bluuebunny/crossref_metadata_2025 huggingface dataset:
Endotoxin-induced contractile dysfunction in guinea pig hearts is not mediated by nitric oxide
Authors: Decking U. K. , Flesche C. W. , Godecke A. , Schrader J.
Published: December 2017

The decreased contraction amplitude of isolated cardiac myocytes from guinea pigs exposed to lipopolysaccharide (LPS) was reported to be partially reversed by nitro-L-arginine methyl ester (L-NAME), an inhibitor of nitric oxide synthase (NOS) [Brady, et al., Am. J. Physiol. 263 (Heart Circ. Physiol. 32): H1963-H1966, 1992]. We have tested the potential involvement of NO formation in LPS-induced cardiac depression in the intact heart. Isolated perfused hearts of LPS-treated guinea pigs (4 mg/kg 4 h before organ removal) displayed a greatly decreased left ventricular pressure (LVP) when compared with untreated controls (48 +/- 11 vs. 93 +/- 18 mmHg, n = 6 hearts each), whereas heart rate and coronary flow were similar. Perfusion of LPS-treated hearts with L-NMMA or L-NAME (100 microM each) at constant flow did not increase LVP (50 +/- 14 and 44 +/- 11, respectively, vs. 52 +/- 14 mmHg). However, coronary resistance increased significantly. There was no difference between LPS-treated and control hearts in venous adenosine release (104 +/- 58 vs. 133 +/- 86 pmol.min-1.g-1). Measurement of the activities of the induced (iNOS) and constitutive forms of NOS revealed that there was no difference in total NOS activity (237 +/- 82 vs. 181 +/- 97 fmol.min-1.mg protein-1. There was no measurable induction of iNOS in the LPS-treated hearts either. Finally, cardiac energy status was studied by 31P nuclear magnetic resonance spectroscopy. There was no difference between LPS-treated and control hearts in myocardial ATP, creatine phosphate, pH, and free ADP (59 +/- 20 vs. 50 +/- 27 microM).(ABSTRACT TRUNCATED AT 250 WORDS)
Endogenous adenosine modulates alpha 2- but not alpha 1-adrenergic constriction of coronary arterioles
Authors: DeFily D. V. , Patterson J. L. , Chilian W. M.
Published: December 2017

In the coronary circulation alpha-adrenergic constriction competes with metabolic vasodilation. Because adenosine is produced by the working myocardium and metabolic stimulation results in arteriolar dilation, we tested the hypothesis that coronary arteriolar alpha-adrenergic constriction is attenuated by the endogenous production of adenosine. To test this hypothesis, using fluorescence microscopy during stroboscopic epi-illumination of the epicardial microvasculature, we measured the diameter of coronary arterioles in anesthetized open-chest dogs. Measurements were made in the presence of beta-blockade during selective alpha 1- or alpha 2-adrenoceptor activation (phenylephrine or B-HT-933, respectively) before and in the presence of the nonselective adenosine receptor antagonist 8-p-sulfophenyltheophylline (8-pSPT) and expressed as a percent change in microvascular diameter relative to baseline. alpha 1-Activation produced constriction of coronary arterioles under control conditions, which was not augmented after adenosine antagonism (-12 +/- 2 vs. -7 +/- 3%). In contrast, alpha 2-activation did not constrict coronary arterioles under control conditions; however, blockade of adenosine receptors unmasked a significant constriction (0 +/- 2 vs. -7 +/- 2%, P < 0.05). Also adenosine antagonism did not significantly alter the baseline diameter of coronary arterioles. These results demonstrate that endogenously produced adenosine modulates alpha 2-adrenergic constriction of coronary arterioles but not alpha 1-adrenergic constriction, and therefore we speculate that the competition between alpha-adrenergic constriction and metabolic vasodilation is mediated by the alpha 1-adrenoceptor.
Altered contractile and ion channel function in rabbit portal vein with dietary atherosclerosis
Authors: Cox R. H. , Tulenko T. N.
Published: December 2017

This study was performed to determine the effects of dietary atherosclerosis on the pharmacology and ion channel properties of rabbit portal vein (PV). New Zealand White rabbits were fed normal rabbit chow +/- 2% cholesterol for 10 wk. Contractions to norepinephrine (NE) and serotonin were studied under isometric conditions with longitudinal strips. Ca2+ and K+ currents (ICa and IK, respectively) were recorded in freshly dispersed myocytes by whole cell voltage clamp methods. Cholesterol feeding increased total plasma cholesterol levels from 28.4 +/- 5.2 to 1,387 +/- 172 mg/dl as well as the cholesterol-to-phospholipid molar ratio of the PV from 0.34 +/- 0.02 to 0.66 +/- 0.08. Only maximum contractile responses to serotonin were larger in atherosclerotic PV when normalized to the maximum KCl response. Concentration-active stress curves of the atherosclerotic PV to NE and serotonin were shifted to the left. Maximum values of ICa were larger in myocytes from atherosclerotic compared with control animals (4.4 +/- 0.4 vs. 3.1 +/- 0.2 pA/pF, P < 0.05). The voltage dependence of activation and availability of ICa was shifted toward more negative potentials by approximately 10 mV. Whole cell K+ currents were smaller in atherosclerotic myocytes. At a test voltage of +20 mV, IK averaged 14.9 +/- 2.8 pA/pF in control compared with 7.7 +/- 0.8 pA/pF in atherosclerotic myocytes from a holding potential of -80 mV with external Ca2+ concentration of 5 mM. The reversal potential for IK tail currents was significantly less negative in atherosclerotic myocytes (-70 +/- 1 vs. -64 +/- 1 mV).(ABSTRACT TRUNCATED AT 250 WORDS)
Effects of adenosine in simulated ischemia and reperfusion in guinea pig ventricular myocytes
Authors: Cordeiro J. M. , Ferrier G. R. , Howlett S. E.
Published: December 2017

Effects of adenosine (ADN) on cardiac cellular electrical and contractile activity were determined during ischemia and reperfusion. Electrical activity was recorded with conventional and voltage-clamp techniques. Contractions were monitored with a video edge detector. Myocytes were exposed to simulated ischemia (20 min), in the presence or absence of ADN (1-50 microM), and reperfused with Tyrode solution. ADN had no effects under control conditions. However, action potential abbreviation during ischemia was greater in the presence of ADN than for control, and recovery was delayed. In ischemia, Ca2+ current declined equally, and contractions were abolished in control and ADN-treated myocytes. In early reperfusion, oscillatory afterpotentials (OAP), transient inward current (ITI) and aftercontractions appeared, and contractions increased above preischemic levels. ADN abolished contractile overshoot and reduced incidence of OAP, ITI, and aftercontractions from 78 to 37.5%. The effects of exogenous ADN were inhibited by ADN A1-receptor blockade. Inhibition of endogenous ADN by 8-phenyltheophylline only increased incidence of ITI. Thus exogenous ADN in ischemia may protect the myocardium in reperfusion via A1 receptors.
Circadian aspects of apparent correlation dimension in human heart rate dynamics
Authors: Van Leeuwen P. , Bettermann H. , An der Heiden U. , Kummell H. C.
Published: December 2017

The purpose of this study was to examine changes in complexity of cardiac dynamics over 24 h. With use of Holter monitoring, 27 24-h electrocardiogram recordings were obtained from 15 healthy subjects. For each recording, the apparent dimension (DA) was calculated for consecutive sections of 500 heartbeats. These were used to determine nighttime and daytime dimension (D(An) and D(Ad), respectively) as well as the difference between D(An) and D(Ad) (delta DA). Mean 24-h DA, D(An), and D(Ad) were 5.9 +/- 0.3, 6.3 +/- 0.5, and 5.6 +/- 0.6, respectively. D(An) was significantly higher than D(Ad) (P < 0.001), with a mean delta DA of 0.6 +/- 0.7. Furthermore, 67% of delta DA values were significantly different from zero at the 0.05 level. The results show that dimension analysis may be applied to heart rate dynamics to reveal circadian differences of heart rate complexity. We suggest that the decreased complexity during daytime may result from the synchronization of physiological functions. The increase in complexity at night would then correspond to an uncoupling of these functions during the regenerative period.
Nitric oxide and prostaglandins interact to mediate arteriolar dilation during cortical spreading depression
Authors: Meng W. , Colonna D. M. , Tobin J. R. , Busija D. W.
Published: December 2017

We examined whether blockade of prostaglandin synthesis by indomethacin could attenuate the effect of nitric oxide synthase (NOS) inhibition on cerebral arteriolar dilation during cortical spreading depression (CSD). CSD was induced by microinjection of 5% (670 mM) KCl onto the cerebral cortex of anesthetized adult rabbits. A closed cranial window and intravital microscopy were used to measure pial arteriolar diameter, and NOS activity was determined by the conversion assay of [14C]arginine to [14C]citrulline. CSD dilated pial arterioles by 47 +/- 3% (baseline = 80-88 microns) (n = 21, P < 0.05), and inhibition of NOS by NG-nitro-L-arginine (L-NNA) (15 mg/kg iv) reduced dilation during CSD by over one-half (n = 8, P < 0.05) without altering the onset latency to CSD. After indomethacin administration (15 mg/kg iv), CSD dilated arterioles from 73 +/- 2 to 152 +/- 6 microns (n = 4, P < 0.05). However, after administration of both indomethacin and L-NNA (n = 5), CSD-induced arteriolar dilation was not different from the situation where indomethacin alone was given. Thus indomethacin completely abolished the inhibitory effect of L-NNA on CSD-induced dilation. Administration of L-NNA inhibited NOS activity in brain cortex almost completely (n = 8, P < 0.05), whereas indomethacin itself had no effect (n = 8). In addition, L-NNA inhibited topical acetylcholine (10(-5) M)-induced arteriolar dilation (n = 3, P < 0.05), and this effect was not altered by indomethacin (n = 4). In summary, L-NNA reduced arteriolar dilation during CSD. However, after administration of indomethacin, L-NNA does not reduce CSD-induced arteriolar dilation.
Regional epinephrine kinetics in human heart failure: evidence for extra-adrenal, nonneural release
Authors: Kaye D. M. , Lefkovits J. , Cox H. , Lambert G. , Jennings G. , Turner A. , Esler M. D.
Published: December 2017

A number of neurohumoral processes are activated in heart failure, including an increase in the plasma concentration of epinephrine. Radiotracer methods were applied in 42 patients with severe heart failure and 31 healthy volunteers to ascertain the rate at which epinephrine is released to plasma and to evaluate the contribution of extra-adrenal sources. The increase in arterial plasma epinephrine observed in the heart failure patients was explained principally by a 34% (P < 0.001) reduction in the whole body clearance rate of epinephrine from plasma. Regional venous sampling from the heart, lungs, and hepatomesenteric beds was performed in a subgroup of the study population, revealing a significant increase in the release rate of epinephrine to plasma from these organs in heart failure which accounted for 26% of the whole body plasma epinephrine appearance rate. To establish whether the cardiac epinephrine release was of neuronal origin, a physical (cycling) or mental (difficult mental arithmetic) stressor was applied as a sympathoexcitatory stimulus, given that a proportional release of norepinephrine and epinephrine could be expected if sympathetic nerves were the source. These interventions caused significant increases in the regional spillover of norepinephrine to plasma but not that of epinephrine. These findings suggest that nonadrenal tissues contribute significantly to the whole body epinephrine release rate in heart failure and that this may arise from a site other than sympathetic neurons.
GTP requirement for isoproterenol activation of calcium channels in vascular myocytes
Authors: Shi Q. Y. , Cox R. H.
Published: December 2017

The effects of activating the beta-adrenoceptor pathway on calcium current (ICa) in rabbit portal vein (PV) were studied in myocytes freshly isolated by collagenase and elastase treatment. ICa was measured at room temperature (20 degrees C) using whole cell, voltage-clamp methods from a holding potential of -60 mV in cells dialyzed with a pipette solution containing (mM) 100 CsCl, 20 tetraethylammonium chloride, 5 NaCl, 5 MgATP, 20 N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid (HEPES), and 10 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA). The cells were superfused with a solution containing (mM) 140 NaCl, 5 KCl, 1 MgCl2, 5 CaCl2, 10 HEPES, and 10 glucose. Only L-type ICa was present in these myocytes, averaging 3.5 +/- 0.3 pA/pF at +10 mV under control conditions. With 0.1 mM guanosine 5'-triphosphate (GTP) added to the pipette solution, 1 microM isoproterenol (Iso) or forskolin (Fsk) uniformly increased ICa: Iso by 45 +/- 5% and Fsk by 88 +/- 11%. This augmentation of ICa was not associated with significant changes in the voltage dependence of activation or inactivation but was associated with a small increase in the rate of inactivation of ICa. Fsk was also associated with an increased rate of ICa activation. The Iso effect was blocked by pretreatment with 1 microM propranolol and reversed by propranolol after Iso exposure. The ICa response to 10 microM Iso or Fsk was smaller than the response to 1 microM, with some cells showing a steady-state reduction in ICa. When the latter occurred, the voltage dependence of availability was shifted to the left by 5 +/- 0.4 mV.(ABSTRACT TRUNCATED AT 250 WORDS)
Effects of moderate repetitive ischemia on myocardial substrate utilization
Authors: Liedtke A. J. , Renstrom B. , Hacker T. A. , Nellis S. H.
Published: December 2017

The purpose of this report was to directly measure the influence of antecedent ischemia or repetitive ischemia on subsequent rates of intermediary metabolism, specifically exogenous glucose utilization and fatty acid oxidation, with the use of myocardial equilibrium labeling with [U-14C]palmitate and [5-3H]glucose. Twenty-one intact, working, extracorporeally perfused pig hearts were prepared and divided into three groups. These groups included 7 control hearts and 14 comparison hearts, which were exposed to either one cycle (cycle 1, n = 7) or four cycles (cycle 4, n = 7) of brief (5-10 min), moderate (70% decrease in flow below aerobic values) precursory ischemia to the left anterior descending (LAD) circulation followed by aerobic reperfusion. All groups then underwent a 40 min sustained LAD ischemia (60% decrease in flow below aerobic levels) and 40 min aerobic reperfusion. Treatment with one cycle of transient ischemia did not significantly modify the pattern of glycolytic flux from control values during sustained ischemia (over a ninefold increase in average control and cycle 1 values above aerobic levels). However, repetitive ischemia in cycle 4 hearts demonstrably attenuated glycolytic flux during the same interval (-45% from control hearts, P < 0.046). Glucose utilization rapidly returned to near-aerobic values in all three groups during reperfusion but was again appreciably lower (P < 0.004 from control values) in cycle 4 hearts. Fatty acid oxidation averaged 12.3 +/- 1.2 mumol.h-1.g dry wt-1 in all three groups during sustained ischemia and 21.3 +/- 2.0 mumol.h-1.g dry wt-1 during reperfusion (not significant among groups for either perfusion interval).(ABSTRACT TRUNCATED AT 250 WORDS)
Regulation of PDGF-A: a possible mechanism for angiotensin II-induced vascular growth
Authors: Wang D. H. , Prewitt R. L. , Beebe S. J.
Published: December 2017

This study was designed to determine the effects of angiotensin II infusion on structure of conduit and resistance arteries and to see if the effects correlate with changes in platelet-derived growth factor A chain (PDGF-A) gene and protein expression. Wistar rats were subcutaneously infused by osmotic minipump with either angiotensin II (ANG II) at 200 ng.kg-1.min-1 or physiological saline (control) for 14 days. Tail-cuff systolic blood pressure was significantly higher in ANG II compared with control rats beginning the second day of infusion and continuing to the end of 2 wk. Both aorta and external spermatic artery (first-order arteriole of the cremaster muscle) developed increased wall-to-lumen ratios in the ANG II rats, but this occurred by hypertrophy of the wall in the aorta and reduction of the lumen in the arteriole. Digoxigenin-labeled cRNA probes were used for in situ hybridization of vascular sections to identify PDGF-A mRNA. Gene expression of PDGF-A in ANG II rats was upregulated in the hypertrophied aorta and the nonhypertrophied arteriole. With the use of immunocytochemistry techniques, PDGF-A and proliferating cell nuclear antigen were increased in the aorta but not in the arterioles of ANG II rats compared with control rats. These results suggest that the difference in growth response between the aorta and the arteriole induced by ANG II may lie in posttranscriptional modification of PDGF-A mRNA, differential control of transition, or turnover of PDGF-A protein.
Alteration of testicular microvascular pressures during venous pressure elevation
Authors: Sweeney T. E. , Rozum J. S. , Gore R. W.
Published: December 2017

We have addressed the hypothesis that varicocele-related infertility is caused in part by a pressure-induced disturbance of testicular convective transport that upsets the testicular hormonal environment and thus impairs spermatogenesis. The left testis of the hamster [pentobarbital sodium (Nembutal), 70 mg/kg ip] was prepared for microcirculatory observations. Testicular venous pressure was acutely elevated by ligating collateral routes of venous outflow and partially occluding, via a snare, the main venous outflow distal to the pampiniform plexus. Simultaneous direct pressure measurements (servo-null method) were made to monitor venous pressure elevation and quantify resulting pressure and diameter changes in the arterial feed to the testis and in postcapillary venules. The data show that over 90% of the venous pressure elevation (VPE) was transmitted to the postcapillary venules. VPE affected intravascular pressures throughout the testis microvasculature; on average, capsular artery pressure increased by 83% of the VPE, although part of this increase was due to a rise in systemic arterial pressure. Vasoconstriction helped to buffer the pressure rise in the capsular artery, probably at the expense of flow amplitude. Yet the vasoconstriction was ineffective in preventing a rise in exchange vessel pressure. These data suggest that microvascular fluid exchange may be dramatically altered in varicocele, upsetting the hormonal and paracrine environment of the testis, and hence, impairing physiological regulation of gametogenesis.
Alterations in systemic arterial mechanical properties during septic shock: role of fluid resuscitation
Authors: Cholley B. P. , Lang R. M. , Berger D. S. , Korcarz C. , Payen D. , Shroff S. G.
Published: December 2017

The effects of septic shock (endotoxin; EDTX) on arterial mechanical properties were studied in anesthetized rabbits, both in the absence (EDTX alone) and presence (EDTX + fluids) of fluid resuscitation. Aortic pressure-flow (n = 20) and pressure-diameter (n = 10) measurements were used to calculate systemic arterial and regional aortic mechanical properties. At 3 h of EDTX shock, EDTX-alone rabbits had elevated total peripheral resistance (TPR, + 30%, P < 0.05), reduced cardiac output (CO, -40%, P < 0.05), and increased aortic characteristic impedance (Zc, +78%, P < 0.05). In contrast, the EDTX + fluids group responded with decreased TPR (-30%, P < 0.05), a tendency to increase CO (+23%), and elevated Zc (+46%, P < 0.05). A reduction in aortic diameter (-20%, P < 0.05) and an increase in elastic modulus (+50%, P < 0.05) and water content (+23%, P < 0.02) of the aortic wall were observed following endotoxemia. Thus following EDTX 1) “hyperdynamic” septic shock profile (i.e., low TPR, high CO) was observed only when concomitant fluid replacement was provided, 2) aortic wall stiffening was present due to both increased smooth muscle tone and vessel wall edema, and 3) fluid resuscitation resulted in discordant changes in TPR and Zc, suggesting differential flow-induced vasodilation between arteriolar and aortic smooth muscle.
Structural changes and in situ aortic pressure-diameter relationship in long-term chemical-sympathectomized rats
Authors: Lacolley P. , Glaser E. , Challande P. , Boutouyrie P. , Mignot J. P. , Duriez M. , Levy B. , Safar M. , Laurent S.
Published: December 2017

This study determined the effects of long-term chemical sympathectomy with guanethidine (GN) on the mechanical properties and composition of the distal abdominal aorta in Wistar rats. GN was daily administered for 3 mo (3M-GN, from 1 to 12 wk), 5 wk (5W-GN, from 7 to 12 wk), and 8 days (8D-GN, from 11 to 12 wk). All experiments were performed at 12 wk of age to avoid age differences at examination. We used a high-resolution echo-tracking system to determine in situ, in the systolic-diastolic range, the aortic diameter-, compliance-, and distensibility-pressure curves in anesthetized rats. We observed an equivalent significant fall in the tyramine pressor response in all conscious GN-treated rats. Blood pressure was not affected by sympathectomy after 8 days and 5 wk of treatment but was significantly reduced in 3M-GN rats. Chronic sympathetic denervation increased aortic diameter and compliance in 8D-GN rats, compared with those obtained at the same distending pressure in control rats, suggesting vascular smooth muscle relaxation. In contrast, in 5W-GN and 3M-GN rats, the distensibility pressure-curves were significantly shifted toward lower levels of distensibility and pressure, indicating a decreased aortic distensibility at the same level of arterial pressure. Sympathectomy produced a significant reduction in the content of elastin, one of the most distensible components of the arterial wall in 5W-GN and 3M-GN rats. These results suggest that intact sympathetic nerves are necessary to maintain normal functional and structural properties of large arteries in rat. The reduction in aortic distensibility, in long-term sympathectomized rats, could have resulted from complex interactions between local aortic denervation, change in the set point of distending pressure, and changes in aortic smooth muscle tone and/or wall composition.
On the fractal nature of heart rate variability in humans: effects of respiratory sinus arrhythmia
Authors: Yamamoto Y. , Fortrat J. O. , Hughson R. L.
Published: December 2017

The purpose of the present study was to investigate the basic fractal nature of the variability in resting heart rate (HRV), relative to that in breathing frequency (BFV) and tidal volume (TVV), and to test the hypothesis that fractal HRV is due to the fractal BFV and/or TVV in humans. In addition, the possible fractal nature of respiratory volume curves (RVC) and HRV was observed. In the first study, eight subjects were tested while they sat quietly in a comfortable chair for 60 min. Beat-to-beat R-R intervals, i.e., HRV, and breath-by-breath BFV and TVV were measured. In the second study, six subjects were tested while they were in the supine position for 20-30 min. The RVC was monitored continuously together with HRV. Coarse-graining spectral analysis (Yamamoto, Y., and R. L. Hughson, Physica D 68: 250-264, 1993) was applied to these signals to evaluate the percentage of random fractal components in the time series (%Fractal) and the spectral exponent (beta), which characterizes irregularity of the signals. The estimates of beta were determined for each variable only over the range normally used to evaluate HRV. Values for %Fractal and beta of both BFV and TVV were significantly (P < 0.05) greater than those for HRV. In addition, there was no significant (P > 0.05) correlation between the beta values of HRV relative to either BFV (r = 0.14) or TVV (r = 0.34). RVC showed a smooth oscillation as compared with HRV; %Fractal for RVC (42.3 +/- 21.7%, mean +/- SD) was significantly (P < 0.05) lower than that for HRV (78.5 +/- 4.2%).(ABSTRACT TRUNCATED AT 250 WORDS)
Delayed rectifier K+ current in rabbit atrial myocytes
Authors: Muraki K. , Imaizumi Y. , Watanabe M. , Habuchi Y. , Giles W. R.
Published: December 2017

The role of delayed rectifier K+ current(s) (IK) in rabbit left atrium was examined by applying the whole cell voltage-clamp technique to isolated single myocytes. Right-triangular waveforms, which mimic the shape of atrial action potentials (APs), and selective blockers were used to compare the contribution of IK with other K+ currents to repolarization of the APs. IK measured at 34 degrees C in atrial myocytes was very small; the maximum peak amplitude of the tail current (IK,tail) at -40 mV was approximately 50 pA. The IK,tail was almost abolished in most cells (approximately 80%) by the application of 1 microM E-4031, a class III antiarrhythmic drug. The E-4031-sensitive current recorded with the triangular command wave-form showed strong inward rectification and had a maximum amplitude of approximately 30 pA at -40 mV. Total outward current elicited by triangular command pulses depended strongly on stimulation frequency. The main frequency-dependent component was a Ca(2+)-independent transient K+ current (I(t)). I(t) elicited by triangular pulses at 1 Hz was substantially reduced by 4-aminopyridine (4-AP) at potentials positive to 0 mV but was not changed significantly by 1 microM E-4031; 100 microM E-4031 reduced I(t) by approximately 30%. The shape of the APs which were recorded from a single rabbit atrial cell strongly depended on the pulse frequency. Application of 1 microM E-4031 increased action potential duration (APD) in > 50% of cells examined but had little effect on the resting membrane potential (RMP). Application of 0.1 mM BaCl2 also lengthened APD and reduced RMP by approximately 20 mV.(ABSTRACT TRUNCATED AT 250 WORDS)
Isoproterenol infusion induces alterations in expression of hypertrophy-associated genes in rat heart
Authors: Boluyt M. O. , Long X. , Eschenhagen T. , Mende U. , Schmitz W. , Crow M. T. , Lakatta E. G.
Published: December 2017

Chronic infusion of isoproterenol (Iso) in rats results in cardiac hypertrophy via incompletely understood mechanisms. Our purpose was to determine whether Iso infusion would alter the expression of genes associated with hypertrophy. Male Wistar rats received either 2.4 mg Iso.kg-1.day-1, 9.9 mg propranolol (Prop).kg-1.day-1, both Iso and Prop, or vehicle (NaCl) via subcutaneously implanted osmotic pumps. In Iso-treated rats, the ventricular weight-to-body weight ratio was increased by 27% after 1 day and peaked on day 3 (+ 40%). Levels of atrial natriuretic factor (ANF) and fibronectin (FN) mRNA in the left ventricles were elevated 20-fold and 13-fold in Iso-treated rats, respectively, peaking at 3 days of infusion. The increase in FN mRNA accumulation was at least partially accounted for by elevated expression of extra type IIIA and IIIB (EIIIA and EIIIB) splicing variants. Levels of transforming growth factor (TGF)-beta 1 mRNA were elevated twofold after 3 days of Iso infusion. The abundance of skeletal alpha-actin (SK) mRNA increased fourfold after 1 day of Iso and declined thereafter. Iso infusion decreased sarcoplasmic reticulum Ca(2+)-ATPase (SERCA) and preproenkephalin (PNK) gene expression by approximately 50% and induced a myosin heavy chain (MHC) isogene switch favoring beta-MHC. Prop partially inhibited the Iso-evoked increases in ANF and FN mRNA, completely prevented the Iso-induced changes in TGF-beta 1 and SERCA mRNA, but had no effect on the Iso-stimulated changes in SK and PNK gene expression. These results demonstrate that chronic Iso infusion elicits alterations in cardiac gene expression that are consistent with the development of myocyte hypertrophy and interstitial fibrosis and are directionally identical to those previously reported for pressure overload hypertrophy.
Endothelin receptor A blockade alters hemodynamic response to nitric oxide inhibition in rats
Authors: Thompson A. , Valeri C. R. , Lieberthal W.
Published: December 2017

We examined the extent to which the systemic and renal vasoconstriction induced by nitric oxide (NO) inhibition in vivo is mediated by endothelin (ET). We examined the effects of BQ-610, a specific ETA-receptor antagonist, after NO inhibition with N omega-nitro-L-arginine methyl ester (L-NAME) in the anesthetized rat. Mean arterial pressure (MAP) increased after L-NAME infusion from 107 +/- 2 to 133 +/- 3 mmHg (P < 0.05 vs. baseline period) then fell to 115 +/- 3 mmHg after administration of BQ-610 (P < 0.05 vs. L-NAME and baseline periods). Systemic vascular resistance (SVR) increased from 1.26 +/- 0.06 to 2.17 +/- 0.18 mmHg.ml-1.min.300 g after L-NAME (P < 0.05 vs. baseline period) then fell to 1.69 +/- 0.12 mmHg.ml-1.min.300 g after BQ-610 (P < 0.05 vs. L-NAME and baseline periods). The increase in renal vascular resistance (RVR) from 6.4 +/- 0.4 to 13.7 +/- 1.4 mmHg.ml-1.min.300 g induced by L-NAME (P < 0.05 vs. baseline period) was reduced to 11.1 +/- 1.0 mmHg.ml-1.min.300 g by BQ-610 (P < 0.05 vs. L-NAME and baseline periods). The extent to which BQ-610 reversed the L-NAME-induced increases in RVR and SVR was comparable (RVR by 40 +/- 9%; SVR by 52 +/- 7%). Glomerular filtration rate and renal blood flow were both reduced by L-NAME, but neither value increased after BQ-610, possibly because the renal vasodilation induced by ETA blockade was offset by the concomitant reduction in MAP and renal perfusion pressure.(ABSTRACT TRUNCATED AT 250 WORDS)
Capillary diameter changes during low perfusion pressure and reactive hyperemia in rabbit skeletal muscle
Authors: Bosman J. , Tangelder G. J. , Oude Egbrink M. G. , Reneman R. S. , Slaaf D. W.
Published: December 2017

Capillary diameter changes were studied in the tenuissimus muscle of 29 urethan-anesthetized New Zealand White rabbits. Capillaries were visualized with transillumination bright-field microscopy (saltwater lens, x 50; resolution approximately 0.3 microns). Median capillary diameter during the control period was 4.4 microns (range 3.2-6.9 microns). Complete aortic occlusion resulted in a reduction of median femoral arterial pressure to 17 mmHg (range 4-22 mmHg). During 2 min of occlusion, capillary diameter decreased by 6%, with greater change on the arteriolar side of the capillary than on the venular side. During reactive hyperemia after release of the occluder, capillary diameter maximally increased by 12% compared with the control period, with a larger response at the arteriolar end of the capillary than at the venular end. Median capillary resistance was estimated to increase by 27% during occlusion and to decrease by 36% during peak reactive hyperemia. The observed diameter changes are compatible with the idea that capillaries change their diameter relative to changes in transmural pressure.
A human calcium-activated potassium channel gene expressed in vascular smooth muscle
Authors: McCobb D. P. , Fowler N. L. , Featherstone T. , Lingle C. J. , Saito M. , Krause J. E. , Salkoff L.
Published: December 2017

Large-conductance Ca(2+)-activated K+ (BK) channels are widespread and functionally heterogeneous. In other classes of K+ channels, functional heterogeneity derives from large gene families, alternative splicing, heterologous subunit composition, and functional modulation. The molecular basis of mammalian BK channel heterogeneity is unknown, since only a single gene (mSlo) has been identified. BK channels in native vascular smooth muscle have an apparent Ca2+ sensitivity approximately 10-fold greater than native brain or skeletal muscle channels, or cloned mSlo channels. Using mSlo as a low-stringency probe, we screened human arterial smooth muscle and genomic libraries extensively in search of genes or splice variants with novel properties. We isolated the human homologue of mSlo, including two novel splice variant forms, but found no other related genes. Electrophysiological characterization of the hSlo clones in Xenopus oocytes and Chinese hamster ovary cells gave BK currents that were not measurably different from mSlo currents. However, coexpression of hSlo with a recently cloned beta-subunit derived from smooth muscle dramatically increased apparent Ca2+ sensitivity. Thus alpha-subunits alone may not determine Ca2+ sensitivity of vascular smooth muscle BK channels. hSlo was mapped to human chromosome 10q23.1, and the genomic structure was analyzed. Immediately after the amino terminal, two unusual regions of trinucleotide repeating sequences are present. The first of these regions encodes polyglycine, and the second encodes polyserine. Both regions of repeated sequence are conserved between the mouse and human genome.
Measurement of right ventricular volume by conductance catheter in closed-chest pigs
Authors: Stamato T. M. , Szwarc R. S. , Benson L. N.
Published: December 2017

This study details the effects of changes in right ventricular (RV) volume on the conductance catheter gain factor both over a broad volume range and within the cardiac cycle. In seven closed-chest anesthetized pigs, a conductance catheter was introduced transvenously and positioned to span the RV long axis, including the outflow tract. Parallel conductance was determined using a saline dilution technique. Conductance volume gain factor (alpha) was computed using stroke volume obtained by thermodilution over a range of volumes obtained by volume loading or sustained partial occlusion of the inferior caval vein. The chest was then opened, an ultrasonic flow probe was placed around the pulmonary artery, and the conductance-derived RV volume was compared with the pulmonary flow integral over the course of ejection. When volume was varied over a broad range, an inverse relation between RV volume and alpha was observed (P < 0.001). This did not cause significant nonlinearity of the conductance-volume relation. The relation was also relatively linear during the course of ejection within the cardiac cycle. These results indicate that the conductance catheter may be employed, using the described technique, to assess RV volume under steady-state conditions.
Cardiac myocytes release leukocyte-stimulating factors
Authors: Massey K. D. , Strieter R. M. , Kunkel S. L. , Danforth J. M. , Standiford T. J.
Published: December 2017

The production of cytokines directly from cardiac myocytes has not been previously demonstrated and could represent an important mechanism and site of intervention in ischemia and reperfusion injuries. Macrophage inflammatory protein-2 (MIP-2) and monocyte chemotactic protein (MCP) are chemotactic cytokines (chemokines) that stimulate polymorphonuclear leukocytes (PMNs) and monocytes, respectively. Endothelium has been implicated as being a major cellular source of leukocyte-activating factors. We hypothesized that the myocardial cells may also play an important role in producing chemokines independently of endothelium. Primary cultures of adult rat ventricular myocytes were prepared. Cultured myocytes were stimulated with either interleukin 1 (IL-1), tumor necrosis factor (TNF), or lipopolysaccharide (LPS). MIP-2 and MCP mRNA were expressed in adult rat myocytes following stimulation. Our studies indicate that ventricular myocytes expressed chemokine mRNA and protein in both a dose- and time-dependent fashion. MIP-2 and MCP release, determined by enzyme-linked immunosorbent assay, was biologically active, accounting for approximately 40% of the PMN and monocyte chemotactic activity produced by these cells. These results suggest that cardiac myocytes may directly recruit activated leukocytes into areas of injury. Such a recruiting process could underlie the migration of leukocytes into areas of oxidant stress and play a role in development of reperfusion injury of myocardium.
Role of bradykinin in cardiac functional protection after global ischemia-reperfusion in rat heart
Authors: Brew E. C. , Mitchell M. B. , Rehring T. F. , Gamboni-Robertson F. , McIntyre R. C. , Harken A. H. , Banerjee A.
Published: December 2017

We have reported that cardiac preconditioning against ischemia-reperfusion (IR) can be induced by transient ischemia (TI) and alpha 1-adrenoreceptor stimulation, both mediated by protein kinase C (PKC) (Mitchell, M., X. Meng, C. Parker, E. Brew, A. Harken, and A. Banerjee. Circ. Res. 76: 73-81, 1995). Our study objective was to explore the mechanism of endogenous preconditioning and address the role of PKC activation in bradykinin-mediated cardiac functional protection. Isolated rat heart was used to assess the effects of exogenous bradykinin, TI, selective B2-receptor blocker, and PKC antagonism on cardiac functional recovery after a global IR injury. Final recovery of developed pressure was improved in hearts treated with bradykinin and TI compared with controls. Bradykinin- and TI-mediated preconditioning was eliminated with coinfusion of the B2-receptor antagonist. Further evaluation of bradykinin-mediated preconditioning revealed that PKC blockade also eliminated functional protection. Immunofluorescent stains of bradykinin-treated hearts demonstrated translocation and activation of specific PKC isoforms in the preconditioned heart. We conclude that TI-mediated preconditioning involves intrinsic cardiac bradykinin receptor stimulation. Bradykinin, through the B2 receptor, initiates a series of intracellular events culminating in the activation of PKC.
Muscle metaboreceptors in hemodynamic, autonomic, and ventilatory responses to exercise in men
Authors: Piepoli M. , Clark A. L. , Coats A. J.
Published: December 2017

A muscle metaboreceptor (ergoreceptor) contribution to the hemodynamic and autonomic responses to exercise is well recognized, but a ventilatory component remains controversial. Control handgrips were compared with handgrips followed by 4-min regional circulatory occlusion of the exercising muscles to isolate the metaboreceptor role in blood pressure, autonomic tone (spectral analysis of R-R and blood pressure variability), and ventilatory responses to exercise in 11 normal subjects. Exercise responses were maintained after the effort by metaboreflex activation in systolic pressure (136.2 +/- 3.5 vs. 123.0 +/- 4.3 mmHg, P < 0.05), ventilation (19.0 +/- 2.6 vs. 8.5 +/- 0.4 l/min, P < 0.0005), and sympathetic discharge to the heart and circulation (elevated low-frequency components of R-R interval, 1,747.5 +/- 309.2 vs. 1,085.9 +/- 259.1 ms2, P < 0.05, and systolic pressure variability, 45.3 +/- 3.9 vs. 26.5 +/- 4.4 mmHg2, P < 0.005). We conclude that metaboreflex contributes to the sympathetic, hypertensive, and hyperpneic responses to exercise in normal subjects.
Gap junction function in vascular smooth muscle: influence of serotonin
Authors: Moore L. K. , Burt J. M.
Published: December 2017

In this study we examined the effects of serotonin (5-hydroxytryptamine, 5-HT) on the function of gap junctions between smooth muscle cells isolated from human and pig coronary and rat mesentery arteries and between A7r5 cells (cell line derived from embryonic rat aorta). Mesentery and pig coronary cells expressed connexin (Cx) 43, and human coronary cells expressed Cx40. Mesentery and pig coronary cells each exhibited a single gap junction channel population with unitary conductances of 75 and 59 pS, respectively. Human coronary cells exhibited two channel populations with unitary conductances of 51 and 107 pS. The A7r5 cells express Cx40 and Cx43 and exhibit three channel populations with unitary conductances of 70, 108, and 141 pS. Under control conditions, junctional conductance between the four cell types ranged from 11 to 20 nS. During maximal stimulation with 5-HT (1-10 microM), junctional conductance increased (29-75%) in all four cell types. The unitary conductance profiles in the rat mesentery and pig coronary cells were unaffected by 5-HT, suggesting that the observed increase in macroscopic conductance reflects an increase in open probability. Unitary conductances were also unaffected in the human coronary and A7r5 cells. However, there was a reduced frequency of the 105-pS channel in the human coronary cells and of the 70- and 141-pS channels in the A7r5 cells. These changes in the relative frequency histograms suggest that the open probabilities of the various channel types are differentially affected by the 5-HT treatment.(ABSTRACT TRUNCATED AT 250 WORDS)
Regulation of SERCA 2 expression by thyroid hormone in cultured chick embryo cardiomyocytes
Authors: Fisher D. J. , Phillips S. , McQuinn T.
Published: December 2017

We investigated the role of thyroid hormone in the physiological perinatal increase in cardiac sarcoplasmic reticulum (SR) Ca(2+)-adenosinetriphosphatase (ATPase) expression. We isolated and cultured the cardiomyocytes in 10(-8) M triiodothyronine (T3) for 48 h and then measured SR Ca(2+)-ATPase mRNA and immunodetectable protein contents as well as SR-dependent 45Ca2+ uptake rate. We also examined the effect of T3 on expression of the same gene in monkey kidney CV-1 cells, which do not express thyroid hormone receptors. T3 increased cardiomyocyte SR Ca2+ pump mRNA content by 289 +/- 35%, and immunodetectable SR Ca2+ pump protein content by 255 +/- 44%, and SR-specific 45Ca2+ uptake rate by 189 +/- 22% (P < 0.01 for each). In contrast, T3 had no significant effect on the total cellular RNA or protein contents in the cardiomyocyte, and there was no effect of T3 on Ca(2+)-ATPase mRNA content in the thyroid hormone receptor-negative CV-1 cells. These data demonstrate that T3 increases expression of the cardiac SR Ca2+ pump, that the effect can be localized to the cardiomyocyte, and that the effect is dependent on thyroid hormone receptors. These data are consistent with pretranslational and possibly transcriptional level effect of thyroid hormone on the cardiac SR Ca2+ pump gene (SERCA 2). The gestation-associated increase in thyroid hormone may be at least partially responsible for the previously demonstrated perinatal increase in cardiac SR Ca2+ pump expression.
Interrelation between ventricular function, myocardial blood flow, and O2 consumption changes at birth in lambs
Authors: Smolich J. J. , Berger P. J. , Walker A. M.
Published: December 2017

We studied the interrelation of changes in ventricular external work, myocardial blood flow, and O2 consumption at birth. Eleven fetal sheep were instrumented under general anesthesia at 133-134 days gestation with arterial, peripheral venous, and left atrial catheters, and in five fetuses, a catheter was also inserted into the coronary sinus. Fetal left ventricular (LV) and right ventricular (RV) outputs and myocardial blood flows (radioactive microspheres), hemodynamics, and LV O2 consumption were measured 1 wk later. Fetuses were delivered by cesarean section, and measurements were repeated 1 and 4 h after birth. RV minute work (mmHg.l.kg-1) was greater in fetuses (10.8 +/- 0.5 vs. 15.6 +/- 1.0 P < 0.001), but because of increased LV minute work (to 20.9 +/- 1.4, P < 0.005) and unchanged RV minute work, this pattern was reversed by 1 h after birth. RV myocardial blood flow (ml.min-1.100 g-1) was predominant in fetuses (234 +/- 25 vs. 306 +/- 27, P < 0.001), but this also reversed in lambs; this reversal was related to unchanged 1-h (248 +/- 16) and lower 4-h LV myocardial blood flow (199 +/- 9, P < 0.05) and a progressive fall in RV myocardial blood flow (1 h: 245 +/- 20, P < 0.05; 4 h: 174 +/- 12, P < 0.005). LV O2 consumption (ml.min-1.100 g-1) increased between fetal (8.1 +/- 0.6) and 1-h lambs (18.9 +/- 1.3, P < 0.005) because of a rise in the LV arteriovenous O2 content difference (3.6 +/- 0.4 vs. 7.5 +/- 0.6 ml/dl, P < 0.005). External work performed per unit myocardial blood flow (mmHg.l.ml-1) in the LV increased between fetal and 1-h lambs (1.92 +/- 0.14 to 3.33 +/- 0.15, P < 0.001) and, in the RV, between fetal and 4-h lambs (2.09 +/- 0.18 to 2.92 +/- 0.24, P < 0.01). The proportion of consumed O2 converted to external work was, however, similar in fetal (34.6 +/- 3.1%) and 1-h (31.3 +/- 2.9%) and 4-h lambs (34.5 +/- 3.6%). These findings indicate that 1) a switch from a fetal RV to a newborn LV dominance is due to increased LV pumping performance, 2) an associated switch in LV and RV myocardial blood flow patterns is mainly related to a fall in RV myocardial blood flow, 3) a postnatal rise in LV O2 consumption results from enhanced LV arteriovenous O2 extraction, not increased LV myocardial blood flow, 4) ventricular external work per unit myocardial blood flow increases postnatally, particularly in the LV, and 5) LV mechanical efficiency is not altered after birth.
A device for the application of cyclic twist and extension on perfused vascular segments
Authors: Vorp D. A. , Severyn D. A. , Steed D. L. , Webster M. W.
Published: December 2017

Cyclic strain is known to influence many aspects of vascular cell biology, including macromolecular biosynthesis, cell proliferation, and cell morphology. The simulation of the cyclic strain associated with the vasculature in situ has been carried out mostly using devices that manipulated flat membranes on which the cells of choice are cultured. The purpose of this work was to create an apparatus wherein cyclic strains consistent with those found in native blood vessels could be applied to intact three-dimensional (tubular) specimens perfused ex vivo. The cyclic strain protocols using our apparatus may be any combination of axial stretch and twist. Concurrently, the perfusion flow and shear stress are controlled as desired. Vessel diameter, intraluminal pressure, volume flow, and regional strain are measured and stored on line. To illustrate the application of the device, we present hemodynamic and kinematic data collected from a human saphenous vein segment perfused under steady-flow conditions while subjected to cyclic stretch and twist.
Vasorelaxation by an endothelium-derived metabolite of arachidonic acid
Authors: Pfister S. L. , Spitzbarth N. , Edgemond W. , Campbell W. B.
Published: December 2017

Arachidonic acid elicited relaxation responses in normal rabbit aorta precontracted with norepinephrine. The relaxation response was enhanced by the cyclooxygenase inhibitor indomethacin and inhibited by lipoxygenase inhibitors, including nordihydroguaiaretic acid and cinnamyl-3,4-dihydroxy-alpha-cyanocinnamate. The cytochrome P-450 epoxygenase inhibitor metyrapone had no effect on arachidonic acid-induced relaxations. The present study hypothesized that a lipoxygenase metabolite of arachidonic acid mediated the response. Incubation of rabbit aorta with [14C]arachidonic acid resulted in the synthesis of a previously unidentified 14C-labeled metabolite and was called the unknown factor. Production of the unknown factor was not inhibited by indomethacin and decreased by lipoxygenase inhibitors. Production of the unknown factor and arachidonic acid-induced relaxations were dependent on an intact endothelium, indicating that the cellular source of the unknown relaxant factor was the endothelial cell. This was confirmed by demonstrating the ability of cultured rabbit aortic endothelial cells to produce the unknown factor from [14C]arachidonic acid. Feeding rabbits a 2% cholesterol diet for 2 wk induced hypercholesterolemia without causing atherosclerosis. In the cholesterol-fed rabbits, indomethacin enhanced arachidonic acid-induced relaxations in norepinephrine-precontracted aortas (maximal relaxation 49.0 +/- 2.5 vs. 35.5 +/- 1.7%, cholesterol-fed vs. normal) and increased production of the unknown factor compared with normal rabbits. The partially purified unknown factor elicited an approximately 26% inhibition of the vasoconstrictor response to norepinephrine in intact rabbit aorta. Further purification of the unknown factor by reverse-phase high-pressure liquid chromatography system resulted in isolation of a radioactive product that relaxed precontracted rabbit aorta. Therefore these data suggest that in normal and hypercholesterolemic rabbit aorta the endothelium produces an unknown metabolite of arachidonic acid that causes vasorelaxation and may regulate vascular tone.