Definition: Given an abstract of a paper, generate a title for this paper such that conveys the key focus of the paper.
Input: Abstract: Subarachnoid hemorrhage has a profound effect on cerebrovascular reactivity. The present study noted a progressive change in the sensitivity and reactivity of rabbit basilar artery to serotonin after experimentally induced hemorrhage. The basilar artery exhibited an initial diminished response to serotonin for periods up to 6 hours after hemorrhage, whereafter the vessel gradually became hyperresponsive. The hypersensitivity became maximal 36 hours after hemorrhage and then began to return to normal. Such early onset of serotonin hypersensitivity and reactivity after subarachnoid hemorrhage has not been previously reported. The level of tension developed, however, suggests that serotonin alone is unlikely to cause vasospasm. The strict differentiation of spasm into early and delayed components is questioned.

Hemorrhage-induced alterations of rabbit basilar artery reactivity and sensitivity to serotonin.