Differential modulation by the endothelium of contractile responses to 5-hydroxytryptamine, noradrenaline, and histamine in the rabbit isolated basilar artery.

1. To assess modification by endothelium, we determined the contractile responses of intact rings from rabbit basilar artery to histamine, noradrenaline and 5-hydroxytryptamine (5-HT) and compared them with Triton X-100-treated and NG-nitro-L-arginine (L-NNA)-treated preparations. 2. Among the agonists examined histamine caused the strongest contraction of vascular smooth muscles and noradrenaline the weakest one. The present results are consistent with the basal release of endothelial-derived relaxing factor (EDRF). 3. 5-HT caused a much greater modification than the one expected from basal release of EDRF, suggesting that the release is induced by 5-HT, in contrast to the previous results. Our findings also indicate that 5-HT could induce the release of both contracting factor (EDCF) and EDRF from the endothelium.