Biomedical subjects

G J Grover

Publications and source records attributed to G J Grover.

At least 91 records · Page 5Linked to original sources

PubMed1992

Role of endothelin-1 and big endothelin-1 in modulating coronary vascular tone, contractile function and severity of ischemia in rat hearts.

The effect of endothelin-1 (ET-1) and big ET-1 on coronary flow and contractile function was determined in isolated nonischemic and ischemic rat hearts. Both ET-1 (IC50 = 12 pMol) and big ET-1 (IC50 = 2 nMol) reduced coronary flow in a concentration-dependent manner, although ET-1 was > 100-fold more potent. Both compounds decreased contractility, an effect which was lost when coronary flow was held constant, indicating that ET-1 and big ET-1 decrease contractility secondary to reducing coronary flow. Mechanical reduction in coronary flow to levels equivalent to those seen for ET-1 or big ET-1 caused similar reductions in contractility. Both 30 pMol ET-1 and 10 nMol big ET-1 pretreatment significantly reduced the time to contracture in globally ischemic rat hearts, suggesting a proischemic effect. Phosphoramidon (100 microM, endothelin-converting enzyme inhibitor) and BQ-123 (0.3 microM, ETA receptor antagonist) abolished the preischemic increase in coronary perfusion pressure induced by big ET-1 as well as its proischemic effect, whereas only BQ-123 abolished the cardiac effect of ET-1. Neither phosphoramidon nor BQ-123 had an effect on severity of ischemia when given alone. Phosphoramidon was also given i.v. to rats subjected to coronary occlusion and reperfusion and was found to significantly reduce infarct size 24 hr postischemia. Thus, in isolated rat hearts, big ET-1 appears to be converted to ET-1 and is a potent coronary constrictor.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1991

The combined antiischemic effects of the thromboxane receptor antagonist SQ 30,741 and tissue-type plasminogen activator.

The thromboxane-receptor antagonist, SQ 30,741, may be used as adjuvant therapy for thrombolysis and has also been shown to have antiischemic activity that is independent of its thrombolytic activity. Since tissue-type plasminogen activator (t-PA) and SQ 30,741 may be administered simultaneously, we determined whether the antiischemic effects of SQ 30,741 can be potentiated by t-PA. This was accomplished by combining doses of t-PA and SQ 30,741, which alone were not cardioprotective. Anesthetized dogs were subjected to left circumflex coronary artery occlusion for 90 minutes and reperfusion for 5 hours. The dogs were treated during reperfusion with a dose of t-PA that caused approximately a 30% reduction in plasma fibrinogen alone or in combination with 1.5 mg/kg + 0.4 mg/kg/hr SQ 30,741, which started 10 minutes after initiation of ischemia. At these doses, neither t-PA nor SQ 30,741 alone significantly reduced infarct size (57% +/- 6%, 50% +/- 10%, 57% +/- 6% of the left ventricular area at risk for vehicle controls, t-PA, and SQ 30,741 respectively); however, combination treatment resulted in a significant reduction in infarct size (37% +/- 5% of the left ventricular area at risk). Higher doses of t-PA and SQ 30,741 alone significantly reduced infarct size. The protective effects of t-PA and SQ 30,741 occurred without altering peripheral hemodynamic status. No differences in collateral or reperfusion blood flow were observed between groups. Thus although SQ 30,741 may act to improve the efficacy of thrombolysis, t-PA may in turn enhance the antiischemic activity of SQ 30,741 or at least reduce the threshold dose.

Animals↗

PubMed1991

Thromboxane A2 receptor blockade improves contractile function following cardiopulmonary bypass in dogs and pigs.

Thromboxane A2/prostaglandin endoperoxide (TP) receptor antagonists have been reported to decrease the extent of myocardial damage after coronary ligation. The purpose of this study was to determine if the TP antagonist SQ 30,741 can protect myocardial tissue during cardiac arrest and cardiopulmonary bypass (CPB) in dogs and pigs. In the first part of the study, anesthetized dogs were subjected to normothermic CPB (37.5 degrees C) at a flow rate of 2 liters/m2/min. Dogs were treated with either 5 mg/kg + 5 mg/kg/hr SQ 30,741 or vehicle starting before CPB. The aorta was cross-clamped for 25 min and then released to allow reperfusion. In another study, pigs had hypothermic (28 degrees C) CPB but with arrest for 1 hr. Myocardial recovery was assessed by segment shortening as determined by sonomicrometry. Canine hearts treated with SQ 30,741 had a significantly improved reperfusion contractile function such that at 60 min postreperfusion, segmental shortening returned to 96% of pre-bypass levels vs 70% in vehicle-treated controls (P less than 0.05). In pigs, 70% of vehicle-treated pigs could not be weaned off CPB and died. All six pigs treated with SQ 30,741 survived. SQ 30,741 prevented platelet loss in dogs, but did not in pigs. Thus, SQ 30,741 significantly improved reperfusion function in hearts subjected to CPB.

Animals↗

PubMed1991

Specific block of the anti-ischemic actions of cromakalim by sodium 5-hydroxydecanoate.

The potassium channel activators cromakalim and pinacidil were recently shown to have anti-ischemic properties in isolated globally ischemic rat hearts. The effects of two reported blockers of ATP-sensitive potassium channels, glibenclamide (glyburide) and sodium 5-hydroxydecanoate, on the anti-ischemic efficacy of cromakalim were determined in this model. Buffer-perfused rat hearts were subjected to 25 minutes of ischemia followed by 30 minutes of reperfusion. Pretreatment of these hearts with 60 microM cromakalim significantly decreased indexes of contractile function but caused a significant improvement of postreperfusion function and a significant decrease in release of lactate dehydroxygenase and in end-diastolic pressure. Pretreatment with glibenclamide at concentrations that reversed the preischemic effects of cromakalim (0.05 and 1.0 microM) also significantly reversed its postischemic protective effects. Sodium 5-hydroxydecanoate (100 and 300 microM) had no effect on the preischemic (negative inotropic) effects of cromakalim but completely reversed its cardioprotective effects. Sodium 5-hydroxydecanoate did not reverse the cardioprotective effects of the calcium entry blocker diltiazem. In phenylephrine-contracted rat aorta, glibenclamide (0.1-10 microM) inhibited cromakalim-induced relaxation, whereas sodium 5-hydroxydecanoate (10-1,000 microM) had no effect. Similarly, the ability of cromakalim to shorten cardiac action potential duration in guinea pig papillary muscle and to increase outward whole-cell potassium currents in isolated myocytes was inhibited by glibenclamide, whereas sodium 5-hydroxydecanoate was without effect. Thus, both glibenclamide and sodium 5-hydroxydecanoate inhibited the effects of cromakalim after reperfusion; however, sodium 5-hydroxydecanoate, unlike glibenclamide, had no effect in nonischemic preparations. These results suggest that sodium 5-hydroxydecanoate is an ischemia-selective inhibitor of ATP-sensitive potassium channels.

Animals↗

PubMed1991

Effects of different angiotensin-converting enzyme (ACE) inhibitors on ischemic isolated rat hearts: relationship between cardiac ACE inhibition and cardioprotection.

We determined the relationship between cardiac angiotensin-converting enzyme (ACE) inhibition and anti-ischemic efficacy of several structurally different ACE inhibitors or their prodrug esters perfused through the isolated rat heart. Seven ACE inhibitors inhibited cardiac ACE to varying degrees due to differences in uptake during perfusion through nonischemic rat hearts. Zofenopril-sulfhydryl and fosinoprilic acid were the most effective of the free inhibitors. Among the prodrugs, zofenopril and S-benzoylcaptopril, hydrolyzed rapidly by cardiac esterase, were more effective than their component ACE-inhibitors, whereas fosinopril, ramipril and enalapril were poorly active. For studies in ischemic rat hearts, vehicle or drug treatment was initiated 10 min before a 25-min period of global ischemia and during a 30-min reperfusion period. Of five unesterified ACE inhibitors studied for anti-ischemic activity, only captopril and zofenopril-sulfhydryl were found to improve postischemic contractile function and reduce cell death in the isolated rat hearts. Fosinoprilic acid, ramiprilat and enalaprilat were not cardioprotective at high perfusion concentrations, despite the fact that nearly complete inhibition of cardiac ACE was achieved with all of the compounds studied. The S-benzoyl prodrugs of zofenopril-sulfhydryl and captopril were at least as potent as their component ACE inhibitors in reducing ischemic-reperfusion damage in the same model. Neither zofenopril nor captopril, however, had any effect on coronary flow before or after ischemia. Thus, it appears that the cardioprotective effects of zofenopril and captopril are independent of cardiac ACE inhibition or, at least, that ACE inhibition alone is not sufficient. Both captopril and zofenopril are sulfhydryl-containing compounds whereas the inactive compounds are not; and, thus, this group appears to be important in mediating their cardioprotective actions.

Angiotensin-Converting Enzyme Inhibitors↗

PubMed1991

Effect of potassium channel blockade on the anti-ischemic actions of mechanistically diverse agents.

The ATP-sensitive potassium channel opener, cromakalim, protects ischemic hearts and its effect can be reversed by glyburide. It is presently unknown if glyburide can abolish the anti-ischemic effects of mechanistically different agents or if blockers of other potassium channels can abolish the protective effects of cromakalim. Thus, the effect of glyburide on previously reported cardioprotective agents was tested in globally ischemic/reperfused isolated rat hearts. Calcium antagonists, sodium channel blockers and calmodulin antagonists were found to significantly improve postischemic contractile function and reduce lactate-dehydrogenase release after 25 min of global ischemia and 30 min of reperfusion. Glyburide did not reverse their cardioprotective effects. 5-(N,N-dimethyl)amiloride, an inhibitor of Na+/H+ exchange, significantly reduced lactatedehydrogenase release without improving postischemic contractile function, and glyburide did not reverse this. The potassium channel opener, cromakalim, protected ischemic rat hearts (improved recovery of contractile function and reduced enzyme release) and this was abolished by glyburide. Charybdotoxin blocks both calcium-activated potassium channels and voltage-gated potassium channels and E-4031 the delayed rectifier potassium channels. Neither was found to effect the action of the potassium channel opener, cromakalim. These data indicate that glyburide is selective in that it only blocks the anti-ischemic effects of potassium channel openers and not other cardioprotective compounds. In addition, cromakalim is unaffected by blockers of other potassium channels, further indicating selectivity of glyburide for ATP-sensitive potassium channels.

Animals↗

PubMed1991

Cardioprotective effects of the potassium channel opener cromakalim: stereoselectivity and effects on myocardial adenine nucleotides.

We determined if the cardioprotective effects of the potassium channel opener cromakalim are stereoselective and if it can preserve adenine nucleotides in ischemic myocardium. We subjected isolated isovolumically beating rat hearts to 25 min of global ischemia and reperfusion with and without pretreatment by cromakalim or its enantiomers. All of these compounds significantly increased preischemic coronary flow with the (3S,4R)-(-)-enantiomer being more potent (EC25 = 0.52 microM) compared to cromakalim (EC25 = 1.04 microM) and the (3R,4S)-(+)-enantiomer (EC25 greater than 100 microM). The (-)-enantiomer was also significantly more potent in reducing ischemic/reperfusion damage compared to cromakalim and its (+)-enantiomer. Reperfusion contractile function was improved significantly and lactate dehydrogenase release was reduced by these compounds. Time to contracture was also increased significantly by the (-)-enantiomer (EC25 = 2.27 microM), cromakalim (EC25 = 4.89 microM) and the (+)-enantiomer (EC25 greater than 100 microM). We determined if cromakalim, in a concentration which does not depress cardiac function (10 microM), can preserve high energy phosphates during ischemia in isolated rat hearts. Cromakalim significantly preserved ATP at 15 to 25 min of ischemia. Adenylate energy charge was also significantly improved by cromakalim at 20 to 25 min into an ischemic episode. Thus, the cardioprotective effects of cromakalim are stereoselective and may be due partly to preservation of myocardial energy reserves. It is significant that cromakalim can preserve adenine nucleotides despite its lack of negative inotropic effects.

Adenine Nucleotides↗

PubMed1990

Reduction of ischemic damage in isolated rat hearts by the potassium channel opener, RP 52891.

Potassium channel activators have been shown to protect ischemic myocardium. We studied the ability of the novel potassium channel activator, RP 52891, to also reduce ischemic damage in isolated globally ischemic rat hearts. RP 52891 (1-100 microM) was given before the hearts were subjected to 25 min of ischemia and 30 min of reperfusion. Before ischemia, RP 52891 reduced contractile function only at the highest concentration (100 microM). Significant reductions in ischemic damage were observed at 3 microM and higher concentrations. RP 52891 improved reperfusion contractile function and reduced lactate dehydrogenase release. Contracture was significantly reduced by RP 52891 during reperfusion. The protective effects of RP 52891 were completely reversed by glyburide and sodium 5-hydroxydecanoate, both blockers of ATP-sensitive potassium channels. Thus, RP 52891 has direct cardioprotective efficacy, which may be related to activation of ATP-sensitive potassium channels.

Adenosine Triphosphate↗

PubMed1990

The thromboxane receptor antagonist SQ 30,741 reduces myocardial infarct size in monkeys when given during reperfusion at a threshold dose for improving reflow during thrombolysis.

The threshold dose of the selective thromboxane receptor antagonist SQ 30,741 for increasing reflow during thrombolysis was identified and then evaluated in a model of myocardial ischemia with reperfusion. In anesthetized cynomolgus monkeys, stenotic carotid arteries were occluded with a platelet-rich thrombus by electrical stimulation and recanalized with streptokinase (680 U/min intraarterially for 1 h) and heparin (200 U/kg + 120 U/h intravenously for 3 h). Concurrent administration of SQ 30,741 (2.1 mg/kg + 0.5 mg/kg per h intravenously for 3 h; n = 4) enhanced the extent of reflow 174% compared with saline solution (n = 4; p less than 0.05) during the third hour, when lower doses were ineffective. This threshold dose was tested in anesthetized African green monkeys subjected to 90 min of left circumflex coronary artery occlusion and 5 h of reperfusion. SQ 30,741 (n = 8) or saline solution (n = 11) was administered 2 min before reperfusion and continued throughout reperfusion. The heart was removed on termination of reperfusion and perfused in vitro with Evans blue and triphenyltetrazolium chloride dyes to stain tissue at risk and infarcted tissue, respectively. The percent of left ventricle at risk did not differ between saline- (37 +/- 4%) and SQ 30,741-treated (35 +/- 3%) monkeys. In contrast, infarcted tissue expressed as percent of the left ventricle at risk was less (p less than 0.01) in monkeys receiving SQ 30,741 (31 +/- 2%) than in those receiving saline solution (49 +/- 5%).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1990

Myosin light-chain phosphorylation and vascular resistance in canine anterior tibial arteries in situ.

Two regulatory systems are believed to control the contractile state of vascular smooth muscle in vitro. In one, crossbridges are phosphorylated by myosin light-chain (MLC) kinase; these phosphorylated crossbridges are believed to predominate during force development. In the other system, the crossbridges are unphosphorylated (latchbridges); the latchbridges are thought to prevail during force maintenance. The role of these systems in the control of vascular resistance in vivo is unknown. This study compared MLC phosphorylation with vascular tone in canine anterior tibial arteries in vitro and in situ. The arteries were frozen at various times before and during stimulation with norepinephrine. Under both conditions, the levels of MLC phosphorylation were low at rest and increased transiently during norepinephrine stimulation. This increase was associated with stress development in vitro and with an increase in vascular resistance in situ. Thus, the biochemical changes measured in arteries in situ parallel those measured in vitro suggesting that the in vitro models are appropriate and useful for studying the physiological function of blood vessels. To our knowledge, this is the first demonstration of changing levels of MLC phosphorylation in an artery in situ.

Anesthesia↗

PubMed1990

The protective effects of cromakalim and pinacidil on reperfusion function and infarct size in isolated perfused rat hearts and anesthetized dogs.

The direct myocardial protective effects of intracoronary infusions of cromakalim and pinacidil were determined in an anesthetized canine model of coronary occlusion and reperfusion. The left circumflex coronary artery was occluded for 90 minutes and reperfused for 5 hours, at which time the infarct size was determined. Cromakalim (0.1 micrograms/kg/min) or pinacidil (0.09 micrograms/kg/min) were infused into the left circumflex coronary artery starting 10 minutes preischemia. Cromakalim significantly reduced infarct size as a percent of the left ventricular area at risk (25 +/- 5%) compared with vehicle controls (55 +/- 7%). Pinacidil did not reduce infarct size at an equimolar dose, but at the higher dose also significantly reduced infarct size. Collateral blood flow was not significantly altered by either drug, though reperfusion flow was significantly higher in cromakalim-treated animals, particularly in the subepicardial region. When the same dose of cromakalim was given starting 2 minutes before the initiation of reperfusion, no significant beneficial effect of cromakalim was observed. In another study, isolated buffer-perfused rat hearts were subjected to 25 minutes of global ischemia and 30 minutes of reperfusion. These hearts were treated with 7 microM cromakalim, either starting 10 minutes before ischemia or only during reperfusion, and its effect on reperfusion function and LDH release were determined. Cromakalim pretreatment (both when given throughout the experiment and when not present in the reperfusion buffer) resulted in significant improvements in the reperfusion function. Reperfusion contracture and LDH were also significantly reduced with this treatment. When given only during reperfusion, cromakalim did not reduce the severity of ischemia when compared with vehicle controls. Thus, both cromakalim and pinacidil reduce ischemic/reperfusion injury, though the timing of treatment may be important.

Animals↗

PubMed1990

Nicorandil improves postischemic contractile function independently of direct myocardial effects.

We determined whether any of the antiischemic effects of nicorandil were due to direct cardioprotective effects such as potassium channel activation or to its peripheral hemodynamic effects. Nicorandil was administered either intravenously (i.v.) or directly into the ischemic coronary artery (i.c.) and compared with i.c. cromakalim (a potassium channel activator previously shown to improve reperfusion function directly in rat hearts) or vehicle for their ability to improve postischemic contractile function as measured by ultrasonic crystals in anesthetized dogs or in isolated perfused rat hearts. In a model of 25-min global ischemia and reperfusion in isolated perfused rat hearts, nicorandil (10-100 microM) did not improve reperfusion function or decrease LDH release, although 300 microM nicorandil did protect the hearts. Cromakalim (7 microM) significantly improved reperfusion function and reduced lactate dehydrogenase (LDH) release. In the dog studies, the left anterior descending coronary artery (LAD) was occluded for 15 min and was reperfused for 3 h. Nicorandil improved reperfusion function only when administered i.v., although i.c. cromakalim was efficacious in improving function. Neither nicorandil nor cromakalim improved collateral flow, although cromakalim significantly improved preischemic and reperfusion blood flows, particularly in the subepicardial region. Although i.c. treatment with cromakalim and nicorandil did not result in significant changes in peripheral hemodynamic status, i.v. nicorandil reduced both preload and afterload. Thus, at the dose used, nicorandil does not appear to have direct myocardial protective effects and the beneficial effects of nicorandil do not appear to be related to potassium channel activation in the myocardium. Potassium channel activation by cromakalim does result in direct cardioprotective effects whereas nicorandil appears to be dependent on peripheral actions for its efficacy.

Animals↗

PubMed1990

Anti-ischemic activity of the novel benzazepine calcium antagonist SQ 31,486.

We tested the benzazepine, SQ 31,486 for its ability to selectively block the voltage-dependent calcium channel and to protect the ischemic myocardium. SQ 31,486 was found to be a selective calcium antagonist in vascular tissue with an IC50 value of 1.5 microM in KCl-contracted rabbit aorta. SQ 31,486 decreased contractile function and increased coronary flow in nonischemic isolated rat hearts in a concentration-dependent manner. SQ 31,486 also significantly reduced postischemic lactate dehydrogenase (LDH) release and end-diastolic pressure (EDP) compared to vehicle. Reperfusion double product [heart rate (HR) x left ventricular developed pressure (LVDP)] was also significantly improved by SQ 31,486. Diltiazem was a less potent anti-ischemic agent and was significantly more cardiodepressant relative to its anti-ischemic efficacy than was SQ 31,486. Thus, SQ 31,486 should have a larger therapeutic index. In a model of pacing-induced myocardial ischemia in anesthetized, open chest dogs, SQ 31,486 reduced pacing-induced ST-segment elevation approximately 50% at 10, 40, and 70 min after drug administration. This protective effect occurred despite a lack of effect of SQ 31,486 on ischemic regional blood flow and peripheral hemodynamic status.

Animals↗

PubMed1990

Ruthenium red improves postischemic contractile function in isolated rat hearts.

The effect of ruthenium red (inhibitor of mitochondrial calcium entry) on reperfusion contractile function and enzyme release was determined in isolated perfused rat hearts and compared with that of diltiazem. The hearts were made ischemic for 25 min and reperfused for 30 min. They were pretreated with 1-10 microM ruthenium red, 1 microM diltiazem, or vehicle. All concentrations of ruthenium red significantly improved reperfusion contractile function without affecting lactate dehydrogenase (LDH) release or contracture. Diltiazem significantly improved reperfusion function and reduced LDH release and contracture formation. Ruthenium red still improved function even when given only during reperfusion. Diltiazem increased reperfusion oxygen consumption and efficiency of oxygen utilization whereas ruthenium red improved efficiency without an increase in oxygen consumption. Diltiazem significantly increased reperfusion functional reserve in these hearts, although ruthenium red did not. Ruthenium red reduced coronary flow and contractile function in nonischemic myocardial tissue and the reduced function appeared to be secondary to the reduced coronary flow as well as to a direct negative inotropic effect. Thus, ruthenium red improved reperfusion contractile function and oxygen efficiency; this may be related to its ability to block mitochondrial calcium uptake.

Animals↗

PubMed1990

Pharmacologic profile of cromakalim in the treatment of myocardial ischemia in isolated rat hearts and anesthetized dogs.

The detailed antiischemic pharmacology of the potassium channel activator cromakalim was determined in isolated globally ischemic rat hearts and a canine model of coronary occlusion and reperfusion. Cromakalim significantly improved reperfusion function in rat hearts starting at a concentration of 1 microM; this effect peaked at 7 microM. No cardiodepressant effects were observed in nonischemic tissue with cromakalim until a concentration of 100 microM was achieved, and this effect was reversed by glyburide. The antiischemic effect of 7 microM cromakalim was also completely reversed by glyburide and the novel ATP-sensitive potassium channel blocker sodium 5-hydroxydecanoate (5-HD). Glyburide did not reverse the antiischemic effects of 1 microM diltiazem. Cromakalim not only improved reperfusion contractile function in rat hearts, but improved the functional reserve and efficiency of O2 utilization. In anesthetized dogs, intracoronary cromakalim (0.1 micrograms/kg/min given throughout ischemia and reperfusion) significantly reduced infarct size in hearts subjected to 90-min coronary occlusion and 5-h reperfusion. Along with this reduced infarct size, the frequency of ectopic beats and the proportion of animals fibrillating during reperfusion were significantly reduced by cromakalim. In isolated globally ischemic and reperfused rat hearts, cromakalim was significantly profibrillatory. Thus, cromakalim is significantly cardioprotective, and may have the propensity for profibrillatory activity, although this is not true under all conditions.

Anesthesia↗

PubMed1990

Comparative anti-ischemic effects of dihydropyridine calcium antagonists in isolated perfused rat hearts: relationship of cardiodepression and cardioprotection.

A comparison was made of the anti-ischemic effects of dihydropyridine calcium antagonists in isolated globally ischemic rat hearts. Pretreatment with amlodipine, nifedipine, nitredipine, or nisoldipine reduced reperfusion enzyme (lactate dehydrogenase) release and contracture after 25 min of global ischemia and 30 min of reperfusion. Increasing concentrations of all compounds resulted in proportionally smaller reductions in the severity of ischemia, with larger decreases in nonischemic tissue contractility occurring. Reperfusion function was significantly improved at 30 min with nifedipine only; however, at 60 min reperfusion function was significantly improved for all except nisoldipine. Washout data from nonischemic hearts (rate of disappearance of cardiodepressant effects) showed that the dihydropyridines washed out in the following order (fastest to slowest): nifedipine greater than nitrendipine greater than nisoldipine greater than amlodipine. Thus, these dihydropyridines are anti-ischemic, though at higher concentrations cardiodepressant effects increase disproportionately. Differences in washout also effect the ability of these compounds to improve reperfusion function.

Animals↗

PubMed1990

Direct myocardial effects of the thromboxane A2/prostaglandin H2 agonists U-46619 and SQ 26,655 under ischemic and nonischemic conditions.

We tested the direct effects of thromboxane A2/prostaglandin endoperoxide (TP) receptor agonists and antagonists on ischemic rat hearts to determine if any significant actions of TP may be occurring in a buffer-perfused system (without blood). Buffer-perfused rat hearts were treated with the TP antagonist SQ 30,741 (0.5-1.0 microM) during 15 min of ischemia and 30 min reperfusion. SQ 30,741 had no effect on severity of ischemia. In the same model, the TP receptor agonists U-46619 (0.01-1.0 microM) and SQ 26,655 (0.1 microM) reduced coronary flow and cardiac function both before and after ischemia. The decrease in contractile function appeared to be secondary to flow decrement. Despite the flow effects, U-46619 reduced ischemia-induced lactate dehydrogenase (LDH) release and contracture, indicating some beneficial effects. Measurement of prostacyclin release during reperfusion with and without U-46619 treatment showed that U-46619 significantly increased prostacyclin production. Meclofenamate (5.0 microM) did not reverse the vasoconstrictor and cardiodepressant effects of U-46619 but completely reversed its beneficial effect on LDH release. TP receptor blockade with 1.0 microM SQ 30,741 completely reversed the flow and cardiodepressant effects of SQ 26,655 but did not reverse the beneficial effects of this compound on LDH release. Receptor binding studies using [3H]-SQ 29,548 and [3H]-U-46619 indicated that few if any TP receptors exist in myocytes. In conclusion, TP antagonists are not cardioprotective in this model, but exogenous TP receptor agonists have complex actions in buffer-perfused hearts, some of which are mediated by vascular TP receptors and others which are not.

15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5↗

PubMed1990

Effect of thromboxane receptor blockade on oxygen supply/consumption variables during reperfusion in the anesthetized dog.

The thromboxane A2/PGH2 receptor antagonist SQ 30,741 has been previously shown to reduce infarct size and to improve subendocardial reflow. The purpose of this study was to determine the effect of SQ 30,741 on reperfusion O2 supply/consumption variables. Anesthetized open-chest dogs treated with vehicle or 1 mg/kg + 1 mg/kg/hr SQ 30,741, i.v. (starting 10 min after the onset of ischemia) were subjected to 90 min left circumflex coronary occlusion and 3 hr reperfusion. Regional myocardial blood flow (radioactive microspheres) and arterial and venous O2 saturations (microspectrophotometry) were determined. Animals treated with SQ 30,741 had significantly higher subendocardial reflow at 3 hr (48 +/- 6 ml/min/100 g) compared with vehicle (27 +/- 10 ml/min/100 g). At 3 hr postreperfusion, O2 extraction was significantly higher in the reperfused region compared with the nonischemic region, although extraction was not at maximal values. O2 extraction was similar in vehicle- and SQ 30,741-treated animals despite the near doubling of reflow into the subendocardial region with SQ 30,741. O2 consumption was significantly reduced in the reperfused subendocardial region (1.65 +/- 0.9 ml O2/min/100 g) in vehicle controls compared with the nonischemic subendocardial region (10.2 +/- 2.6 ml O2/min/100 g). SQ 30,741 significantly improved subendocardial reperfused regional O2 consumption (4.03 +/- 0.41 ml O2/min/100 g) compared with vehicle and this increase was proportional to the flow increment (no change in the O2 supply/consumption ratio). SQ 30,741 is thus increasing subendocardial reflow secondary to an increase in O2 consumption and the increased O2 consumption may be due to preservation of myocardial tissue.

Animals↗