Presence of serotonin in the rat vas deferens: its influence on contractile responses

Serotonin has been detected in the rat vas deferens. Increase in the serotonin concentration by exposure of the rat vas deferens to L-tryptophan occurs in vitro. p-chlorophenylalanine partly blocks the increase in serotonin concentration induced by tryptophan in vitro but not in vivo. Chronic sympathetic denervation induces an increase in 5-HT concentration. Responses of the vas deferens to transmural stimulation are depressed by pretreatment of rats with p-chlorophenylalanine, and the depression is reversed by incubation in vitro with 5-hydroxytryptophan or serotonin. Serotonin can enhance the response to transmural stimulation at low concentrations but has no effect at higher concentrations. Physostigmine-induced enhancement of the response to stimulation is depressed only by higher concentrations of serotonin. The results raise the question whether endogenous serotonin can act as a modulator of neurotransmission in the rat vas deferens.