Origin of thromboxane-mediated constriction due to neuropeptides in canine basilar artery.

Bradykinin, substance P and vasopressin induced a vasodilatation followed by a vasoconstriction in control perfused canine basilar arteries with endothelium. The dilatation was significantly reduced and the constriction was significantly enhanced by endothelial removal with saponin. The potentiated constriction was significantly blocked by sodium ozagrel, a thromboxane synthetase inhibitor. These results suggest that the dilatation due to these neuropeptides may depend on endothelium-derived relaxing factor, and that the augmented constriction after endothelial removal may be related to the thromboxane A2 production in cerebral arterial smooth muscles. This mechanism following the damage of endothelium might be implicated in cerebral vasospasm after subarachnoid haemorrhage.