The role of platelets in the development of cerebral vasospasm.

A possible role of platelet-derived 5-HT was examined concerning the pathogenesis of cerebral vasospasm. Intracisternal injection of 5 ml of platelet-rich plasma (PRP; approximately 7.5 x 10(8) platelets) induced not only acute (1 h) but also chronic (7 days) angiographically evident cerebral vasospasm in dogs. Sympathetic perivascular nerves on cerebral arteries showed no remarkable change following repeated injections of PRP, as the dense distribution of catecholamine-fluorescence and neuropeptide Y-like immunoreactive nerve fibers on Day 7 was comparable to findings in the preinjection controls. While there were no 5-HT-immunoreactive fibers in the cerebral arteries of control animals, numerous 5-HT-immunoreactive fibers were present in the PRP-injected animals. These results suggest that 5-HT, presumably released from extravasated platelets, may be taken up by nerve endings and act as a vasoconstrictor transmitter in the pathogenesis of chronic vasospasm.