Thromboxane A2 receptor antagonist SQ29548 does not improve canine postischemic cerebral hypoperfusion

The thromboxane receptor antagonist SQ29548 was administered to mongrel dogs after an 11-min period of global cerebral ischemia to test the hypothesis that it would improve delayed postischemic cerebral hypoperfusion (PIH) during concurrent elevations in cerebral venous thromboxane B2 (TxB2), the stable metabolite of thromboxane A2 (TxA2). Immediately following an 11-min period of aortic root cross-clamping, six dogs received 0.2 mg/kg of SQ29548 intravenously followed by continuous infusion of 0.2 mg/kg/h (TRA group) and six received a saline placebo (control). Over the next 120 min, cerebral venous outflow was measured from the confluence of the sagittal and lateral sinuses, while arterial and cerebral venous samples were obtained for measurement of TxB2. Delayed postischemic cerebral hypoperfusion, confirmed in the control group (p < 0.05) (16 +/- 2.7 vs. 32 +/- 2.4 ml/min baseline), was nearly identical in the TRA group (14 +/- 0.9 vs. 30 +/- 2.5 ml/min baseline). Cerebral venous TxB2 levels rose dramatically in both groups after ischemia (3670 +/- 440 vs. 1100 +/- 350 pg/ml baseline, control and 2720 +/- 170 vs. 580 +/- 100 pg/ml baseline, TRA group) (p < 0.05). There were no significant group mean differences in any of the other hemodynamic data except mean arterial pressure (MAP) at T120 and Hgb at baseline. We conclude that postischemic intravenous administration of the thromboxane receptor-specific antagonist SQ29548 fails to improve delayed postischemic cerebral hypoperfusion and does not alter cerebral venous TxB2 release in this canine model of global cerebral ischemia.