Cerebral hemorrhage is the main cause of abnormal cerebral arteriolar constriction resulting in cerebral ischemia that leads to paralysis, mental and physical disabilities, and deaths. Despite progress in the diagnosis of subarachnoid hemorrhage (SAH), SAH-induced cerebral vasospasm remains one of treatable causes of morbidity and mortality in patients. The mechanism(s) by which cerebral arterial narrowing occurs following hemorrhage remain largely unknown, but modification of cerebral microvascular responses is prominent, and characterized by impaired vasodilator and increased vasoconstrictor mechanisms in cerebral arteries. Several factors may contribute to the observed alterations of pial arteriolar reactivity. Increased endothelin-1 (ET-1) production has been consistently observed and ET-1 has been implicated as a possible mediator of cerebral hemorrhage-induced vasospasm. However, the mechanism(s) by which increased ET-1 production occurs are not known. The proposed experiments are designed to test the hypothesis that by-products of hemolyzed blood clots {oxyhemoglobin (OxyHb), lysophosphatidic acid (LPA), or serotonin (5-HT)} stimulate ET-1 production via activation of protein kinase C (PKC). To test this hypothesis, two specific aims will be addressed using primary culture of cerebral microvascular endothelial cells. 1) To characterize the effects of OxyHb, LPA, or 5-HT on El-I production and 2) to determine the cellular mechanism(s) by which these vasospasmogenic agents released from blood clots stimulate El-I production. To accomplish these aims, primary cell culture, molecular biological, immunoblotting, and immunoprecipitation techniques will be employed to investigate the mechanism(s) involved in the regulation of ET-1 production by these blood by-products. The results from the proposed research will have important therapeutic implications for survivors of SAH, who experience complications that include paralysis, mental and physical derangement, loss of sight and hearing. Our understanding of the mechanisms underlying the consequences of SAH will make it possible for early and appropriate intervention to prevent or reduce these complications from hemorrhagic stroke.