Systemic administration of apomorphine improves the hemodynamic mechanism of clitoral and vaginal engorgement in the rabbit

Clitoral and vaginal engorgement during sexual stimulation depend in part on the increase of arterial inflow. It has been shown that apomorphine (APO), a non-selective dopamine receptor agonist, produces penile erection by activating dopaminergic receptors in the central nervous system. Our aim was to study whether systemic administration of APO improves the hemodynamic mechanism of clitoral and vaginal engorgement in the rabbit. Female New Zealand white rabbits (3.5-4 kg, n = 6) were anesthetized. To examine sexual arousal function, the vaginal/clitoral branch of the pelvic nerve was stimulated electrically and maximal increases in clitoral intracavernosal and vaginal wall blood flows and pressures were recorded. After this APO was injected intravenously in a dose-response manner (0.05, 0.1, 0.2, 0.3 and 0.4 mg/kg) and nerve stimulation was performed after each dose. Changes In nerve-stimulated increase of clitoral intracavernosal and vaginal blood flows and pressures after APO was compared to those recorded before APO. Electrical stimulation of the vaginal/clitoral branch of the pelvic nerve significantly increased clitoral intracavernosal and vaginal wall blood flows in the rabbit. Intravenous administration of APO caused concentration dependent increase in nerve stimulation-induced peak clitoral intracavernosal and vaginal wall blood flows reaching to statistically significant at the concentration of 0.1 and 0.2 mg/kg. Intravenous administration of APO greater than 0.2 mg/kg (0.3 and 0.4 mg/kg) were less effective or produced adverse effects on clitoral intracavernosal and vaginal wall blood flows. Intravenous APO also tended to increase nerve-stimulated increase of clitoral intracavernosal and vaginal wall pressures, but the effect was not statistically significant. In conclusion, our studies suggest that systemic administration of APO may improve clitoral and vaginal engorgement by increasing clitoral intracavernosal and vaginal wall arterial inflow.