Enhanced Serotonergic Transmission Stimulates Oxytocin

The involvement of serotonin (5-HT) in oxytocin secretion was investigated in this study. Pharmacologic agents that influence serotonergic transmission were administered to conscious un-restrained male rats 30 mm prior to sacrifice and plasma oxytocin concentration was measured by radioimmunoassay. The d- and I- stereoisomers of the 5-HT releaser fenfluramine significantly increased plasma oxytocin in a dose-dependent manner. Oxy-tocin secretion was more potently stimulated by d-fenfluramine than by /-fenfluramine. The 5-HT releaser p-chloroamphetamine also increased plasma oxytocin. The following 5-HT agonists increased plasma oxytocin concentration: the 5-HT1 agonist m-chlorophenyl-piperazine [1 0-20 mg/kg intraperitoneally (i.p.)], the 5-HT1 agonist 1-(2,5-dimethoxy4-l-phenyl)-2-aminopro-pane (0.5-2.0 mg/kg i.p.) and the 5-HT1 agonist 1-piperazinyl-6-chloropyrazine (1 0 mg/kg i.p.). In contrast, the 5-HT1AB agonis