Vasodilatory effects of okadaic acid on the canine cerebral artery

We investigated the in vivo and in vitro vasodilatory effects of okadaic acid, an inhibitor of protein phosphatases, in canine basilar arteries. Angiography revealed that the intracisternal injection of okadaic acid produced a long-lasting increase in the internal diameter of the canine basilar artery. The maximal increases in diameter induced by 1 and 10 nmol of okadaic acid were 23.3 +/- 13.5 and 33.8 +/- 11.9%, respectively. Okadaic acid in the concentrations of 10(-7) and 10(-6) M also exerted a dose-dependent, long-lasting relaxation without any contraction in isolated basilar arteries, even in the resting condition. Similar effects (ED50 values and maximal relaxation) were observed in arterial strips precontracted with K+, prostaglandin F2 alpha, and phorbol 12-myristate 13-acetate. These in vito and in vivo results suggest that inhibition of protein phosphatases by okadaic acid produces a vasodilation in the cerebral artery.