bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of in vitro organic nitrate tolerance on relaxation, cyclic GMP accumulation, and guanylate cyclase activation by glyceryl trinitrate and the enantiomers of isoidide dinitrate.
Authors: Bennett B M , Schröder H , Hayward L D , Waldman S A , Murad F
Published: June 2012

Previously, it was shown that the D enantiomer of isoidide dinitrate was 10-fold more potent than the L enantiomer and 10-fold less potent than glyceryl trinitrate for stimulating cyclic GMP accumulation and relaxation of isolated rat aorta. In the present study, these organic nitrates were tested for their ability to induce tolerance to organic nitrate-induced relaxation, cyclic GMP accumulation, and guanylate cyclase activation in rat aorta in vitro. To compensate for the differences in vasodilator potency, tolerance was induced by incubating isolated rat aorta with concentrations of organic nitrates 1,000-fold greater than the EC50 for relaxation. Under these conditions, the EC50 for relaxation was increased significantly for each organic nitrate and to a similar degree on subsequent reexposure. These data suggest that the potential for inducing in vitro tolerance to relaxation was the same for the three organic nitrates tested. When activation of soluble guanylate cyclase by these compounds was assessed, the enantiomers of isoidide dinitrate were equipotent, but less potent than glyceryl trinitrate, suggesting that the site of enantioselectivity is not guanylate cyclase itself. In blood vessels made tolerant to organic nitrates by pretreatment with glyceryl trinitrate, vasodilator activity, cyclic GMP accumulation, and guanylate cyclase activation were attenuated on reexposure to each organic nitrate. In addition, differences in the potency of the three organic nitrates and the enantioselectivity of isoidide dinitrate for relaxation were abolished in tolerant tissue, whereas the potency difference between glyceryl trinitrate and isoidide dinitrate for activation of guanylate cyclase was unchanged.(ABSTRACT TRUNCATED AT 250 WORDS)
Inhibition of adrenergic vasoconstriction by endothelial cell shear stress.
Authors: Tesfamariam B , Cohen R A
Published: June 2012

Isolated perfused rabbit carotid arteries were used to determine the effects of endothelial cell shear stress on the response to adrenergic nerve stimulation. Arterial segments with and without endothelium were cannulated and perfused with physiological salt solution. Adrenergic nerves were activated by transmural electrical field stimulation. Neurogenic vasoconstriction was significantly greater in segments without endothelium when compared with that of segments with endothelium. In segments with endothelium only, vasoconstriction was depressed when shear stress was increased by increasing the viscosity of the perfusate with dextran. Perfusion with methylene blue (2 X 10(-6) M), a guanylate cyclase inhibitor, increased vasoconstriction in segments with endothelium only. In the presence of methylene blue, vasoconstriction was no longer different between segments with and without endothelium, and perfusion with dextran had no effect. In a perfusion-cascade system, perfusion with dextran of donor segments with but not without endothelium caused further relaxation of a contracted bioassay ring. These results suggest that shear stress on endothelial cells modulates adrenergic vasoconstriction by augmenting release of endothelial cell-derived vasodilators.
Positive inotropic effect of calcitonin gene-related peptide mediated by cyclic AMP in guinea pig heart.
Authors: Ishikawa T , Okamura N , Saito A , Masaki T , Goto K
Published: June 2012

The mechanism of cardiac actions of rat calcitonin gene-related peptide (CGRP) was analyzed on isolated guinea pig hearts. CGRP exerted a positive inotropic effect in a dose-dependent manner on the electrically driven left atria but not on the ventricles. Immunohistochemical studies demonstrated that CGRP-like immunoreactive nerves were distributed densely in the myocardia of the atria but only sparsely in those of the ventricles. The CGRP-induced augmentation of the contraction was accompanied by the shortening of the time to peak force and the increase in the relaxation velocity. The positive inotropic response to CGRP was significantly enhanced by isobutylmethylxanthine and was attenuated by adenosine. CGRP increased the action potential amplitude and prolonged action potential duration at the level of 50% repolarization in the left atria. In the preparations, which were partially depolarized with an increase in extracellular potassium, CGRP induced slow response action potentials. These electrophysiological results indicate that CGRP causes an increase in the slow inward Ca2+ current. The cyclic AMP content in the left atria significantly increased following the addition of CGRP, the time course of which was nearly consistent with that of the augmentation of the contractile force. In the membrane preparation of the atria, the activity of adenylate cyclase was enhanced by CGRP in a dose-dependent manner. These effects of CGRP are qualitatively similar to those of beta-adrenoceptor stimulation. It is concluded that the CGRP-induced response in the guinea pig atria is attributed to the activation of adenylate cyclase via stimulation of its specific receptor and the subsequent increase in the intracellular cyclic AMP level.
Effects of acidosis on ventricular muscle from adult and neonatal rats.
Authors: Solaro R J , Lee J A , Kentish J C , Allen D G
Published: June 2012

We compared the response of ventricular muscle from adult and neonatal rats to hypercapnic acidosis. In adult muscle, acidosis caused an initial rapid fall of developed tension to 30 +/- 5% of control (mean +/- SEM, n = 6). However, tension recovered slowly to a steady state that was 56 +/- 6% of control. In neonatal muscle, acidosis caused a significantly smaller initial fall in tension to 43 +/- 3% (n = 8, p less than 0.05), but the tension then showed a subsequent slower fall to a steady state that was 29 +/- 4% of control, significantly less than in the adult (p less than 0.01). We have attempted to identify the mechanisms underlying these differences in response. In detergent-skinned myofibrils, reducing the pH from 7.0 to 6.5 caused a reduction in the pCa50 of 0.61 units in the adult muscle, but only 0.27 units in the neonatal ventricular muscle. Myofibrillar Ca2+ sensitivity in neonatal ventricular muscle is thus less susceptible to the effects of acidic pH than that of adult muscle. Since intracellular pH decreases rapidly on application of increased external CO2, these results are consistent with the finding that, initially, developed tension in neonatal muscles is less sensitive to the effects of acidosis. Sodium dodecylsulfate gel electrophoresis of myofibrillar preparations from adult and neonatal rats demonstrated differences in thin filament proteins, including troponin I, which may underlie the observed differences in Ca2+ sensitivity. In adult rat ventricular muscles, the slow recovery of tension during acidosis is associated with an increase in the amplitude of the Ca2+ transients to 263 +/- 34% of control (n = 4).(ABSTRACT TRUNCATED AT 250 WORDS)
Influences of pressure surrounding the heart and intracardiac pressure on the diastolic coronary pressure-flow relation in excised canine heart.
Authors: Satoh S , Watanabe J , Keitoku M , Itoh N , Maruyama Y , Takishima T
Published: June 2012

We investigated the change in the instantaneous diastolic left coronary pressure-flow relation (DPFR) when the pressure surrounding the heart (SHP), right heart pressure (RHP), and left heart pressure (LHP) were systematically varied. Eight excised and maximally vasodilated canine hearts placed in an air-tight chamber were used. To obtain a capacitance-free DPFR, coronary perfusion pressure was slowly decreased (about 2 mm Hg/sec) during a prolonged diastole. The zero-flow pressure (Pf = 0) and the slope of the DPFR were analyzed. The mean values of the slope did not change significantly throughout the interventions. The mean value of Pf = 0 in the control state (SHP = RHP = LHP = 0 mm Hg) was 6.0 +/- 2.0 mm Hg (mean +/- SD, n = 8), significantly higher than the venous outflow pressure, RHP (p less than 0.001), and the other two pressures (p less than 0.001). When SHP was raised to 15 and 30 mm Hg, while the other pressures remained at 0 mm Hg, the mean values of Pf = 0 increased to 20.9 +/- 2.4 and 35.6 +/- 3.1 mm Hg (p less than 0.001 and p less than 0.0005, respectively, vs. control). The mean values of Pf = 0 when only RHP was elevated to 15 and 30 mm Hg were 16.0 +/- 1.5 and 29.3 +/- 1.5 mm Hg (p less than 0.001 and p less than 0.0005 vs. control). On elevation of LHP to 15 and 30 mm Hg, the mean values of Pf = 0 were 12.0 +/- 2.8 and 17.3 +/- 3.6 mm Hg (p less than 0.01 and p less than 0.01 vs. control). When both SHP and LHP were almost evenly elevated to about 15 and 30 mm Hg, the mean values of Pf = 0 were raised to 22.0 +/- 2.9 and 35.3 +/- 3.2 mm Hg, respectively. These mean values were not significantly different from those when only SHP was elevated to the comparable levels. The observation that Pf = 0 exceeded RHP in the control state and that RHP, which was elevated above the preceding Pf = 0, was identical with the present Pf = 0 supports the vascular waterfall mechanism when RHP is low. Furthermore, the evidence that the degree of DPFR shift was almost linearly dependent on the SHP level rather than on the LHP level indicates that the pressure on the epicardial side is one of the factors that determines the pressure at the top of the vascular waterfall.
Superoxide dismutase conjugated to polyethylene glycol provides sustained protection against myocardial ischemia/reperfusion injury in canine heart.
Authors: Tamura Y , Chi L G , Driscoll E M , Hoff P T , Freeman B A , Gallagher K P , Lucchesi B R
Published: June 2012

Disagreement regarding the cardioprotective role of superoxide dismutase may relate to the use of different durations for induction of ischemic injury and reperfusion. The present study employed superoxide dismutase conjugated to polyethylene glycol (PEG-SOD), which has a half-life greater than 30 hours. Two protocols differing in the mode of administration and the duration of the reperfusion interval were used. Dogs were subjected to occlusion of the circumflex coronary artery for 90 minutes, then reperfused for 6 hours (Protocol A) or 4 days (Protocol B). The dogs received either polyethylene glycol conjugated to albumin (PEG-ALB) or PEG-SOD (1,000 U/kg). In Protocol A, treatment was administered starting 15 minutes before coronary occlusion and continued for 2 hours, terminating 15 minutes after reperfusion. Infarct size was determined 6 hours later. In Protocol B, the conjugated proteins were given 15 minutes before reperfusion and ended simultaneously with reperfusion. Infarct size was measured after 4 days. Infarct size (percentage of area at risk) in control (n = 9) and treated (n = 9) dogs in Protocol A differed between groups: 46.7 +/- 3.5% versus 28.3 +/- 2.9%, respectively (p less than or equal to 0.005); risk regions did not differ: 42.8 +/- 1.5% versus 43.8 +/- 2.1%, respectively. Myocardial salvage also was observed in Protocol B. Infarct size in control (n = 13) and treated (n = 13) groups was 44.2 +/- 2.6% versus 29.2 +/- 1.6%, respectively (p less than or equal to 0.005), with risk regions being 44.4 +/- 1.4% versus 46.0 +/- 1.6% (p = NS). Hemodynamic variables did not differ during the period of coronary artery occlusion. The respective collateral blood flows to the inner two thirds of the ischemic myocardium determined 60 minutes after occlusion were 0.05 +/- 0.01 ml/min/g and 0.06 +/- 0.04 ml/min/g (p = 0.806) for the PEG-ALB and PEG-SOD treated groups, respectively. Infarct size was related inversely to collateral blood flow in the PEG-ALB treated group. This relation shifted downward (analysis of covariance, p = 0.017). Plasma SOD activity in Protocols A sustained for 6 hours. Significant enzymatic activity was present after 4 days in Protocol B. Previous negative studies with native SOD may be related to the short half-life of its free-radical scavenging capacity, which compromises the chances of observing a protective effect after 4 days of reperfusion. The present results support our previous observations, as well as those of other investigators, demonstrating that superoxide dismutase can reduce that component of myocardial injury associated with reperfusion.
Comparative effects of hypoxia and ischemia in the isolated, blood-perfused dog heart: evaluation of left ventricular diastolic chamber distensibility and wall thickness.
Authors: Wyman R M , Farhi E R , Bing O H , Johnson R G , Weintraub R M , Grossman W
Published: June 2012

To compare the effects of hypoxia and ischemia on left ventricular (LV) diastolic function, we studied 17 isolated, isovolumic dog hearts by measuring LV diastolic chamber distensibility (LV end diastolic pressure at constant volume), wall thickness, and myocardial pH in response to hypoxia at constant coronary flow or pressure versus global ischemia (zero coronary blood flow). Hypoxic perfusates consisted of methemoglobin-containing red blood cells suspended in lactated Ringer's solution. Brief cross-clamping of the coronary perfusion line was used to assess the contribution of coronary turgor to chamber distensibility and wall thickness. With hypoxia, left ventricles showed a significant early (5 minutes) decrease in diastolic distensibility and an increase in wall thickness, at either constant coronary perfusion pressure or flow. The increase in wall thickness was independent of hypoxia-induced changes in coronary turgor. In contrast, global ischemia produced an early increase in LV diastolic chamber distensibility and a decrease in wall thickness. When global ischemia was continued beyond 60 minutes, a decrease in LV chamber distensibility developed. This diastolic contracture was not associated with an increase in LV wall thickness. Myocardial pH decreased slightly during 15 minutes of hypoxia and markedly with 15 minutes of global ischemia. Thus, LV diastolic chamber distensibility decreased during 15 minutes of hypoxia, while an increase in distensibility was seen during global ischemia of similar duration. During hypoxia, these changes were associated with increased LV wall thickness, at either constant coronary perfusion pressure or constant coronary flow. Prolonged ischemia led to diastolic contracture without an increase in wall thickness.(ABSTRACT TRUNCATED AT 250 WORDS)
Measurement of lung microvascular pressure in the intact anesthetized rabbit by the micropuncture technique.
Authors: Bhattacharya S , Glucksberg M R , Bhattacharya J
Published: June 2012

We have developed a micropuncture technique for the measurement of microvascular pressure in the intact lung of rabbit. We anesthetized 16 rabbits (halothane, 0.8%) and mechanically ventilated them through a tracheotomy. Then, we exposed the right lung by rib resection over the right anterior chest. We measured pulmonary artery, left atrial, and systemic pressures by direct catheterization and cardiac output by the thermodilution technique. For micropuncture, we stabilized the lung on a shelf and stopped ventilation for 3-4 minutes at an airway pressure of 7 cm H2O. We injected pancuronium intravenously to paralyze the diaphragm and intercostal muscles. Of the total pulmonary vascular pressure drop, 52% occurred in the microvascular segment between arterioles and venules of 20 micron diameter, 28% occurred in the arterial segment, and 20% occurred in the venous segment. We conclude that in the intact lung of rabbit, the major pressure drop occurs in the microvascular segment.
Impaired canine coronary vasodilator response to acetylcholine and bradykinin after occlusion-reperfusion.
Authors: Mehta J L , Nichols W W , Donnelly W H , Lawson D L , Saldeen T G
Published: June 2012

Previous studies indicate impairment of coronary arterial ring relaxation in response to acetylcholine (ACh) following coronary reperfusion, mediated via loss of endothelium-derived relaxing factor (EDRF). To examine if coronary vasodilator reserve is reduced following coronary occlusion-reperfusion in intact animals, 16 open-chest mongrel dogs were subjected to 1 hour of total left circumflex (Cx) coronary artery occlusion followed by reperfusion for 1 hour. Prior to Cx occlusion, coronary blood flow increased and vascular resistance decreased (both p less than or equal to 0.01) in response to ACh and bradykinin (BK). Following reperfusion, increase in Cx coronary flow in response to both vasodilators was significantly (p less than or equal to 0.01) impaired. Myocardial histology showed extensive neutrophil infiltration and capillary plugging by neutrophils in the Cx compared with the left anterior descending coronary artery-supplied myocardium. Myocardial myeloperoxidase activity was also increased in the Cx compared with the left anterior descending region (p less than or equal to 0.02). Pretreatment of four dogs with indomethacin partially reduced the vasodilator response to BK but not to ACh. However, indomethacin did not affect reperfusion-induced attenuation of BK or ACh's coronary vasodilator effects. To determine if calcium blocker verapamil would modify reperfusion-induced impairment in coronary vasodilator reserve, six dogs were treated with verapamil. Although verapamil enhanced coronary vasodilator effects of ACh and BK, it did not modify reperfusion-induced attenuation of coronary vasodilator reserve. Myocardial neutrophil accumulation and myeloperoxidase activity was also similar in control, indomethacin, and verapamil-treated dogs. These observations suggest that coronary reperfusion impairs coronary vasodilator reserve in intact dogs. This impairment is not modified by prostaglandin inhibition or by calcium blockade. Besides loss of EDRF, capillary plugging by neutrophils may contribute to the altered coronary flow reserve observed in the immediate post-reperfusion period. Furthermore, indomethacin or verapamil are not effective in modifying the reperfusion-related impairment of coronary vasodilator reserve.
Oxygen consumption and coronary reactivity in postischemic myocardium.
Authors: Laxson D D , Homans D C , Dai X Z , Sublett E , Bache R J
Published: June 2012

Coronary vascular responses in regions of reversible postischemic myocardial contractile dysfunction (stunned myocardium) were examined in chronically instrumented, awake dogs. Left anterior descending coronary artery blood flow and oxygen extraction, aortic and left ventricular pressures, and regional myocardial segment shortening were determined. Regional myocardial blood flow was measured with microspheres. Coronary reactive hyperemia and vasodilator reserve, and regional myocardial oxygen consumption were determined. Three sequential 10-minute left anterior descending coronary artery occlusions separated by 30-minute reperfusion periods resulted in progressive postischemic dysfunction so that 1 hour after the final coronary artery occlusion, myocardial segment shortening was reduced to 37% of baseline. Despite this decrease in contractile function, left anterior descending artery flow (19.6 +/- 2.6 vs. 18.4 +/- 3.0 ml/min), myocardial blood flow and the transmural distribution of flow measured with microspheres, and regional myocardial oxygen consumption were unchanged. Although the coronary vasodilator reserve in response to adenosine was unaltered (63 +/- 9 vs. 70 +/- 15 ml/min), the reactive hyperemia response to a 10-second coronary occlusion was decreased in intensity (debt repayment ratio = 474 +/- 78% vs. 322 +/- 74%; p less than 0.05) and duration (57 +/- 9.1 vs. 35 +/- 4.5 seconds; p less than 0.05), while the peak flow response was unchanged (57 +/- 6.8 vs. 60 +/- 7.1 ml/min). Thus, in the intact awake animal postischemic myocardial contractile dysfunction was not associated with decreased myocardial oxygen consumption and did not impair the normal relation between coronary blood flow and myocardial oxygen utilization. Although coronary vessels showed a normal ability to vasodilate in response to adenosine, coronary reactive hyperemia was reduced.
Pharmacokinetics and distribution of heparin-binding growth factor I (endothelial cell growth factor) in the rat.
Authors: Rosengart T K , Kuperschmid J P , Maciag T , Clark R E
Published: June 2012

Heparin-binding growth factor I (HBGF I), previously designated as endothelial cell growth factor, is a potent mitogen for endothelial cells in vitro, which may prove useful for promoting endothelial regeneration in vivo. Analysis of the pharmacokinetics and organ distribution of HBGF I is necessary before use of HBGF I as a pharmacological agent. Consequently, pharmacological studies were carried out with [125I]HBGF I in the rat. Intravenous injections of HBGF I were given with or without heparin (2.5 units/ng HBGF I). Blood concentrations of HBGF I decreased by one half 17 seconds after HBGF I bolus. This time was prolonged to 60 seconds when HBGF I was injected with heparin. The elimination half-life of HBGF I was 14 minutes in the presence of heparin. The highest concentrations of HBGF I following intravenous bolus were found in kidney, liver, and spleen, and the lowest in fat and brain. Heparin increased HBGF I concentrations in blood and all organs measured except kidney, which was significantly decreased (p less than 0.01). Intact HBGF I was recoverable from blood 5 minutes following intravenous administration. HBGF I underwent near-complete proteolytic digestion after more prolonged ex vivo incubation with rat plasma, but HBGF I was protected from proteolysis when incubations were conducted in the presence of heparin. Thus, it is feasible that HBGF I can be administered as a pharmacological agent in the presence of heparin. Further studies assessing acceleration of in vivo endothelial growth using HBGF I with heparin appear warranted.
Anti-inflammatory actions of enprofylline, a modified xanthine, in the canine forelimb.
Authors: Dobbins D E , Soika C Y , Buehn M J , Dabney J M
Published: June 2012

It has been previously reported that enprofylline (3-propyl xanthine) prevents histamine-mediated edema formation in the guinea pig lung. To further assess the potential anti-inflammatory effects of enprofylline, we infused it intra-arterially into the canine forelimb before and during a local intra-arterial infusion of histamine (4 micrograms/min) while monitoring forelimb skin lymph parameters. Infusion of enprofylline at 2 mg/min significantly decreased forelimb arterial pressures and increased heart rate and pulse pressure. Subsequent infusion of histamine caused a further reduction in forelimb arterial pressures and an increase in lymph flow, protein concentration, and protein transport similar to that seen with the infusion of histamine alone. Infusion of enprofylline at 5 mg/min decreased forelimb arterial pressures and systemic pressure. Subsequent histamine infusion further reduced forelimb arterial pressures, but the increase in lymph parameters was markedly attenuated. Enprofylline infused at 10 mg/min also decreased forelimb arterial and systemic pressures, but subsequent histamine infusion was essentially without effect on lymph parameters. To assess the role of catecholamines in enprofylline-mediated attenuation of histamine edema formation, we infused enprofylline at 5 mg/min in the presence of a beta 2-receptor blockade produced by the intra-arterial infusion of ICI 118551. The effects of enprofylline and histamine on vascular pressures were similar to those seen in the absence of beta 2-receptor blockade, but lymph flow, protein concentration, and protein transport increased similar to that seen with histamine alone. These data indicate that enprofylline is capable of attenuating histamine-induced increases in microvascular permeability, but this action of enprofylline is of an indirect nature, mediated through the release of catecholamines.
Long-term versus intrabeat history of ejection as determinants of canine ventricular end-systolic pressure.
Authors: Sugiura S , Hunter W C , Sagawa K
Published: June 2012

We studied the effect of ejection on end-systolic pressure in isolated heart preparations. Ejecting beats were compared with isovolumic beats having the same volume as at end systole. While holding end-systolic volume constant, various stroke volumes, including negative stroke volumes (volume injected during systole), were imposed using a predetermined volume command. After switching contraction mode between ejecting and isovolumic, we measured the immediate and steady changes in end-systolic pressure. In the first isovolumic beat after switching from steady-state ejecting beats, the change in end-systolic pressure was variable, depending on the stroke volume. The end-systolic pressure of the ejecting beat exceeded that of the isovolumic beat on average by up to 18 mm Hg with small stroke volume, but the ejecting end-systolic pressure became lower than isovolumic with either large stroke volume (stroke volume/end-systolic volume less than 0.96) or with negative stroke volume. During the transient phase following a switch from ejecting to isovolumic, the end-systolic pressure gradually decreased to a steady state. Consequently, even in steady state, ejecting end-systolic pressure exceeded isovolumic pressure over a significant range of stroke volume (stroke volume/end-systolic volume less than 1.18). After returning contraction mode from isovolumic back to ejecting, we observed responses that were a mirror image. These results indicated that in addition to negative uncoupling effect, ejection exerts positive effects on ventricular end-systolic pressure that are manifest both quickly and gradually. We hypothesized that the mechanism responsible for the positive effect is length-dependent activation via the larger volume (both at the initiation of contraction and averaged over a cardiac cycle) of a beat that ejects compared to one held isovolumic at end-systolic volume. The results with volume injection were consonant with this concept.
Basic polyamino acids rich in arginine, lysine, or ornithine cause both enhancement of and refractoriness to formation of endothelium-derived nitric oxide in pulmonary artery and vein.
Authors: Ignarro L J , Gold M E , Buga G M , Byrns R E , Wood K S , Chaudhuri G , Frank G
Published: June 2012

The objective of this study was to elucidate the mechanism by which polyamino acids containing L-arginine, L-lysine or L-ornithine cause endothelium-dependent relaxation of bovine intrapulmonary artery and vein. Basic but not acidic or neutral polypeptides ranging in average molecular weights from 17 to 225 kDa elicited time- and concentration-dependent relaxation and cyclic GMP accumulation in precontracted rings of artery and vein by endothelium-dependent mechanisms. Vascular responses were markedly inhibited by oxyhemoglobin, methylene blue, or potassium. The basic polyamino acids stimulated the formation and/or release of an endothelium-derived relaxing factor (EDRF) identified as nitric oxide (NO) in perfused segments of both artery and vein as assessed by bioassay. The polyamino acids and A23187 released a similar endothelium-derived NO (EDNO) from artery and vein, as assessed by the similar half-life (3-5 seconds), antagonism by superoxide anion or oxyhemoglobin, enhancement by superoxide dismutase, and lack of influence by indomethacin. The basic polyamino acids elicited potent relaxant responses with EC50 values ranging from 3 x 10(-9) to 2 x 10(-7) M, and a direct correlation was obtained between molecular weight and relaxation potency irrespective of the basic amino acid incorporated. Prolonged contact of arterial or venous rings with basic polyamino acids resulted in the rapid development of marked refractoriness to relaxation and cyclic GMP formation on addition of polyamino acid. Moreover, refractoriness developed to the vascular responses of other endothelium-dependent vasodilators but not to glyceryl trinitrate or isoproterenol. The mechanism of refractory responses was attributed to interference with EDNO formation and release as assessed by bioassay and chemical assay. The hypothesis is forwarded that the basic polyamino acids serve as partial substrates for the enzyme system that catalyzes the conversion of L-arginine to NO. Prolonged contact between substrate and enzyme results in enzyme desensitization and the development of refractoriness or a form of tolerance to vasodilators whose action is mediated by EDNO.
Importance of venodilatation in prevention of left ventricular dilatation after chronic large myocardial infarction in rats: a comparison of captopril and hydralazine.
Authors: Raya T E , Gay R G , Aguirre M , Goldman S
Published: June 2012

In rats with large myocardial infarctions, we compared the effects of captopril, a presumed arterial and venous vasodilator, with hydralazine, which is thought primarily to be an arterial vasodilator. To determine if the effects of captopril were dependent on the pathophysiological consequences of heart failure, we also studied a group of noninfarcted rats treated with captopril. In noninfarcted rats treated with captopril, left ventricular (LV) systolic and mean aortic pressures decreased from 132 +/- 12 to 107 +/- 15 mm Hg and 122 +/- 1 to 100 +/- 2, respectively (p less than 0.01). In noninfarcted rats, captopril decreased LV weight, LV weight/body weight, and total heart weight/body weight but produced no effects on the peripheral venous circulation. Rats subjected to coronary artery ligation were selected by ECG criteria to have large myocardial infarctions and were treated for 4 weeks with captopril (n = 8), hydralazine (n = 5), or placebo (n = 9). In infarcted rats treated with captopril, LV systolic, mean aortic pressures and LV end-diastolic pressure (LVEDP) decreased (p less than 0.01) from 115 +/- 4 to 86 +/- 3 mm Hg, 106 +/- 4 to 74 +/- 3 mm Hg, and 23 +/- 2 to 11 +/- 2 mm Hg, respectively. Mean circulatory filling pressure decreased (p less than 0.05) from 11.2 +/- 0.6 to 8.7 +/- 0.8 mm Hg and venous compliance increased (p less than 0.05) from 2.04 +/- 0.07 to 2.70 +/- 0.20 ml/mm Hg/kg. Blood volume decreased (p less than 0.05) from 67.3 +/- 0.9 to 58.2 +/- 1.8 ml/kg.(ABSTRACT TRUNCATED AT 250 WORDS)
Pressor hormones regulate atrial-stretch-induced release of atrial natriuretic peptide in the pithed rat.
Authors: Ruskoaho H , Vakkuri O , Arjamaa O , Vuolteenaho O , Leppäluoto J
Published: June 2012

Atrial wall stretching is a known stimulus for atrial natriuretic peptide (ANP) secretion. The effects of the stimulation of autonomic nervous system, hemodynamic factors, and humoral factors (epinephrine, angiotensin, vasopressin, and brain extracts) on the release of ANP under basal conditions and during increased atrial pressure produced by acute volume loading in pithed rats were examined. In conscious rats, acute volume expansion by 0.9% of saline (4 ml) increased the plasma immunoreactive ANP (IR-ANP) concentrations by a factor of 4 (140 +/- 30 pg/ml vs. 521 +/- 140 pg/ml, p less than 0.001, n = 8), whereas volume-induced ANP release was blocked in pithed rats (75 +/- 9 pg/ml vs. 99 +/- 13 pg/ml, NS, n = 7). The ANP versus right atrial pressure curve shifted to the right, indicating that much smaller amounts of IR-ANP were released in pithed than in conscious rats for each given increase in right atrial pressure. Electrical vagal and sympathetic nerve stimulation or changes in heart rate had no effect on plasma IR-ANP concentrations and failed to restore the volume-load-induced release of ANP in pithed rats. When extracts of anterior pituitary lobe, brain cortex, or hypothalamus were infused, no effect on volume-expansion-induced plasma IR-ANP levels was seen. In contrast, acute volume expansion caused a fourfold increase in levels of circulating IR-ANP in pithed rats that received posterior pituitary extracts, and the ANP versus right atrial pressure curve shifted markedly to the left. Infusion of a V1 antagonist blocked the volume-expansion-induced ANP release produced by the posterior pituitary extract. When [Arg8]-vasopressin (0.025 or 0.05 micrograms/kg/min) was infused to pithed rats, mean arterial pressure increased but basal plasma IR-ANP did not change significantly. However, acute volume expansion in the presence of vasopressin infusion (0.05 micrograms/kg/min) increased the amount of circulating IR-ANP by a factor of 4 (113 +/- 14 pg/ml vs. 414 +/- 43 pg/ml, p less than 0.001, n = 8). Thus, for a given increase in right atrial pressure, a similar amount of IR-ANP was released in the pithed rat during the vasopressin infusion as in the normal conscious animal. V1 antagonist blocked the increase in mean aterial pressure as well as the increase of plasma IR-ANP produced by [Arg8]-vasopressin. In addition, volume expansion during intravenous epinephrine (1.75 micrograms/kg/min) and angiotensin (1.0 micrograms/kg/min) doubled plasma IR-ANP levels.(ABSTRACT TRUNCATED AT 400 WORDS)
Cardiac sympathetic afferent cell bodies are located in the peripheral nervous system of the cat.
Authors: Bosnjak Z J , Kampine J P
Published: June 2012

Studies of the stellate ganglion and middle cervical ganglion indicate that sympathetic efferent nerve activity can be modified by peripheral excitatory inputs and that these neural connections may function as pathways for a peripheral reflex at the level of the thoracic sympathetic ganglia. This excitatory synaptic input could have a soma in either the central or the peripheral nervous system. A study was designed to determine whether chronic decentralization (3 weeks) of the stellate ganglion in cats would 1) abolish sympathetic cardiac afferent nerve activity recorded at the stellate cardiac nerve and 2) abolish local thoracic reflexes that are generated by stimulation of peripheral nerves. The ansae subclaviae, T3 and T4 rami, and stellate ganglion were also examined by electron microscopy for the extent of Wallerian degeneration. Afferent cardiac activation of the axon collaterals arising from cell bodies located in the dorsal root ganglia was abolished due to degeneration. However, sympathetic afferent nerve activity from the left ventricular receptors was still present and was recorded from the stellate cardiac nerve in all cats. Cardiac receptors were sensitive to mechanical distortion, increases in the left ventricular pressure, and epicardial application of veratrine hydrochloride. These data imply that 1) cardiovascular afferent input to the stellate ganglion persists following chronic decentralization and 2) the sensory neurons are located in the peripheral sympathetic nervous system. Thus, we find that regulation of the heart occurs in part via thoracic ganglia, independently of the central nervous system.
Role of thromboxane A2 in the control of myocardial O2 supply/consumption balance and severity of ischemia during pacing-induced ischemia.
Authors: Grover G J , Parham C S
Published: June 2012

The role of thromboxane A2 (TXA2) in the control of O2 supply/consumption variables during pacing-induced ischemia was examined using the TXA2 receptor antagonist SQ 29,548. Anesthetized, open-chest dogs were subjected to left anterior descending coronary artery (LAD) stenosis that produced significant epicardial S-T segment elevation (12 mV) only when superimposed on atrial pacing. Regional myocardial blood flow was determined using radioactive microspheres, and O2 consumption was determined by measuring O2 saturation of venous blood draining the ischemic region. The dogs were treated with saline or 0.2 mg/kg + 0.2 mg/kg/hr SQ 29,548, and the effect on ischemia was determined during 5-minute pacing-induced ischemic episodes at 10, 40, and 70 minutes postdrug or saline treatment. SQ 29,548 significantly reduced S-T elevation at 40 and 70 minutes postdrug compared with saline values and at all times measured compared with its paired predrug pace+stenosis values. SQ 29,548 reduced S-T elevation approximately 45% compared with its paired predrug values at 70 minutes. SQ 29,548 resulted in a significantly higher subendocardial-to-subepicardial flow ratio (0.70 +/- 0.10, p less than 0.05) compared with saline-treated animals (0.42 +/- 0.06), with an overall increase of flow to the ischemic region of approximately 40%. This increased flow was matched by a proportional increase in O2 consumption without a change in O2 extraction. The O2 supply/consumption balance was also unchanged by SQ 29,548 implying that despite the increase in blood flow, the ischemic region was still flow-limited.(ABSTRACT TRUNCATED AT 250 WORDS)
Significance of the transmural diminution in regional hydrogen ion production after repeated coronary artery occlusions.
Authors: Warner K G , Khuri S F , Marston W , Sharma S , Butler M D , Assousa S N , Saad A J , Siouffi S Y , Lavin P T
Published: June 2012

Previous studies have revealed that the regional accumulation of ischemic metabolites including hydrogen ion (H+) and PCO2 diminish after repeated occlusions. We postulated that this diminution reflects a blunted metabolic response that is related to the severity of ischemic injury and, hence, may be most pronounced in subendocardial (ENDO) regions. To investigate this hypothesis, the left anterior descending coronary artery was serially occluded three times in 51 dogs for a period of either 3 minutes (n = 15), 5 minutes (n = 18), or 15 minutes (n = 18). Each occlusion was separated by 45 minutes of reperfusion. Myocardial [H+] was measured in the endomyocardium and in the epimyocardium of the ischemic anterior wall by use of miniature pH glass electrodes. Accumulation of H+ during occlusion (delta [H+]) in the ENDO region was significantly less during the second occlusion when compared with the first occlusion (3-minute occlusions: 28.2 +/- 3.7 nM/l vs. 39.4 +/- 5.4 nM/l, p less than 0.002; 5-minute occlusions: 49.8 +/- 5.0 nM/l vs. 72.1 +/- 6.5 nM/l, p less than 0.0002; 15-minute occlusions: 132.3 +/- 14.6 nM/l vs. 225.6 +/- 27.7 nM/l, p less than 0.0003). A similar trend was noted for delta [H+] in the subepicardial (EPI) regions. During occlusion, the rise in [H+] occurred sooner, and delta [H+] was consistently greater in the ENDO when compared with the EPI regions (p less than 0.05). Regional myocardial blood flow did not change during the three occlusions, indicating that the diminution in H+ accumulation stemmed from a decrease in H+ production and not from an increase in collateral flow. The decrement in H+ accumulation between the first and second occlusions (delta [H+]1-delta [H+]2) 1) was greater in the ENDO than in the EPI regions (p less than 0.05); 2) correlated with the duration of occlusion (ENDO: r = 0.66, p less than 0.001; EPI: r = 0.82, p less than 0.0001); and 3) was related to the impairment of anterior wall systolic shortening after the first reperfusion period. These findings suggest that the diminution in H+ production that follows serial coronary occlusions reflects a blunted metabolic response that is related to both the duration of ischemia and the degree of systolic dysfunction. Moreover, though attenuation of ischemic metabolite production occurs transmurally, it is most pronounced in the deep ENDO regions.
Longitudinal propagation of contraction in the isolated conduit coronary arteries of humans and pigs.
Authors: Araki H , Sakaino N , Furusho N , Nishi K
Published: June 2012

We examined the longitudinal propagation of contraction in isolated human and pig coronary arteries. Epicardial coronary arteries of about 2 cm were cut open longitudinally, and the tension development of circular muscles was measured simultaneously at three sites (both cut ends and the midportion of the segment). Cyclic tension changes arising at one site of human coronary artery propagated smoothly to the other sites, and the whole length of segment worked as a single unit. Contraction induced by locally applied prostaglandin F2 alpha or histamine also propagated in four of seven preparations. The remaining three human and all seven pig coronary arteries showed propagation of such drug-induced contraction after treatment with 10 mM tetraethylammonium (TEA). In pig coronary arteries treated with TEA, electrical stimulation evoked a reproducible local contraction and its propagation. Propagation velocity was 9.0 +/- 0.7 at 0.8 mM calcium concentration and increased to 11.1 +/- 0.9 and 13.1 +/- 1.4 mm/sec as calcium concentration rose to 1.8 mM and 7.2 mM, respectively. Local contraction did not propagate at calcium concentrations of 0.2 mM or less. The calcium antagonist diltiazem decreased the propagation velocity dose dependently and blocked propagation of contraction at 0.3 microM without significant effects on the magnitude of local contraction. We conclude that smooth propagation of contraction develops in epicardial coronary arteries of humans and pigs and that the propagation may depend on calcium influx.
High molecular weight proteins purified from cardiac junctional sarcoplasmic reticulum vesicles are ryanodine-sensitive calcium channels.
Authors: Rardon D P , Cefali D C , Mitchell R D , Seiler S M , Jones L R
Published: June 2012

The cardiac high molecular weight proteins/ryanodine receptors were purified to homogeneity from junctional sarcoplasmic reticulum membranes and shown to exhibit large conductance calcium channel activity. High molecular weight proteins were solubilized from junctional sarcoplasmic reticulum in zwitterionic detergent and purified by size-exclusion chromatography followed by sucrose density gradient centrifugation. The purified proteins exhibited an apparent Mr = 400,000-350,000, and bound [3H]ryanodine with a Kd of 4.6 nM and a Bmax of 140-280 pmol/mg protein. High molecular weight proteins demonstrated divalent cation channel activity after incorporation into planar lipid bilayers. Two channel types were identified. Large conductance channels had a slope conductance of 96 +/- 13 pS and a Erev of 42 +/- 9 mV (n = 5); small conductance channels had a slope conductance of 5.5 +/- 1 pS [1.0 microM cis CaCl2; 50 mM trans Ba(OH)2]. Reducing cis calcium from 1 microM to 1 nM reduced the large conductance channel open time from 7 +/- 1% to 0.1% (holding potential, -100 mV). Adding ATP (1 mM) to the cis chamber increased channel open time from 6 +/- 1% to 52 +/- 4% (holding potential, -100 mV); 10 nM ryanodine increased and 100 microM ryanodine decreased percent of open time of the 96 pS channel, without altering unitary channel conductance. The large conductance channel was similar to the calcium release channel detected in native canine cardiac junctional sarcoplasmic reticulum vesicles. Our data suggest that the ryanodine receptor, the calcium-release channel, and the high molecular weight proteins are all identical proteins containing allosteric regulatory sites for calcium, ATP, and ryanodine.
Stimulation of aortic smooth muscle prostacyclin by serotonin: role of distinct receptors in contractile and synthetic states.
Authors: Demolle D , Van Coevorden A , Boeynaems J M
Published: June 2012

It has been shown previously that serotonin stimulates the production of prostacyclin by bovine aortic smooth muscle cells in culture, via 5-HT2 receptors (Coughlin SR, Moskowitz MA, Antoniades HN, Levine L. Proc Natl Acad Sci USA 1981;78:7134-7138). These cells express a synthetic phenotype, whereas the majority of the smooth muscle cells in the media from adult arteries are in a contractile state. We have now compared 5-HT stimulated prostacyclin production in bovine aortic media explants, a preparation of contractile smooth muscle, with cultured smooth muscle cells derived from the explants. In the 1-10 microM range, serotonin stimulates the release of prostacyclin from the explants of bovine aortic media, cultured for a short period. In the presence of cocaine (30 microM), 1 microM was sufficient to produce a maximal effect. The stimulatory action of serotonin was sustained with time and did not induce a lasting desensitization. The effect of serotonin on the explants was inhibited only partially (+/- 30%) by ketanserin, a selective and potent 5-HT2 antagonist. It was mimicked by 5-carboxamido-tryptamine, a 5-HT1 agonist, but was only weakly inhibited by methiothepin, a 5-HT1 antagonist. As expected, in cultured smooth muscle cells, 5-carboxamido-tryptamine was only a weak agonist in stimulating prostacyclin production. In conclusion, it appears that the serotonin effect on prostacyclin production is mediated by different receptors in media explants from bovine aortic media and cultured cells obtained by outgrowth from these explants: a 5-HT2 receptor in the smooth muscle cells in culture and a receptor presenting some similarities with 5-HT1 receptors in the explants.
Chronotropic responsiveness of developing sinoatrial and ventricular rat myocytes to autonomic agonists following adrenergic and cholinergic innervation in vitro.
Authors: Atkins D L , Marvin W J
Published: June 2012

The chronotropic responses of isolated sinoatrial node and ventricular muscle cells to neurotransmitters were compared in vitro with and without selective adrenergic and cholinergic innervation. Explants of either thoracolumbar sympathetic ganglion or sacrococcygeal spinal cord were added to cultures of newborn rat sinus node regions or ventricular apexes harvested before the onset of autonomic innervation in vivo. Catecholamine synthesis was detected by glyoxylic acid histofluorescence. Acetylcholine synthesis was indicated by monoclonal antibody labeling of choline acetyltransferase. After electrical or pharmacological stimulation of neurons, the chronotropic response of individual myocardial cells confirmed the presence of neuroeffector transmission; the nature of the myocyte response identified the stimulated neuron as either adrenergic or cholinergic. Chronotropic responses of all myocardial cells to norepinephrine or acetylcholine were transcribed on a recorder coupled to a video photoconductive cell monitor. Isolated sinoatrial node cells were supersensitive to norepinephrine and acetylcholine; thresholds were 3 x 10(-16) M and 6 x 10(-15) M, respectively. These sinoatrial node cells remained sensitive to both norepinephrine and acetylcholine after the development of innervation in vitro. Ventricular cells also were sensitive with thresholds of 3 x 10(-11) M and 6 x 10(-14) M to norepinephrine and acetylcholine, respectively. However, following in vitro innervation, ventricular cells were significantly less sensitive to norepinephrine and acetylcholine (thresholds 3 x 10(-9) M and 6 x 10(-11) M). These data are the first to demonstrate that neurotrophic modulation is not homogeneous throughout the myocardium and that it may be dependent on the specific myocardial cell innervated.