24 h did not alter any of the ENBA responses (upregulation of PKC and the protection against PDBu-induced PKC depletion). Incubation conditions of coronary arteries with toxins are sufficient to cause ADP ribosylation of respective G proteins as judged by back ADP ribosylation studies.(ABSTRACT TRUNCATED AT 250 WORDS)
Modulation of pacemaker activity of sinoatrial node cells by electrical load imposed by an atrial cell model
Authors: Watanabe E. I. , Honjo H. , Anno T. , Boyett M. R. , Kodama I. , Toyama J.
Published: December 2017

To investigate the electrotonic modulation of sinoatrial (SA) node pacemaker activity by atrial muscle, single or multiple (2-7) SA node cells isolated from rabbit hearts were connected to a membrane model [resistance-capacitance (R-C) circuit] of an atrial cell through an external circuit that mimics the gap junctional conductance (Gc) between cells. When Gc was 0 nS (uncoupled conditions), all the preparations generated regular and stable spontaneous action potentials with a mean cycle length (SCL) of 263 +/- 45 ms (+/- SD, n = 35). Step increases of Gc were associated with a progressive prolongation of SCL. At sufficiently high values of Gc, the spontaneous activity became irregular and finally stopped. We defined the threshold Gc causing an appreciable SCL irregularity as the minimum Gc at which the ratio of SD to mean of SCL was > 0.3. The threshold Gc for a single SA node cell was calculated to be 0.58 nS. In the presence of acetylcholine (ACh; 0.05-0.2 microM), the coupling-induced inhibition of spontaneous activity was greatly increased, and the threshold Gc for a single SA node cell was decreased in a concentration-dependent manner. These findings show that the pacemaker activity of SA node cells is easily inhibited when the cells are coupled to a passive atrial cell model and the inhibition is amplified by ACh. Computer simulation using a modified Oxsoft HEART model indicates that the passive atrial cell model acts as a current sink, imposing a substantial outward current on the SA node cell, and ACh amplifies the effect by activating an additional outward current.
Microvascular blood volume-to-flow relationships in porcine heart wall: whole body CT evaluation in vivo
Authors: Liu Y. H. , Bahn R. C. , Ritman E. L.
Published: December 2017

The goal of this study was to evaluate the functional behavior of recruitable (mostly capillary) and nonrecruitable (mostly arterioles and venules) components of the intramyocardial microvasculature in the in situ heart of intact experimental animals. For this purpose fast X-ray computerized tomography (CT) scans were performed in a group of anesthetized pigs. Each scan was performed during an aortic root angiogram and was repeated after sequential injections of a suspension of nonradioactive microspheres into a selected coronary artery. Regional myocardial perfusion (F, ml.g-1.min-1) and intramyocardial blood volume (rho, ml/g) were estimated from the dynamic CT image sequences. For the intramyocardial microcirculation, rho = AF + B square root of F [where A = 0.016 min and B = 0.076 (ml.min/g)1/2] was shown to describe the rho-to-F relationship over the entire range of flows observed. With increasing embolization with 15-microns diameter microspheres, the coefficients A and B changed in a way consistent with A describing the transit time through the functionally recruitable component and B/ square root of F describing the transit time through the functionally nonrecruitable component of the microcirculation.
Differential expression of alpha- and beta-enolase genes during rat heart development and hypertrophy
Authors: Keller A. , Rouzeau J. D. , Farhadian F. , Wisnewsky C. , Marotte F. , Lamande N. , Samuel J. L. , Schwartz K. , Lazar M. , Lucas M.
Published: December 2017

We have analyzed the transition between isoforms of the glycolytic enzyme enolase (2-phospho-D-glycerate hydrolyase; EC 4.2.1.11) in rat heart during normal and pathological growth. A striking fall in embryonic alpha-enolase gene expression occurs during cardiac development, mostly controlled at pretranslational steps. In fetal and neonatal hearts, muscle-specific beta-enolase gene expression is a minor contributor to total enolase. Control mechanisms of beta-enolase gene expression must include posttranscriptional steps. Aortic stenosis induces a rapid and drastic decrease in beta-enolase transcript level in cardiomyocytes, followed by the fall in beta-subunit level. In contrast, alpha-enolase transcript level is not significantly altered, although the corresponding subunit level increases in nonmuscle cells. We conclude that, like fetal heart, hypertrophic heart is characterized by a high ratio of alpha- to beta-enolase subunit concentrations. This study indicates that the decrease in beta-enolase gene expression may be linked to beneficial energetic changes in contractile properties occurring during cardiac hypertrophy
Nonlinear resistances in hepatic microcirculation
Authors: Maass-Moreno R. , Rothe C. F.
Published: December 2017

The liver provides a reservoir available for mobilizing large amounts of blood, but if a change in downstream (outflow) pressure below a certain magnitude (break pressure) does not change upstream pressures, blood volume redistribution may be limited. For downstream pressures larger than the break pressure, the upstream pressures change proportionately. We tested the hypothesis that this nonlinear mode of pressure transmission could be found from the abdominal vena cava to the hepatic microcirculation and from the hepatic microcirculation to the portal vein. Using a servo-null micropipette technique, we measured microvascular pressures at the liver surface of rabbits. In 16 of 30 measurements, increasing the pressure at the liver outflow, by partially occluding the caudal thoracic vena cava, caused an increase in hepatic venular pressure only after the abdominal vena caval pressure exceeded a break pressure of 2.85 +/- 0.92 mmHg. In 13 of 31 measurements, portal venous pressure was not changed until the hepatic venular pressure exceeded a break pressure of 3.36 +/- 0.54 mmHg. Similar behavior and values were obtained for sinusoids and portal venules. When present, the sharp inflection in the upstream-downstream pressure plots suggests that this may be caused by a Starling resistor-type mechanism. When the break was absent, the downstream pressure may have been larger than the break pressure. We conclude that significant hepatic resistances with nonlinear characteristics exist upstream and downstream to the central venules, sinusoids, and portal venules.
Mechanism of mitral leaflet excursion
Authors: Dent J. M. , Spotnitz W. D. , Nolan S. P. , Jayaweera A. R. , Glasheen W. P. , Kaul S.
Published: December 2017

The factors that influence the extent of mitral leaflet opening (MLO) and closure (MLC) have not been defined. We hypothesized that left ventricular (LV) systolic function determines the rate of increase of the early diastolic left atrial (LA)-LV pressure gradient, which is responsible for the extent of MLO, and also the rate of change of the early systolic LV-LA pressure gradient, which determines the degree of MLC. Accordingly, global LV function was changed by altering left main coronary artery flow with LA pressure held relatively constant. LV end-systolic dimension and peak positive LV rate of pressure development (dP/dt) correlated best with the degrees of MLO and MLC, with average correlation coefficients of 0.88 and 0.68, and 0.86 and 0.72, respectively. Although transsecting the submitral apparatus resulted in flailing of the mitral leaflets during normal LV systolic function, the extents of MLO and MLC during LV systolic dysfunction were still influenced by LV systolic function. It is concluded that LV systolic function determines the extent (both opening and closure) of mitral leaflet excursion.
Role of adenosine in regulation of coronary flow in dogs with inhibited synthesis of endothelium-derived nitric oxide
Authors: Matsunaga T. , Okumura K. , Tsunoda R. , Tayama S. , Tabuchi T. , Yasue H.
Published: December 2017

Endothelium-derived nitric oxide (NO) regulates coronary blood flow, but it is unclear how NO synthesis inhibition affects myocardial metabolism. In pentobarbital sodium-anesthetized dogs, myocardial oxygen metabolism, adenosine release, lactate extraction rate (LER), and systolic ventricular wall thickening (SWT) at baseline and during atrial pacing were estimated before and after intracoronary NG-nitro-L-arginine methyl ester (L-NAME) infusion. Coronary blood flow and PO2 in the anterior interventricular vein at baseline were both significantly decreased by L-NAME (3 x 10(-4) M in the coronary blood). Coronary flow was increased during pacing, which was not affected by L-NAME. Myocardial adenosine release remained unchanged during pacing before L-NAME, but it was significantly increased after L-NAME infusion. Neither LER nor SWT changed during pacing performed before and after L-NAME. The experiment was also performed in dogs pretreated with 8-phenyltheophyl-line. After L-NAME, pacing-induced increase in coronary flow was suppressed, and both LER and SWT were significantly decreased during pacing. In conclusion, when NO synthesis is inhibited, adenosine release is increased in response to the increase in myocardial oxygen demand. With this compensatory adenosine release, coronary flow is increased and ventricular function is unaffected.
Response of Ca(2+)-loaded, depolarized guinea pig myocytes to critically timed premature stimulations
Authors: Nordin C.
Published: December 2017

Single premature stimulations during trains of nondriven action potentials induced by depolarization normally cause a transient hyperpolarization of diastolic membrane potential before the subsequent spontaneous upstroke. However, rare, marked transient depolarizations have also been reported. This paper presents experimental data and computer simulations that characterize transient depolarization following premature stimulations and investigate the role of intracellular [Ca2+] in generating this unusual response. In isolated guinea pig myocytes, transient depolarizations (range 4-58 mV) consistently occurred following stimulations 100-160 ms after the upstroke of spontaneous action potentials during exposure to K(+)-free Tyrode solution, which raises intracellular [Ca2+]. In contrast, no transient depolarizations developed when stimulations were delivered during injection of constant inward current or brief exposure to very low dose of Ba2+ (250-500 microM). The experimental response to K(+)-free Tyrode solution was reproduced by a computer model of the transmembrane current and intracellular Ca2+ flux of an isolated guinea pig ventricular myocyte (24) following reduction of extracellular [K+] below 1 mM. Transient depolarization was generated primarily by Na/Ca exchange. Simulations using only those equations governing intracellular Ca2+ cycling revealed that bursts of Ca2+ into the myoplasm after Ca2+ loading caused a transient increase in trough myoplasmic [Ca2+] when the coupling interval following the upstroke of a myoplasmic [Ca2+] oscillation was nearly identical to those coupling intervals that caused pacing-induced transient depolarization of membrane potential after the upstroke of an action potential. These results suggest that transient depolarizations following nondriven action potentials arise from critically timed, stimulus-induced perturbation of intracellular [Ca2+] oscillations associated with Ca2+ overload. Simulations using a multicellular model suggest that critically timed premature stimulations can initiate trains of depolarized, nondriven action potentials in otherwise quiescent, Ca(2+)-overloaded heterogeneous syncytia by a similar mechanism.
Antenatal betamethasone therapy potentiates nitric oxide-mediated relaxation of preterm ovine coronary arteries
Authors: Gao Y. , Zhou H. , Raj J. U.
Published: December 2017

The present study was designed to test the hypothesis that betamethasone may potentiate nitric oxide-mediated relaxation of coronary arteries of preterm lambs. Isolated coronary arteries were obtained from lambs delivered at 128 days gestation. The lambs were treated intramuscularly with a single dose of betamethasone or saline 48 h before delivery and were killed after 3 h of ventilation after delivery. Vessel rings were suspended in organ chambers filled with modified Krebs-Ringer solution (95% O2-5% CO2, 37 degrees C), and their isometric tension was recorded. The endothelium-dependent relaxation induced by bradykinin and calcium ionophore A23187 was greater in arteries from antenatal betamethasone-treated lambs than in arteries from control lambs. The relaxation was abolished by N omega-nitro-L-arginine. Nitric oxide induced a greater relaxation in vessels from antenatal betamethasone-treated lambs and in vessels preincubated with betamethasone than in vessels from controls. Coronary arteries from control and antenatal betamethasone-treated lambs relaxed similarly to 8-bromoguanosine 3',5'-cyclic monophosphate. Nitric oxide induced a greater increase in guanosine 3',5'-cyclic monophosphate content in coronary arteries from antenatal betamethasone-treated lambs than in arteries from control lambs. Our data suggest that antenatal betamethasone therapy potentiates nitric oxide-mediated relaxation in coronary arteries from preterm lambs, probably by affecting the activity of soluble guanylate cyclase of vascular smooth muscle cells.
Midwall LV mechanics in rats with or without renovascular hypertension: effect of different Na+ intakes
Authors: De Simone G. , Devereux R. B. , Volpe M. , Camargo M. J. , Wallerson D. C. , Laragh J. H.
Published: December 2017

Supranormal left ventricular (LV) function has been reported in one-kidney, one-clip (1K,1C) and two-kidney, one-clip (2K,1C) Goldblatt hypertension. However, this finding might be at least partially due to mismatching endocardial rather than midwall fractional shortening to mean end-systolic stress. Accordingly, relations of echocardiographic endocardial and midwall shortening to circumferential end-systolic stress were calculated in 40 Wistar rats on 0.4% NaCl (r = -0.92, SE of estimate = 4.3% and r = -0.62, SE of estimate = 3.2%, both P < 0.0001). Midwall shortening as a percentage of predicted was related to LV chamber diameter in normal animals (r = 0.56, P < 0.0001). Endocardial and midwall shortening were compared as percentage of the normal values predicted from wall stress in 34 2K,1C and 19 1K,1C on 0.4% Na+ 8-9 wk after surgery. Use of midwall shortening reduced the number of these hypertensive rats with supranormal observed-to-predicted shortening ratio from 28 to 7.5% (P < 0.0001). Salt-deprived and high-salt diets (0.0035 and 4% NaCl, respectively) were given to 16 and 18 additional controls, 9 and 7 2K,1C, and 7 and 7 1K,1C. Salt-deprived sham animals had greater endocardial and midwall shortening (106 +/- 7 and 111 +/- 10% of predicted, both P < 0.002) than sham rats on 0.4% NaCl, whereas 4% NaCl had no effect. Five of sixteen salt-deprived sham rats had supranormal observed-to-predicted midwall shortening ratios for LV chamber size, suggesting an enhanced inotropic state. Salt-deprived and high-salt diets had negligible effects on LV performance in Goldblatt rats. Thus use of midwall shortening reduces the number of renovascular hypertensive rats with apparently increased LV function. Salt deprivation stimulates LV myocardial function in normal rats independent of chamber dimension (i.e., an indirect measure of preload) but does not influence LV performance in Goldblatt hypertension 8 wk after renal artery clipping.
Nitrogen dioxide causes pulmonary arterial relaxation via thiol nitrosation and NO formation
Authors: Davidson C. A. , Kaminski P. M. , Wu M. , Wolin M. S.
Published: December 2017

Micromolar concentrations of nitrogen dioxide (NO2), a key metabolite of nitric oxide (NO) and peroxynitrite (ONOO-), were observed to cause a prolonged relaxation of isolated endothelium-removed rings of bovine pulmonary arteries (BPA) precontracted with 30 mM potassium. Relaxation to NO2 was markedly inhibited by 1 microM hemoglobin (Hb), 10 microM methylene blue (MB), and 10 microM LY-83583. The response to NO2 was enhanced in the presence of 1 mM reduced glutathione (GSH) or cysteine. The addition of NO2 to Krebs bicarbonate buffer (under 95% N2-5% CO2) containing 1 mM GSH or BPA resulted in an increase in NO formation (measured in head space gas). Relaxation to NO2 and NO formation were markedly decreased after GSH depletion by pretreatment of BPA with diethyl maleate. A high-performance liquid chromatography analysis of the products formed immediately after the addition of NO2 to GSH detected a previously isolated (but not identified) potent relaxing agent formed by a reaction of GSH with ONOO-, and this material comigrated with a synthetic product thought to be S-nitro-GSH (GSNO2). Nanomolar concentrations of GSNO2 caused a potent dose-dependent relaxation that was inhibited by Hb, MB, and LY-83583. Therefore NO2 appears to cause a prolonged guanosine 3',53'-cyclic monophosphate-mediated relaxation in BPA via thiol nitration and a subsequent time-dependent release of NO. Thus NO2 (and ONOO-) may function in a tissue hormonelike regulatory role in inflammatory processes in which large amounts of these species are produced.
NE-induced contraction, alpha 1-adrenergic receptors, and Ins(1,4,5)P3 responses in cerebral arteries
Authors: Longo L. D. , Ueno N. , Zhao Y. , Zhang L. , Pearce W. J.
Published: December 2017

Adrenergic-mediated responses in cerebral vessels in vitro differ with vessel segment. We performed this study to test the hypothesis that these vessel-specific cerebral artery norepinephrine (NE)-induced contractility changes are mediated in part by differences in alpha 1-adrenergic receptor (alpha 1-R) density (Bmax) or antagonist dissociation constant (KD), and/or inositol 1,4,5-trisphosphate [Ins(1,4,5)P3] synthesis. In common carotid (Com), circle of Willis (Wil), and middle cerebral arteries (MCA) from adult sheep we measured NE-induced contractions. We also quantified alpha 1-R in these, and in anterior, middle, and posterior (AMP) cerebral arteries and cerebral microvessels (Micro). In addition, we quantified NE-induced Ins(1,4,5)P3 synthesis. pD2 values of Com and MCA were 5.2 +/- 0.1 and 6.3 +/- 0.1, respectively. In contrast, the MCA maximum response to NE compared with K+ was much lower than that of the Com. In the Com, Wil, AMP, and Micro, alpha 1-R Bmax was 54 +/- 3, < 5 +/- 2, 23 +/- 3, and 35 +/- 3 fmol/mg protein, respectively. KD averaged 0.20 +/- 0.05 nM in the several vessel groups. In Com and in AMP cerebral arteries, NE produced a rapid increase in Ins(1,4,5)P3 with a peak at 45 s, and 50% effective concentration of 5.5 +/- 0.2 microM. NE stimulated a 240% increase of Ins(1,4,5)P3 in both Com and AMP, whereas Wil showed essentially no response. The ovine MCA was more sensitive to NE than was the Com. In contrast, MCA showed a much lower maximum contractile response to NE compared with K+. Cerebral arteries (AMP) had only about half the alpha 1-R density of the Com. In AMP cerebral arteries, both the basal and NE-stimulated Ins(1,4,5)P3 values were much less than those of the Com. In MCA, the ratio of Ins(1,4,5)P3 response to alpha 1-R Bmax was much greater than in Com. These findings suggest important artery-to-artery differences in components of the cerebrovascular alpha 1-R-mediated contractile pathway. They also suggest considerable potential for modulation of pharmacomechanical coupling and homeostatic regulation of cerebrovascular tone.
Stimulation of atrial natriuretic peptide release by neurokinins in neonatal rat ventricular cardiomyocytes
Authors: Church D. J. , Arkinstall S. J. , Vallotton M. B. , Chollet A. , Kawashima E. , Lang U.
Published: December 2017

The effect of substance P (SP) on atrial natriuretic peptide (ANP) release was studied in neonatal rat ventricular cardiomyocytes. Incubation of cells with SP led to a marked increase in ANP secretion, a response accompanied by increases in alpha-type protein kinase C (PKC) in the membranous cell fraction and 6-keto-prostaglandin F1 alpha (6-keto-PGF1 alpha) formation and a small increase in adenosine 3',5'-cyclic monophosphate (cAMP) production. A role for PKC in SP-induced 6-keto-PGF1 alpha formation and ANP release was apparent insofar as the responses were suppressed by PKC inhibitors and in PKC-downregulated cells. Furthermore, SP-induced 6-keto-PGF1 alpha production was strongly correlated with SP-induced ANP secretion (r = 0.91, P < 0.0001, n = 27), suggesting a role for prostaglandins in SP-mediated ANP release. Supporting this, indomethacin abolished SP-induced ANP release, whereas PGE2, PGF2 alpha, and prostacyclin (PGI2) promoted ANP secretion in this system. Both the profile of SP-induced cAMP production and results obtained with prostaglandin antagonists suggest that a prostanoid FP receptor is at the basis of this response. Finally, both neurokinins A and B induced similar ANP responses, whereas cultured cells were found to contain mRNA transcripts coding for both neurokinin NK1 and NK3 receptor subtypes. Overall, these results suggest that SP induces ANP secretion in neonatal ventricular cardiomyocytes through a PKC- and prostaglandin-dependent signaling pathway.
Singlet oxygen scavengers affect laser-dye impairment of endothelium-dependent responses of brain arterioles
Authors: Rosenblum W. I. , Nelson G. H.
Published: December 2017

This study investigates the possible role of singlet oxygen in accounting for the inhibitory effect of laser-dye injury on endothelium-dependent dilations. The combination of helium-neon (HeNe) laser (20-s exposure) and intravascular Evans blue impairs endothelium-dependent dilation of mouse pial arterioles by acetylcholine (ACh), bradykinin (BK), and calcium ionophore A23187. Each has a different endothelium-derived mediator (EDRFACh, EDRFBK, EDRFionophore, respectively). In this study, diameters at a craniotomy site were monitored in vivo with an image splitter-television microscope. The laser-dye injury, as usual, abolished the responses 10 and 30 min after injury, with recovery, complete or partial, at 60 min. Dilations by sodium nitroprusside, an endothelium-independent dilator, were not affected by laser-dye. When the singlet oxygen scavengers L-histidine (10(-3) M) and L-tryptophan (10(-2) M) were added to the suffusate over the site, the responses to ACh at 10 and 30 min were relatively intact, the response to BK was partly protected at 10 min only, and the response to ionophore was still totally impaired at 10 and 30 min. Lysine, a nonscavenging amino acid, had no protective effects with any dilator. We postulate that a heat-induced injury initiates a chain of events resulting in prolonged singlet oxygen generation by the endothelial cell (not by the dye). We postulate further that destruction of EDRFACh by singlet oxygen is responsible for laser-dye inhibition of ACh and that generation of the radical must continue for > or = 30 min. On the other hand, the heat injury itself is probably responsible for the elimination of the response to ionophore. Heat plus singlet oxygen generated by heat-damaged tissue may initially impair the response to BK, but by 30 min only the effects of some other factor, presumably heat injury, account for the impaired response to BK.