Peripheral Modulation of Dopaminergic Receptors Affects Erectile Responses in Rats

Abstract: Clinical observations have suggested that dopaminergic mechanisms are involved in the regulation of male sexual responses, including erection. Apomorphine was initially reported to exert its erectogenic effects by modifying central dopaminergic activity. This study aimed primarily at evaluating and investigating the effect of apomorphine on erectile functions in rats and its potential effects on the cardiovascular system, as well as the possible role of dopaminergic stimulation in the peripheral control of erection. Measurement of intracavernosal pressure changes elicited by electrical stimulation of the cavernosal nerve in anaesthetized rats and mating tests were used. SCH23390, the D₁ receptor antagonist, attenuated penile response to electrical stimulation. Intravenous administration of apomorphine in low dose (100 µg/kg), but not in high dose, significantly potentiated erectile responses to electrical stimulation. Intracavernosally injected apomorphine (50 µg/kg) significantly potentiated the filling rate of the corpora cavernosa 5 min. after injection, and did not induce erection in absence of electrical stimulation. In addition, apomorphine amplified the male sexual and copulatory behaviour by reducing ejaculation, mount and intromission latencies, and significantly increasing the number of ejaculations per session. However, apomorphine produced rapid and long-lasting hypotension and potentiated the hypotension and tachycardia associated with nerve-stimulated penile erection. Our results suggest that D₁-dopaminergic receptors may be functionally involved in the peripheral mediation of penile erection. Apomorphine may amplify sexual and copulatory behaviour and may also, by a complementary role, amplify neurogenically mediated erections by acting in the periphery.