5-HT1A RECEPTOR BLOCKADE INCREASES PENILE ERECTIONS INDUCED BY INDIRECT SEROTONIN AGONISTS

INDIRECT serotonergic agonists, whether promoters of 5-HT release such as fenfluramine (5 mg kg(-1)) or inhibitors of 5-HT uptake such as fl uoxetine (10 mg kg(-1)), elicited in rats penile erections at a modest but significant level. Their effects were markedly potentiated by the beta-blocker tertatolol, (0.6-5 mg kg(-1)) which 5-HT1A receptor bloc king activity, but not by the beta-blocker labetalol (6.25 and 25 mg k g(-1)), which lacks such activity. In addition, tertatolol, but not la betalol, potentiated penile erections induced by meta-chloro-phenylpip erazine (1 mg kg(-1)). Thus, it appears that increasing serotonergic t ransmission increases only moderately penile erections because of the functional opposition exerted by 5-HT1A (inhibition) and 5-HT1C (activ ation) serotonin receptors on this response.