bluuebunny/crossref_metadata_2025 huggingface dataset:
Regulation of atrial muscarinic K+ channel activity by a cytosolic protein via G protein-independent pathway
Authors: Hong S. G. , Pleumsamran A. , Kim D.
Published: December 2017

Rapid desensitization of the muscarinic K+ current (KACh current) is observed in cell-attached patches with 10 microM acetylcholine in the pipette. When inside-out patches were formed within approximately 1 s after formation of cell-attached patches and GTP was applied to the cytoplasmic side of the membrane, desensitization was not observed, indicating that a cytosolic factor mediated the desensitization. Applying the atrial cytosolic extract directly to the cytoplasmic side of such inside-out patches elicited a rapid desensitization of the KACh current. ATP (1-4 mM) reversed this effect of the cytosol and reverted the KACh channel to the undesensitized state. These effects of ATP and cytosol on the KACh channel could occur in the absence of GTP or in the presence of 100 microM guanosine 5'-O-(3-thiotriphosphate), indicating that G protein was not involved. Treatment of the cytosol with proteases (trypsin, chymotrypsin, bacterial protease) or heat denaturation abolished the effect of the cytosol on the KACh channel kinetics, indicating that the cytosolic factor was a protein. Functional assay of the fractions collected from gel filtration column indicated that the molecular mass of the native protein was 95-130 kDa. We conclude that a large cytosolic protein mediates the rapid desensitization of the KACh channel current via a G protein-independent pathway.
Decreases in steady-state muscle performance and vessel density in reduced renal mass hypertensive rats
Authors: O'Drobinak D. M. , Greene A. S.
Published: December 2017

In this study we hypothesized that reduced renal mass (RRM) hypertension, which is associated with a chronic reduction in vessel density, could reduce steady-state muscle performance. Vessel density and isometric tetanic force from the in situ gastrocnemius-plantaris-soleus muscle group were studied in age-matched normotensive sham-operated control (HSS) and hypertensive RRM rats on a high-salt (4.0% NaCl) diet (HSRRM) and a low-salt (0.4% NaCl) diet (LSS and LSRRM, respectively). The Achilles tendon was isolated and connected to a force transducer. Peak isometric tension elicited by sciatic nerve stimulation (1/s for 10 min, 50 impulses/s for 330 ms) was not different between the groups. In the LSS, HSS, and LSRRM groups, tension decreased similarly at 3 min to 375 +/- 22, 447 +/- 26, and 424 +/- 21 g/g, respectively. Tension was significantly reduced in the HSRRM group (203 +/- 45 g/g) relative to the LSS, HSS, and LSRRM groups by 3 min. These differences in steady-state tension persisted throughout the remainder of the experiment. Microvessel density, measured by the lectin fluorescence technique, was reduced significantly only in the soleus, plantaris, and medial gastrocnemius of the HSRRM rats. We conclude that RRM hypertension results in reductions in vessel density (rarefaction) that are associated with decreased steady-state muscle performance.
Effect of l-NAME on pressure-flow relationships in isolated rabbit lungs: role of red blood cells
Authors: Sprague Randy S. , Stephenson Alan H. , Dimmit Reed A. , Weintraub Neal A. , Branch Carrie A. , McMurdo Lorraine , Lonigro Andrew J.
Published: December 2017

Pages H1941–H1948: Randy S. Sprague, Alan H. Stephenson, Reed A. Dimmit, Neal A. Weintraub, Carrie A. Branch, Lorraine McMurdo, and Andrew J. Lonigro. “Effect of l-NAME on pressure-flow relationships in isolated rabbit lungs: role of red blood cells.” Page H1941: the author name of Neal A. Weintraub should read as Neal L. Weintraub.
Transfer function analysis of central arc of aortic baroreceptor reflex in rabbits
Authors: Kubo T. , Imaizumi T. , Harasawa Y. , Ando S. , Tagawa T. , Endo T. , Shiramoto M. , Takeshita A.
Published: December 2017

While electrically stimulating the aortic depressor nerve (ADN) pseudorandomly, we recorded renal sympathetic nerve activity (RSNA) and systemic arterial pressure (SAP) in 19 alpha-chloralose-anesthetized rabbits with sinoaortic denervation. From the recorded signals, we determined the transfer functions from ADN stimulation by a pseudorandom binary sequence to RSNA [HCMD.RSNA(f)] and to SAP [HCMD.SAP(f)]. The modulus of HCMD.RSNA(f) was flat over 0.0122-0.8 Hz, whereas the phase lag increased linearly with frequency. Thus the central transduction appeared not to modify the relative amplitude of the signals from the baroreflex afferents but to provide a fixed time delay (approximately 400 ms). In contrast, the modulus of HCMD.SAP(f) decreased precipitously toward high frequencies, and the degree of the phase lag was larger than that of HCMD.RSNA(f). We conclude that 1) the transfer property of the central are does not significantly modify the relative amplitude of the frequency components of the baroreflex afferents but provides a fixed time delay and 2) the frequency independence of the modulus of the transfer property is not preserved when the analysis is extended to SAP.
Endogenous myocardial norepinephrine is not essential for ischemic preconditioning in rabbit heart
Authors: Ardell J. L. , Yang X. M. , Barron B. A. , Downey J. M. , Cohen M. V.
Published: December 2017

To determine whether endogenous cardiac catecholamines mediate ischemic preconditioning (PC) in the rabbit heart, myocardial catecholamines were depleted by reserpine (5 mg/kg, 18-24 h pre-PC) or surgical sympathectomy (2 wk pre-PC). In vivo hearts were subjected to 30 min of regional ischemia and 3 h of reperfusion. PC involved either one or four cycles of 5-min ischemia and 10-min reperfusion before the 30-min ischemic period. Right ventricular norepinephrine content (pmol/mg protein), 51.4 +/- 11.1 in untreated rabbits, was reduced to 0.6 +/- 0.2 and 1.8 +/- 0.5 by surgical sympathectomy and reserpine, respectively. Infarct size (IS) was measured by tetrazolium and expressed as percentage of the risk zone. In untreated animals exposed solely to 30 min of regional ischemia IS was 35.5 +/- 1.6% and was unchanged by reserpine (43.3 +/- 5.4%) or surgical sympathectomy (33.4 +/- 3.5%). compared with infarction in the respective non-PC controls, IS in untreated (7.4 +/- 1.5%, P < 0.0001) and surgically sympathectomized (11.2 +/- 1.5%, P < 0.0001) animals was significantly diminished by a single cycle of PC, but the latter exerted less protection in reserpinized animals (27.6 +/- 3.5%, P < 0.0025). Four cycles of PC, however, reduced IS to 10.3 +/- 1.2% in reserpinized animals. Therefore, despite comparable depression of myocardial norepinephrine content, surgical and chemical sympathectomy had different effects on the level of protection afforded by ischemic PC. These data demonstrate that endogenous myocardial catecholamines are not essential for protection from PC in the rabbit.
Agonist- and CPA-induced elevation of cytoplasmic free Ca2+ in intact valvular endothelium from rabbits
Authors: Li L. , van Breemen C.
Published: December 2017

Intracellular Ca2+ signals of intact endothelium from rabbit aortic or pulmonic valves loaded with fura 2 were studied using imaging fluorescence microscopy. Agonists such as ATP or carbachol and inhibitors of endoplasmic reticulum (ER) Ca(2+)-ATPase such as cyclopiazonic acid (CPA), thapsigargin, and 2', 5'-di(tert-butyl)-1, 4,-benzohydroquinone (BHQ) induced an increase in cytoplasmic free Ca2+ concentration ([Ca2+]i) that was maintained above the prestimulated levels as long as extracellular Ca2+ was present, indicating that the maintained [Ca2+]i increase is dependent on the entry of extracellular Ca2+. The voltage-gated channel was not found to contribute to [Ca2+]i increase. SK&F–96365, a receptor-operated cation channel (ROC) blocker, and 2-nitro-4-carboxyphenyl-N, N-diphenylcarbamate (NCDC), a postulated phospholipase C inhibitor, were shown to effectively block ROC, since they greatly reduced the maintained [Ca2+]i increase caused by ATP, but not that caused by CPA, which was blocked by Ni2+. To further investigate the Ca2+ influx involved in this process, divalent cation entry was measured as Mn2+ quenching of fura 2 fluorescence at 360-nm excitation wavelength. At rest, fluorescence quenching at 360 nm by Mn2+ was observed, which was inhibited by Ni2+ but not by NCDC, indicating Mn2+ entry through the leak pathway. The quenching was enhanced following ATP stimulation, and this enhancement was abolished by pretreatment with NCDC. In contrast, the rate of Mn2+ quenching was unaffected by the application of CPA. These results demonstrate that ATP stimulates divalent cation influx that is not related to the Ca2+ content of ER. Abolition of Ca2+ uptake into ER was postulated to increase the effectiveness of the Ca2+ leak in raising [Ca2+]i.
Cytoplasmic phosphates in Na(+)-K+ balance in KCN-poisoned rat heart: a 87Rb-, 23Na-, and 31P-NMR study
Authors: Kupriyanov V. V. , Yang L. , Deslauriers R.
Published: December 2017

The effect on intracellular Na+ ([Na+]i) and Rb+ fluxes if reduced [ATP]/ [ADP] and increased Pi has been investigated by 1 mM potassium cyanide (KCN) or KCl (control) infusion (24 min) in Langendorff perfused rat hearts. 87Rb, 23Na, or 31P nuclear magnetic resonance (NMR) spectra were acquired to measure intracellular Rb+ (a congener for K+, 20% substitution), Na+, and phosphates. KCN infusion (14-24 min) caused decreases in phosphocreatine (34 +/- 12% of initial), ATP (64 +/- 17), and Rb content (71 +/- 7) and increases in Pi (273 +/- 65) and [Na+]i (210 +/- 52). Dimethylamiloride (10 microM) did not change the rate of Na+ accumulation. The rate constant of unidirectional Rb+ efflux (min-1) increased during KCN treatment by 70% (0.061 +/- 0.006 vs. 0.036 +/- 0.004, P = 0.0001). KCN-stimulated Rb+ efflux was inhibited by glibenclamide (Glib, 10 microM. 0.042 +/- 0.009, P = 0.0001 vs. KCN) and alpha-cyano-4-hydroxycinnamate (0.5 mM, 0.047 +/- 0.008, P < 0.002 vs. KCN). KCN moderately decreased the Rb+ influx rate (to 82 +/- 17%, P = 0.01), which was depressed more significantly in the presence of Glib (47 +/- 17%, P = 0.03). We suggest that inhibition of Na(+)-K(+)-adenosinetriphosphatase (ATPase) by Pi is responsible for intracellular Na+ accumulation, whereas K+ loss is associated with both activation of ATP-sensitive K+ channels and the K(+)-lactate-cotransporter and inhibition of Na(+)-K(+)-ATPase.
Inhibition of cytochrome P-450 attenuates hypoxemia of acute lung injury in dogs
Authors: Stephenson A. H. , Sprague R. S. , Weintraub N. L. , McMurdo L. , Lonigro A. J.
Published: December 2017

The intravenous administration of ethchlorvynol (ECV), in dogs, resulted in an acute lung injury (ALI) characterized by a 200 +/- 80% increase in venous admixture and a 142 +/- 30% increase in extravascular lung water (EVLW). Pretreatment with the cytochrome P-450 inhibitor 8-methoxypsoralen prevented the ECV-induced increase in venous admixture but not the increased EVLW. These findings parallel those reported for cyclooxygenase inhibition in ECV-induced ALI and suggest that an arachidonic acid (AA) metabolite of pulmonary cytochrome P-450 activity may mediate the increase in venous admixture of ALI. We demonstrate that canine pulmonary microsomes metabolize [1-(14)C]AA to a variety of products, including the cytochrome P-450 metabolites 5,6-, 8,9-, 11,12-, and 14,15-epoxyeicosatrienoic acid (EET). In prostaglandin F2 alpha-contracted, isolated pulmonary venous rings, 5,6-EET induced relaxation in a concentration-dependent manner. This action of 5,6-EET was prevented by indomethacin (10(-5) M). These results suggest that may serve as the cyclooxygenase-dependent endogenous pulmonary vasodilator responsible for the increase in venous admixture of ECV-induced ALI.
Constancy and variability of contractile efficiency as a function of calcium and cross-bridge kinetics: simulation
Authors: Yamaguchi H. , Takaki M. , Matsubara H. , Yasuhara S. , Suga H.
Published: December 2017

We simulated myocardial Ca2+ (Ca) and cross-bridge (CB) kinetics to get insight into the experimentally observed constancy and variability of cardiac contractile efficiency in generating total mechanical energy under various inotropic and pathological conditions. The simulation consisted of a Ca transient, Ca association and dissociation rate constants of troponin C, and CB on and off rate constants. We evaluated sarcomere isometric twitch contractions at a constant muscle length. We assumed that each CB cycle hydrolyzes one ATP and that the force-length area (FLA) quantifies the total mechanical energy generated by CB cycles in a twitch contraction. FLA is a linear version of pressure-volume area, which quantifies the total mechanical energy of cardiac twitch contraction and correlates linearly with cardiac oxygen consumption (H. Suga, Physiol. Rev. 70: 247-277, 1990). The simulation shows that the contractile efficiency varies with changes in the Ca transient and Ca and CB kinetics except when they simultaneously speed up or slow down proportionally. These results point to possible mechanisms underlying the constancy and variability of cardiac contractile efficiency.
Plasma activation of neutrophil CD18 after skeletal muscle ischemia: a potential mechanism for late systemic injury
Authors: Petrasek P. F. , Lindsay T. F. , Romaschin A. D. , Walker P. M.
Published: December 2017

Reperfusion of acutely ischemic skeletal muscle is associated with neutrophil activation, which may augment local injury or cause damage to distant organs. Polymorphonuclear neutrophil glycoprotein CD18 plays a role in this injury, since its blockade substantially reduces damage; however, its mechanisms of control during reperfusion are poorly understood. The purpose of this study was to investigate the importance of circulating plasma factors to CD18-dependent neutrophil function during reperfusion and to relate these to quantitative expression of CD18. Eight rabbits were subjected to hindlimb ischemia for 5 h, followed by 48 h of reperfusion. Plasma collected at seven intervals was incubated with unstimulated neutrophils from uninjured rabbits. CD18-specific neutrophil activation was evaluated by quantifying adherence to protein-coated polystyrene and by measuring oxidant production, detected by chemiluminescence after exposure to complement-opsonized zymosan. CD18 was quantified cytofluorometrically. Plasma collected at end ischemia and during early reperfusion affected no significant alterations of adhesion, oxidant production, or CD18. Late reperfusion plasma (between 8 and 48 h) significantly increased adherence and oxidant production (to 4.11 +/- 0.61 and 2.60 +/- 0.32 times the values of preischemic plasma, P < 0.006). Peak adherence, oxidant production, and CD18 expression were evoked synchronously by 24 h plasma. CD18 expression increased only at 24 h and did not increase proportional to increases in adherence and oxidant production. Control plasma (nonischemic, n = 5) elicited no significant differences of any inflammatory measure during sham ischemia or reperfusion. These results indicate that endogenous mediators may evoke a progressive systemic inflammatory response after ischemia by stimulating CD18-dependent neutrophil function in a delayed but prolonged manner.
Significance of NO in hemorrhage-induced hemodynamic alterations, organ injury, and mortality in rats
Authors: Yao Y. M. , Bahrami S. , Leichtfried G. , Redl H. , Schlag G.
Published: December 2017

In an attempt to evaluate the role of nitric oxide (NO) in pathophysiological alterations and multiple organ damage caused by hemorrhagic shock, we employed NG-monomethyl-L-arginine (L-NMMA), an inhibitor of NO synthase, in anesthetized rats subjected to a prolonged hypovolemic insult (30-35 mmHg for 180 min). Infusion of 2.0 mg/kg L-NMMA at the end of resuscitation diminished the fall in mean arterial pressure (MAP) and significantly increased the cardiac index and stroke volume, together with remarkable protection from multiple organ damage compared with the controls. The 48-h survival rate was significantly improved from 26.7% in the control group to 68.8% in the treatment group (P < 0.05). In contrast, the high dose of 20.0 mg/kg L-NMMA resulted in a strong blood pressure response, but a marked reduction in cardiac index and stroke volume concomitant with an increased total peripheral resistance index within the observation period, and tended to increase damage to various organs at 2 h after treatment. In addition, marked elevation in both endotoxin and tumor necrosis factor levels were observed in animals subjected to shock insult. The results suggest that NO induced by hemorrhagic shock in rats is an important mediator for pathophysiological alterations associated with cardiovascular abnormalities, multiple organ dysfunction, and even lethality. Regulation of NO generation and use of NO inhibitors might provide new aspects in the treatment of hemorrhage-related disorders, whereas the administration of L-NMMA would be either deleterious or salutary in a dose-dependent manner.
Hemodynamic changes in early pregnancy in chronically instrumented, conscious rats
Authors: Slangen B. F. , Out I. C. , Verkeste C. M. , Peeters L. L.
Published: December 2017

To explore the onset of and the interrelationship between maternal hemodynamic changes in pregnancy, serial hemodynamic measurements were performed in chronically instrumented, conscious rats using electromagnetic flow probes around the ascending aorta and arterial catheters. The rats were studied daily from day 4 to day 12 and on days 14, 18, and 20 of pregnancy. Nonpregnant (NP) rats matched for age and days postsurgery served as controls. In the pregnant (P) group, the hematocrit started to decrease by postconceptional day 6 (day of implantation) to reach a value of 9 +/- 3% below the initial level by day 8. In these 2 days, cardiac output (CO) increased by 9 +/- 4%, as a result of a rise in stroke volume (SV). No changes in mean arterial pressure were observed. In both groups, heart rate (HR) had decreased by day 7. Aortic flow acceleration and peak aortic flow, indicators of myocardial contractility, increased from day 10 on only in the P group. In this context, it should be emphasized that the results of this study do not allow differentiation between the contractile properties of the cardiac muscle and the contractile changes as a result of the altered preload and afterload. By days 12 and 18, CO had increased by 20 +/- 5 and 29 +/- 9%, respectively, above the initial value and by 25 and 40%, respectively, above the value observed in the NP group. The rise in CO after day 14 was accomplished by a concomitant increase in HR and SV and was accompanied by a further increase in myocardial performance. We conclude that hemodynamic changes can already be identified by day 8 of rat pregnancy, 2 days after implantation. The rise in CO in early pregnancy results from a selective increase in SV and is accompanied by a rise in myocardial performance.
Electrophysiological-anatomic correlates of ATP-triggered vagal reflex in the dog. III. Role of cardiac afferents
Authors: Katchanov G. , Xu J. , Hurt C. M. , Pelleg A.
Published: December 2017

To test the hypothesis that the asymmetry in the afferent traffic of the intra-right atrium (RA) ATP-triggered vagal reflex is due to the stimulation by ATP of extrapulmonary (i.e., cardiac) vagal chemosensitive afferent terminals, ATP, adenosine, and capsaicin were given into the canine RA and the aortic root (AR; n = 12); ATP and adenosine were also administered into the left common carotid artery and the descending aorta (n = 6). The negative chronotropic action [i.e., suppression of sinus node (SN) automaticity] of the test compounds and time to peak effect (tp) were determined. Under baseline conditions, ATP given into the left common carotid artery had a relatively very small effect. ATP given into the descending aorta had no effect. In contrast, intra-RA and intra-AR ATP markedly suppressed SN automaticity, the former less than the latter; the opposite was true for capsaicin. Intra-RA adenosine was much less potent than intra-RA ATP. The tp of intra-RA ATP and intra-RA adenosine were larger than the tp of intra-AR ATP. Pulmonary denervation did not alter the effects of intra-RAATP, intra-ARATP, or intra-AR capsaicin but almost abolished the effect of intra-RA capsaicin. Subsequent bilateral, but not left, cervical vagotomy markedly reduce the effects of ATP and eliminated the difference between the effects of ATP and adenosine. In addition, tp of intra-RA ATP and intra-AR ATP increased substantially and were similar to tp of adenosine. It was concluded that 1) ATP can stimulate vagal afferent terminals not only in the lungs but also in the heart, 2) the latter constitutes the vagal component of the negative chronotropic action of intra-RA or intra-AR ATP on SN automatically, and 3) the asymmetry in the vagal afferent traffic elicited by ATP in the heart (i.e., right vagal dominance) supersedes the symmetrical vagal afferent traffic triggered by intrapulmonary ATP.
Age and autonomic effects on interrelationships between lung volume and heart rate
Authors: Stanley G. , Verotta D. , Craft N. , Siegel R. A. , Schwartz J. B.
Published: December 2017

To determine effects of aging and autonomic input on interrelationships between respiratory and heart rate variability, we collected 5 min of lung volume of R-R interval data from 7 young [27 +/- 3(SD) yr] and 10 older (69 +/- 6 yr) healthy supine humans before and after double pharmacological autonomic blockade with propranolol (0.2 mg/kg iv) and atropine (0.04 mg/kg iv). Estimates of respiratory and heart rate power spectra and linear transfer functions between the two groups were generated by Fourier analysis. Age, double blockade effects, the age-drug interactions were determined by analysis of variance for repeated measures. Basal R-R intervals were unaffected by age. Double blockade decreased R-R intervals and variability in both age groups (P < 0.0001), but R-R intervals decreased less in older than in young subjects (P < 0.0001). In contrast, basal respiratory intervals and standard deviation were greater in older subjects (P = 0.05) and were unaffected by double blockade in young and older subjects. Lung volume-to-heart rate spectral coherence was highest at frequencies associated with respiration and greater in young than in older subjects (P < 0.07). Double blockade decreased lung volume-to-heart rate variability transfer function magnitude (P < 0.007) and increased phase angle (P < 0.02) without age effects or age-drug interactions. In conclusion, heart rate, respiration, and respiration-heart rate interrelations are altered by aging, and double autonomic pharmacological blockade does not eliminate all age-related differences.
Endothelial injury in vivo: a technical and statistical approach to the study of aortic integrity
Authors: Skantze H. B. , Bondjers G. , Olofsson B. , Pettersson K. , Svensson A.
Published: December 2017

The endothelium can be a link connecting risk factors with the development of cardiovascular disease, and methods for studying endothelial integrity are therefore important. We describe a method of studying endothelial injury in vivo by combining immunohistochemistry with an improved technique of producing “enface” preparations (Hautchens) aortic endothelium of rabbits and guinea pigs. These Hautchens enabled the study of large numbers of endothelial cells and adherent cells (probably leukocytes) at different locations along the aorta. The statistical distributions of the number of injured endothelial cells and adherent cells in a visual field were also investigated, and both closely followed a log-normal distribution. Based on this distribution, a method to estimate endothelial injury by grouping the cell count data, instead of exact counting, was developed. The grouped cell count data were then used to calculate the grouped mean and grouped standard deviation for each animal. The improvements of the technical and statistical methods offer good opportunities to study various aspects of endothelial integrity in a time efficient manner.
Effects of calponin on force generation by single smooth muscle cells
Authors: Horowitz A. , Clement-Chomienne O. , Walsh M. P. , Tao T. , Katsuyama H. , Morgan K. G.
Published: December 2017

Although the actin-binding and actomyosin adenosinetriphosphatase (ATPase) inhibitory properties of calponin are well documented in vitro, its function in the smooth muscle cell has not been elucidated. To address this question, we utilized the ferret aortic smooth muscle cell, which shows a protein kinase C-dependent contraction even at pCa (-log [Ca2+]) 9.0 in the absence of a change in myosin light chain phosphorylation. Force was recorded from single, briefly permeabilized cells stimulated via a Ca(2+)-independent pathway by either phenylephrine or the epsilon isoenzyme of protein kinase C. Treatment of stimulated cells with wild-type recombinant calponin reduced steady-state contractile force by 45-60%. When calponin application preceded protein kinase C epsilon treatment, contraction was completely suppressed. On the other hand, calponin phosphorylated at Ser175 or mutant calponin with a Ser175 ⇢ Ala replacement had no effect on contractile force. A peptide corresponding to Leu166-Gly194 of calponin, which included an actin-binding domain but excluded the actomyosin ATPase inhibitory region, was synthesized. Treatment of aortic smooth muscle cells with this peptide triggered a concentration-dependent contraction, presumably by alleviating the inhibitory effect of endogenous calponin. A control peptide with a scrambled sequence of the same residues produced no detectable contractile response. Although other interpretations are possible, these results are consistent with the view that calponin participates in thin filament-mediated regulation of smooth muscle contraction and that it may be part of a Ca(2+)-independent pathway downstream of protein kinase C epsilon.
Pulmonary interstitial pressure and proteoglycans during development of pulmonary edema
Authors: Negrini D. , Passi A. , de Luca G. , Miserocchi G.
Published: December 2017

In anesthetized adult rabbits, pulmonary perivascular interstitial pressure (P(ip)), measured by micropuncture technique with intact pleural space, averaged -10.5 +/- 1.9 (SD) cmH2O in control conditions, with a wet-to-dry lung weight ratio (W/D) of 4.8 +/- 0.2. Saline infusion (120 ml i.v. over 120 min) induced interstitial edema, increasing P(ip) to 3.62 +/- 1.6 cmH2O with no significant increase in W/D (5.13 +/- 0.1). For intravenous saline infusion exceeding 140 ml, P(ip) decreased to about atmospheric pressure with development of severe edema that was characterized by an increase of W/D ( > 7) with no further change in P(ip). In a separate set of animals, pulmonary interstitial proteoglycans (PGs) were investigated after sequential extraction of the tissue with 0.4 and 4 M guanidinium chloride (GuHCl) under control conditions and with interstitial (100 ml saline load in 100 min) and severe edema ( > 200 ml total infusion). The extractability of PGs increased constantly with increasing W/D. PG content in total extracts was evaluated by determination of hexuronate content which was 195.4 +/- 1.5 micrograms/g dry tissue in control lungs, 217.9 +/- 1.6 in interstitial edema, and 316.4 +/- 2.7 in severe edema. Moreover, edema development was coupled with an increase in efficiency of PG extraction with 0.4 M GuHCl. These findings suggested a weakening of PG interactions with other components of the extracellular matrix (ECM). Electrophoretic and gel-filtration analyses showed that the relative content of PG populations of large molecular size decreased constantly in 0.4 M GuHCl extract with increasing water loading. We propose relating the inflection of P(ip) in the transition from interstitial to severe edema to PG breakdown, which might greatly affect ECM structural organization, including collagen spreading and/or rupture of epithelial layer.
Determinants of stroke volume and systolic and diastolic aortic pressure
Authors: Stergiopulos N. , Meister J. J. , Westerhof N.
Published: December 2017

We investigated how parameters describing the heart and the arterial system contribute to the systolic and diastolic pressures (Ps and Pd, respectively) and stroke volume (SV). We have described the heart by the varying-elastance model with six parameters and the systemic arterial tree by the three-element windkessel model, leading to a total of nine parameters. Application of dimensional analysis led to a total of six dimensionless parameters describing dimensionless Ps and Pd, i.e., pressures with respect to venous pressure (Ps/Pv and Pd/Pv). SV was normalized with respect to unloaded ventricular volume (Vd). Sensitivity analysis showed that Ps/Pv, Pd/Pv, and SV/Vd could be accurately described by four, three, and three dimensionless parameters, respectively. With this limited number of parameters, it was then possible to obtain empirical analytical expressions for Ps/Pv, Pd/Pv, and SV/Vd. The analytic predictions were tested against the model values and found to be as follows: Ps predicted = (1.0007 +/- 0.0062) Ps, r = 0.987; Pd predicted = (1.016 +/- 0.0085) Pd, r = 0.992; and SV predicted = (0.9987 +/- 0.0028) SV, r = 0.996. We conclude that aortic Ps, Pd, and SV can be accurately described by a limited number of parameters and that, for any condition of the heart and the arterial system, Ps, Pd, and SV can be presented in analytical form.
Formation of an F2-isoprostane in vascular smooth muscle cells by elevated glucose and growth factors
Authors: Natarajan R. , Lanting L. , Gonzales N. , Nadler J.
Published: December 2017

Recently a series of non-cyclooxygenase-derived prostanoids were identified in vivo in humans and in animal models of free radical injury as products of free radical-catalyzed peroxidation of arachidonic acid. One of these, an F2-isoprostane, 8-epiprostaglandin F2 alpha (8-epi-PGF 2 alpha), is a potent renal vasoconstrictor and can increase vascular smooth muscle cell (VSMC) DNA synthesis. In the present study we have evaluated whether F2-isoprostanes play a role in diabetic vascular dysfunction by studying the formation of 8-epi-PGF2 alpha in porcine VSMC (PVSMC) cultured under hyperglycemic conditions. 8-Epi-PGF2 alpha levels were quantitated by a specific enzyme immunoassay. We also examined whether certain VSMC growth factors, such as angiotensin II, platelet-derived growth factor, and transforming growth factor-beta, could also regulate the formation of 8-epi-PGF2 alpha. We observed that PVSMC cultured under high glucose (HG) conditions produced significantly higher amounts of 8-epi-PGF2 alpha compared with normal glucose (NG) conditions (3.7 +/- 0.13 ng/10(6) cells in HG vs. 2.9 +/- 0.2 ng/10(6) cells in NG, P < 0.05). Furthermore, all three growth factors tested evoked significant dose-dependent formation of 8-epi-PGF2 alpha (ranging from 125 to 220% of control). These results suggest that 8-epi-PGF2 alpha formation, as a result of hyperglycemia or due to growth factor action, may lead to increased VSMC growth and contribute to the complications of diabetes and cardiovascular disease.
Pulmonary vascular response to angiotensin II in canine pacing-induced heart failure
Authors: Roy B. J. , Pitts V. H. , Townsley M. I.
Published: December 2017

The effects of angiotensin II(ANG II) on pulmonary vascular resistance and microvascular permeability were studied in isolated, blood-perfused, ventilated canine lung lobes from control animals (n = 40) and animals with pacing-induced heart failure (n = 15). Conditioned dogs were paced (245 beats/min) for 30.6 +/- 0.9 (SE) days until left ventricular shortening fraction decreased by 56% (P < 0.05). Baseline pulmonary arterial resistance (Ra) (19.1 +/- 1.6 vs. 8.0 +/- 1.1 cmH2O.1(-1).min.100g) and venous resistance (Rv) (17.1 +/- 2.3 vs. 7.8 +/- 1.0 cmH2O.1(-1).min.100 g) were greater (P < 0.05) in the paced group compared with controls, respectively. Increments in Ra (delta Ra) and Rv(delta Rv) were measured after intra-arterial boluses of ANG II (1-10 micrograms). ANG II produced a dose-dependent response in delta Ra that was enhanced after pacing (P < 0.05). There was no effect on delta Rv in either group. At increased venous pressure (Pv = 20 cmH2O), the increments in delta Ra were significantly attenuated in both groups. In control lobes at low Pv, delta Ra and delta Rv both tended to decrease with increased lobar blood flow, suggesting that blood flow affects the pulmonary vascular response of ANG II. The baseline capillary filtration coefficient (Kf,c) was not different in the paced group compared with control, nor was there any effect of ANG II on Kf,c in the paced group. However, Kf,c did increase after ANG II in the control groups evaluated at either low or high Pv (P < 0.05). This difference in Kf,c was not seen if the experiment was done at increased Pv but without ANG II administration. We conclude that the pulmonary vasoconstrictor activity of ANG II is modestly enhanced in canine pacing-induced heart failure. Nonetheless, ANG II does not likely contribute to increased pulmonary vascular resistance in vivo in heart failure, since this effect was abolished at increased Pv. Finally, the absence of any effect of ANG II on pulmonary microvascular permeability in the paced group is suggestive of some adaptive remodeling of the capillary endothelial barrier.
Hypoxia does not directly stimulate ischemically sensitive abdominal visceral afferents during ischemia
Authors: Fu L. W. , Pan H. L. , Pitsillides K. F. , Longhurst J. C.
Published: December 2017

Abdominal ischemia activates ischemically sensitive sympathetic visceral afferents and evokes reflex excitation of the cardiovascular system. These afferents respond to ischemic metabolites, including lactic acid, bradykinin, prostaglandins, and reactive oxygen species. Severe hypoxemia also has been shown to activate these afferents. It is not known, however, if the regional tissue hypoxia induced by abdominal ischemia directly or indirectly activates ischemically sensitive visceral afferents. To determine the role of tissue hypoxia in activation of ischemically sensitive abdominal afferents, continuous single-unit activity of ischemically sensitive abdominal sympathetic C-fiber afferents (conduction velocity = 0.51-1.48 m/s) and regional tissue PO2, measured by a polarographic oxygen electrode in the porta hepatis, duodenum, or pancreas, were recorded simultaneously in anesthetized cats before and during 10-15 min of ischemia. Abdominal ischemia rapidly decreased regional tissue PO2 from 161 +/- 10 to 8 +/- 2 mmHg (P < 0.01) within an interval of 136 +/- 12 s. By contrast, after longer latency (399 +/- 24 s, P < 0.01 vs. PO2 interval), the activity of these afferents increased from 0.06 +/- 0.01 to 0.33 +/- 0.07 imp/s (P < 0.01). Furthermore, the activity of ischemically sensitive afferents gradually increased throughout ischemia with peak activity (0.68 +/- 0.14 imp/s) occurring at 600 +/- 39 s, although tissue PO2 remained constant. There was no correlation between the changes of tissue PO2 and discharge activity of these afferents (r = -0.428, P = 0.144). These data suggest that tissue hypoxia induced by abdominal ischemia is not directly responsible for activation of ischemically sensitive sympathetic visceral afferents but likely acts in an indirect fashion by promoting formation of other metabolic products capable of activating these nerve endings.
Infusions of pressor agents selectively attenuate depressor responses to ACh in anesthetized dogs
Authors: Nakahara T. , Ishii K. , Tanaka Y. , Nakayama K.
Published: December 2017

In dogs anesthetized with pentobarbital sodium (30 mg/kg iv), infusions of phenylephrine (PE; 1-3 micrograms.kg-1.min-1 iv for 30 min and longer) caused sustained elevations in blood pressure and suppressed depressor responses to acetylcholine (ACh; 1 microgram/kg iv) in a dose- and time-dependent manner. The dose-response curve for ACh (0.01-100 micrograms/kg iv)-induced depressor responses was shifted to the right by approximately 80-fold after an intravenous infusion of PE (3 micrograms.kg-1.min-1) for 120 min. Similar suppression was observed when infusions of methoxamine (5 micrograms.kg-1.min-1 iv), norepinephrine (3 micrograms.kg-1.min-1 iv under blockade of beta-adrenoceptors), or angiotensin II (0.3 micrograms.kg-1.min-1 iv) were carried out. However, in dogs treated with prazosin (1 mg/kg iv) or hydralazine (1 mg/kg iv) to prevent elevations in blood pressure over the baseline level, PE (3 micrograms.kg-1.min-1 iv) failed to attenuate depressor responses to ACh. The suppression observed after PE infusion was specific to ACh-induced depressor responses; i.e., no suppression was observed on the depressor responses to other drugs, such as histamine, sodium nitroprusside, carbachol, and methacholine. Furthermore, neostigmine (bolus injection of 30 microgram/kg iv followed by an infusion of 15 micrograms.kg-1.h-1 iv) greatly diminished the suppressive effect of PE. Except for a slight increase in acetylcholinesterase (AChE) activity in renal arterial segments, activities of both AChE and butyryl-cholinesterase in plasma, erythrocytes, and pulmonary and renal arterial segments were unchanged after PE infusion. These results suggest that prolonged elevation in blood pressure and/or vasoconstriction selectively attenuates depressor responses to ACh through accelerated degradation of this material.
Determination of PO2 and its heterogeneity in single capillaries
Authors: Zheng L. , Golub A. S. , Pittman R. N.
Published: December 2017

We have applied the phosphorescence lifetime technique (Vanderkooi, J. M., G. Maniara, T. J. Green, and D. F. Wilson. J. Biol. Chem. 262: 5476-5482, 1987) to determine oxygen tension in single capillaries of the hamster retractor muscle. Palladium meso-tetra(4-carboxyphenyl)porphine (10 mg/ml, pH 7.40, bound to bovine serum albumin) was used as the phosphorescent oxygen sensor. Our measurement system consisted of a microscope configured for epi-illumination, a strobe flash lamp, a 430-nm bandpass excitation filter, and a 630-nm cut-on emission filter. A rectangular diaphragm was used to limit the illumination field to 10 microns x 10 microns, and an end-window photomultiplier tube was used to detect the phosphorescence signal, which was then input to an analog-to-digital board in a personal computer. In vitro calibrations were carried out at 37 degrees C on samples flowing through a glass capillary tube (diameter, 300 microns) at four different O2 concentrations (0, 2.5, 5, and 7.5%). In vivo tests were carried out on arterioles, capillaries, and venules of the retractor muscle of anesthetized hamsters. The phosphorescent compound was administered by injection into a jugular vein (20 mg/kg). Phosphorescence decay curves were analyzed by a new model of heterogeneous oxygen distribution in the excitation/emission volume. Mean Po2 values and the local Po2 gradients within the excitation/ emission volume were calculated from phosphorescence life-times obtained from individual decay curves. The time course of Po2 obtained during 0.5-s measurement periods (5 decay curves at 0.1-s intervals) at a given site along a capillary indicated the presence of a gradient in Po2 within the plasma space between and near red blood cells. Similar Po2 gradients were also detected in arterioles and venules. Mean Po2 values for arterioles, capillaries, and venules over the 0.5-s observation period were 27 +/- 5, 14 +/- 2, and 11 +/- 3 (SD) mmHg, respectively. The magnitude of the Po2 gradient in the arterioles, capillaries, and venules was 6 +/- 1, 4 +/- 1, and 2 +/- 1 mmHg/micron, respectively.
Functional effects of EMD-57033 in isovolumically beating isolated rabbit hearts
Authors: Tobias A. H. , Slinker B. K. , Kirkpatrick R. D. , Campbell K. B.
Published: December 2017

The results of isolated myocyte and cardiac muscle experiments indicate that inotropic agents that increase responsiveness of myofilaments to Ca2+ (so-called Ca2+ sensitizers) may prolong myocardial contraction and increase diastolic tone, but the importance of these effects in the whole heart is unclear. Therefore, we studied the effects of the Ca2+ sensitizer EMD-57033 (EMD) on left ventricular (LV) contractile events and passive properties in isovolumically beating isolated rabbit hearts that were buffer perfused at 30 degrees C. Several LV pressure and timing variables were evaluated, including the passive pressure-volume relationship, the Frank-Starling relationship, and the wall stress dependence of the duration of relaxation during perfusion with 0, 2, and 4 microM EMD. EMD (2 microM) increased average peak developed pressure of the Frank-Starling relationship by approximately 18%. In contrast, the peak developed pressure of the Frank-Starling relationship decreased toward control with 4 microM EMD, and therefore all the results presented pertain to 2 microM EMD. The maximum developed pressure at baseline volume was increased by approximately 19% by 2 microM EMD, and this was accompanied by an increase in contraction duration of approximately 13%, due exclusively to slowed relaxation. The relative contributions of maximal wall stress (sigma max) versus an independent negative lusitropic effect of EMD were determined at three LV volumes. At baseline volume, just less than one-half of the effect to slow relaxation was ascribable to an increase in sigma max, whereas the remainder was due to an independent EMD effect. LV passive properties were unchanged by perfusion with 2 microM EMD. We conclude that EMD is a potent inotrope in our isolated rabbit heart preparation, which has no effect on diastolic tone and causes a modest prolongation of contraction duration due to slowed relaxation. At baseline volume, approximately 50% of the slowed relaxation was ascribable to positive inotropy leading to increased sigma max, whereas the remaining approximately 50% was ascribable to a direct negative lusitropic effect of EMD. We discuss our results in terms of the current hypotheses regarding the mechanism of action of the Ca2+ sensitizers.
Right ventricular contractile protein function in rats with left ventricular myocardial infarction
Authors: De Tombe P. P. , Wannenburg T. , Fan D. , Little W. C.
Published: December 2017

We studied contractile function in cardiac trabeculae isolated from the right ventricles (RV) of rats with experimental heart failure (HF) induced by left ventricular (LV) myocardial infarction (24 wk post-MI; n = 6) and from sham-operated rats (n = 7). Sarcomere length (SL) was measured by laser diffraction techniques, and force (F) was measured by silicon strain gauge. SL was kept constant at all times by computer feedback control. HF was associated with marked LV dilation and pulmonary congestion. In intact, RV twitching trabeculae, HF was associated with a depression of the F-SL relation at extracellular Ca2+ concentration ([Ca2+]o) = 1.5 mM and a depression of the F-[Ca2+]o relation at SL = 2.0 microns. HF was also associated with a significant depression of the F-intracellular [Ca2+] relation at SL = 2.0 microns measured after chemical permeabilization of these RV trabeculae (skinned fibers). Our results suggest that reduced force development in this model of HF is due, in part, to depressed function of the contractile filaments.
Volume-related activities of sodium ion transporters: multinuclear NMR studies of isolated rat hearts
Authors: Askenasy N. , Navon G.
Published: December 2017

The present study aims to determine the volume-related activities of sodium ion transporters in the rat heart. Intracellular volumes were measured in isolated hearts by 1H of water and 59Co nuclear magnetic resonance (NMR) of the extracellular marker cobalticyanide. Inhibition of the Na-K-adenosinetriphosphatase pumps with 50 microM ouabain did not affect the extent of cellular swelling during 30 min of ischemia: cells swelled by 0.37 ml/g dry wt compared with the controls (0.38 ml/g dry wt). After perfusion with 400 microM ouabain or 200 microM iodoacetate, the cells shrank during ischemia (from 2.50 +/- 0.06 to 2.20 +/- 0.09 and 2.28 +/- 0.07 ml/g dry wt, respectively). Inhibition of passive sodium ion transporters reduced cellular swelling during ischemia: pretreatment (10 min) with 100 microM furosemide (Na-K-2Cl cotransport), 1.5 microM ethylisopropylamiloride (Na/H antiport), and 50 microM lidocaine (sodium channels) led to swelling of 0.27, 0.21, and 0.13 ml/g dry wt, respectively. The extent of cellular water accumulation was apparently correlated with the onset and maximal force of the ischemic contracture, unlike the data of hearts treated with ouabain and iodoacetate. The blockage of each of the passive sodium transporters improved the recovery of intracellular volumes at reperfusion, indicating that in the heart these pathways are responsible for the sustained reperfusion cellular edema. It is concluded that acute cellular swelling during myocardial ischemia is not caused by insufficiency of the Na-K pumps but is partially mediated by systems that transport sodium into the cells.
Shear-dependent release of venular nitric oxide: effect on arteriolar tone in rat striated muscle
Authors: Boegehold M. A.
Published: December 2017

This study was designed to determine whether shear-dependent changes in venular nitric oxide (NO) production can influence nearby arteriolar tone and whether this mechanism contributes to functional arteriolar dilation in contracting muscle. In resting spinotrapezius muscle of anesthetized rats, occlusion of one branch of an arcade venular bifurcation with divergent flow caused flow and wall shear rate in the parallel branch to increase by an average of 99 and 72%, respectively. After 10–30 s, the paired arcade arteriole dilated by an average of 30%, with a correlation between the increase in venular shear rate and the magnitude of arteriolar dilation. During muscle contraction, arcade arterioles dilated by 73–97% and arcade venular shear rate increased by 48–83%. The NO synthase inhibitor NG-monomethyl-L-arginine greatly attenuated arteriolar dilation to increased venular shear rate in resting muscle but did not affect arteriolar dilation in contracting muscle. These findings suggest that a shear-dependent increase in venular NO release can dilate nearby arterioles, but this mechanism is not important for the sustained dilation of these arterioles during functional hyperemia.
Regulation of ANG II-receptor subtype and its gene expression in adrenal gland
Authors: Du Y. , Guo D. F. , Inagami T. , Speth R. C. , Wang D. H.
Published: December 2017

We have previously demonstrated that two isoforms (AT1A and AT1B) of the angiotensin II (ANG II) type 1 (AT1) receptor exist in the rat kidney and are differentially regulated by a low-sodium diet. The present experiment was designed to test the hypothesis that sodium deficiency upregulates AT1A and AT1B gene expression in the adrenal gland by activating the AT1 receptor. Wistar rats (7 wk old) were divided into four groups (n = 10 each) and fed normal sodium (0.5%; NS), NS plus 3 mg.kg-1.day-1 losartan (DUP-753; i.e., DUP), low sodium (0.07%; LS), and LS plus DUP. After 2 wks, body weight and mean arterial pressure were not different (P > 0.05). Northern blot analysis showed that the ratio of AT1A: glyceraldehyde 3-phosphate dehydrogenase (GAPDH) mRNA in the adrenal gland was increased (P < 0.001) by 172% in LS but was unchanged in NS + DUP and LS + DUP vs. NS. The ratio of adrenal AT1B:GAPDH mRNA was increased (P < 0.001) by 245% in LS and unchanged in NS + DUP and LS + DUP vs. NS. Radioligand binding indicated that AT1 receptors (fmol/mg protein) in the adrenal gland were increased in LS (141 +/- 17; P < 0.001) vs. NS (54 +/- 3), NS + DUP (43 +/- 5), and LS + DUP (56 +/- 6). We conclude that sodium deficiency increases both AT1A and AT1B gene expression and elevates the AT1 receptor density in the adrenal gland. Blockade of the binding of ANG II to the AT1 receptor by losartan prevents the increases in AT1A and AT1B mRNA expression and the AT1 receptor density induced by sodium depletion, suggesting that these changes in the adrenal gland are mediated by activation of the AT1 receptor. These results will provide a basis for future experiments to further elucidate transcriptional regulation or functional activity of each of the receptor subtypes.