Effect of 5-hydroxytryptamine on mesenteric hemodynamics in the pig.

The superior mesenteric blood flow response to close intra-arterial infusions of 5-hydroxytryptamine (5-HT) was investigated in anesthetized pigs. Over the entire dose-range studied (0.03-30 mug.animal-1.min-1), 5-HT induced a dose dependent increase in mesenteric blood flow. Following dihydroergotamine, administered intra-arterially, the 5-HT effects were significantly blocked or attenuated. Blockade of neurotransmission, induced by tetrodotoxin, was without any significant influence on the 5-HT-induced mesenteric flow increase. The results suggest a direct effect of 5-HT on specific serotoninergic receptors in the porcine mesenteric vascular bed. An indirect effect, mediated by a local enteric nervous mechanism, could not be demonstrated.