Effects of subarachnoid hemorrhage on platelet-derived vasoconstriction of rabbit basilar artery

The effects of subarachnoid hemorrhage on platelet-derived vasoconstriction of the isolated rabbit basilar artery were examined using an isometric tension recording method. The subarachnoid hemorrhage was induced by injecting arterial blood in the cisterna magna. The following points were confirmed: (1) the maximal contraction produced by the platelets (10(7)/mL) treated with indomethacin or dazoxiben (thromboxane synthetase inhibitor) were suppressed (65% or 70% of the control); (2) the contraction of the arteries treated with ONO-3708 (thromboxane A2 antagonist) or ketanserin was inhibited (73% or 8.4%), as was contraction after subarachnoid hemorrhage (67% or 14%); (3) platelet-induced contraction was potentiated after subarachnoid hemorrhage; and (4) serotonin-induced contraction was potentiated after subarachnoid hemorrhage. However, synthetic thromboxane A2-induced contraction was not potentiated. The present experiments suggest that both serotonin and thromboxane A2 contribute to vasoconstrictions induced by the platelets, before and after subarachnoid hemorrhage. The platelet-derived contraction response is potentiated after subarachnoid hemorrhage and serotonin is responsible for the increased reactivity.