Enhanced reactivity to vasopressin in rat basilar arteries during vasospasm after subarachnoid hemorrhage

Subarachnoid hemorrhage increases the plasma level of vasopressin, a well-known vasoconstrictor. We examined the sensitivity to vasopressin in rat basilar artery after subarachnoid hemorrhage using a rat subarachnoid hemorrhage model. Vasospasm was observed 1-2 days after subarachnoid hemorrhage induction, and the contractile response to vasopressin in rat basilar arteries was assessed. The concentration-response curve for vasopressin in subarachnoid hemorrhage (1 day) rats shifted leftward compared with that of control rats. The concentration-response curve for vasopressin V1 receptor agonist also shifted leftward and upward compared with that of control rats. The concentration-response curve for vasopressin was inhibited not by vasopressin V2 receptor antagonist but by vasopressin V1 receptor antagonist. Thus, it was demonstrated that the vasoconstricting effect of vasopressin was significantly enhanced in the vasospasm phase after subarachnoid hemorrhage.