Histamine potentiation of nerve- and drug-induced responses of a rabbit cerebral artery.

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Abstract
Rabbit basilar artery rings are normally relatively unresponsive to transmural stimulation of their sympathetic nerve supply. However, in the presence of histamine (0.55 muM), contractile responses to nerve stimulation were markedly increased. Norepinephrine and serotonin concentrations that produce 50% of a maximum contractile response (ED50) were considerably decreased in the presence of histamine; maximum responses to both norepinephrine and serotonin were increased. Although a prejunctional effecto of histamine has not been eliminated, potentiation of responses to transmural nerve stimulation is probably due to an increase in smooth muscle responsiveness to norepinephrine. In rabbit saphenous artery rings, histamine produced a qualitatively similar potentiation of responses to nerve stimulation, norepinephrine, and serotonin except that maximum responses were not increased. Serotonin (0.084 muM) did nog potentiate contractile responses of the basilar artery to transmural nerve stimulation or norepinephrine. Since histamine and serotonin are released from rabbit platelets in response to tissue injury the synergistic effect of these agents on vascular smooth muscle contraction might be advantageous in minimizing hemorrhage. But such a response could also be deleterious if the effects of these vasoconstrictors were prolonged.