sq-30741 and Myocardial-Infarction

The myocardial salvage efficacy of a thromboxane A2/prostaglandin endoperoxide (TP) receptor antagonist has not been previously determined in a ferret model of ischemia and reperfusion. Assessments of the reproducibility of infarct size resulting from a 90 min period of occlusion followed by 5 hr of reperfusion of the left anterior descending coronary artery in saline-treated control ferrets revealed a consistent mean level of tissue damage representing 23.1 +/- 1.4% of the left ventricle. In subsequent studies, ferrets were given the thromboxane receptor antagonist SQ 30,741 (1 mg/kg bolus and 1 mg/kg/hr infusion, i.v.) or vehicle. At this dose, SQ 30,741 significantly reduced infarct size from that measured in control ferrets by 44%. Concurrently, the drug produced a 97% inhibition of platelet TP receptors as measured by inhibition of the ex vivo platelet shape change response to U-46,619. Drug administration was not associated with measurable alterations in mean blood pressure, heart rate or the rate-pressure-product. The importance of this finding to clinical utility and the mechanism of the observed cardioprotective action, however, remain unclear. These data indicate that the ferret represents a useful model for the assessment of the myocardial salvage efficacy of TP receptor antagonists and are consistent with attenuation of ischemic myocardial damage by doses of these agents which produce > 96% TP receptor blockade.

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; Analysis of Variance; Animals; Blood Platelets; Blood Pressure; Ferrets; Heart; Heart Rate; In Vitro Techniques; Male; Myocardial Infarction; Myocardial Ischemia; Myocardium; Orchiectomy; Prostaglandin Endoperoxides, Synthetic; Receptors, Thromboxane; Reperfusion; Thromboxane A2; Vasoconstrictor Agents

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)

Topics: Animals; Chlorocebus aethiops; Female; Heparin; Macaca fascicularis; Male; Myocardial Infarction; Myocardial Reperfusion; Streptokinase; Thrombolytic Therapy; Thromboxane A2

We determined if the thromboxane A2 antagonist SQ 30,741 can reduce ultimate myocardial infarct size and reperfusion injury. Anesthetized dogs were subjected to left circumflex coronary artery occlusion for 90 min at which time reperfusion was instituted. In one study, SQ 30,741 (1 mg/kg + 1 mg/kg/hr) was given either 10 min postocclusion (n = 7) or 2 min (n = 9) before reperfusion along with their appropriate vehicle controls in a model of 90 min of occlusion and 5 hr of reperfusion. Infarct size was reduced 50% (P less than .05) when SQ 30,741 was given 10 min postocclusion and 30% (P less than .05) when given only during reperfusion. Flow reserve using maximally dilating doses of adenosine was determined 3 hr postreperfusion in vehicle (10 min postocclusion, n = 10), SQ 30,741 (10 min postocclusion, n = 6) and nonischemic (n = 5) animals. Maximal subendocardial flow was reduced during reperfusion in ischemic animals, but SQ 30,741 improved this compared to vehicle animals (400 +/- 95, 88 +/- 25 and 208 +/- 48 ml/min/100 g; nonischemic, vehicle, SQ 30,741 groups, respectively). To determine if myocardial salvage can be observed 24 hr postocclusion with SQ 30,741 or the cyclooxygenase inhibitor aspirin, dogs were given vehicle (n = 9), SQ 30,741 (10 min postocclusion up to 4 hr postreperfusion) or aspirin (n = 9, 40 mg/kg 30 min preocclusion) and infarct size was determined 24 hr postocclusion (90 min left circumflex coronary artery occlusion + reperfusion).(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Adenosine; Animals; Aspirin; Coronary Circulation; Dogs; Female; Male; Myocardial Infarction; Receptors, Prostaglandin; Receptors, Thromboxane; Reperfusion Injury; Thromboxane A2

The effect of the thromboxane A2 (TXA2) receptor antagonist SQ 30,741 on infarct size and myocardial blood flow during coronary occlusion and reperfusion was determined. In anesthetized dogs, the left circumflex coronary artery (LCX) was occluded and after 10 min a continuous infusion of SQ 30,741 (1 mg/kg + 1 mg/kg/h, i.v.) or saline was begun. After 90 min of LCX occlusion, the LCX was reperfused for 5 h and infarct size was then determined. Myocardial blood flows before, during, and after occlusion were determined using radioactive microspheres. SQ 30,741 resulted in a significant decrease in infarct size (34% +/- 6% of left ventricular area at risk) compared to controls (60% +/- 9%). Cardioprotection was also found with SQ 30,741 when infarct size was normalized for both area at risk and predrug collateral flow. The protective effect of SQ 30,741 occurred without an increase in collateral flow. At 1 h postreperfusion, subendocardial flow was significantly higher in SQ 30,741-treated animals (109 +/- 15 ml/min/100 g) compared to controls (71 +/- 16 ml/min/100 g). SQ 30,741, in the dose resulting in infarct size reduction, produced a 95% inhibition of platelet TXA2 receptors throughout the experiment as measured by dose-dependent inhibition of the ex vivo platelet shape change response to U-46,619, a TXA2 mimetic. Thus, a dose of SQ 30,741 that results in TXA2 blockade also results in myocardial salvage without changes in collateral flow.

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; Animals; Blood Platelets; Coronary Circulation; Coronary Disease; Dogs; Female; Hemodynamics; Male; Myocardial Infarction; Myocardial Reperfusion; Oxygen Consumption; Prostaglandin Endoperoxides; Prostaglandin Endoperoxides, Synthetic; Receptors, Prostaglandin; Thromboxane A2