Aging and menopause related decline in circulating levels of estrogen has been shown to adversely affect female sexual arousal function. Our aim was to study the effects of circulating levels of estrogen on the hemodynamic mechanism of vaginal and clitoral engorgement and on the structure of the vaginal and clitoral cavernosal tissue in the rabbit.New Zealand White female rabbits (3.5 ± 4 kg) were randomly divided into three groups with ®ve rabbits in each group: control; bilateral oophorectomy; bilateral oophorectomy undergoing subcutaneous injection of estrogen (40 m mgakgaday). After 6 weeks, the serum levels of 17 b-estradiol were measured and systemic blood pressure was monitored. Vaginal and clitoral cavernosal blood ows were measured with laser Doppler¯owmeter before and after pelvic nerve stimulation. Cross sections of the clitoris and vagina were processed for histologic examination and histomorphometric image analysis.Serum level of 17 b-estradiol (pgaml; mean AE s.d.) revealed a signi®cant decrease in the oophorectomy group (25.4 AE 5.1) compared with the control (38.5 AE 7.6) and estrogen replacement (115.9 AE 57.3) groups (P`0.05). Nerve stimulation-induced peak vaginal and clitoral intracavernosal blood¯ows in the oophorectomy group (28.9 AE 16.3 and 6.1 AE 1.4, respectively) were signi®cantly less than those recorded in the control (48.9 AE 6.5 and 11.0 AE 2.4, respectively) or estrogen replacement (48.7 AE 12.2 and 10.1 AE 2.8, respectively) group (P`0.05). In histology, marked thinning of the vaginal epithelial layers, decreased vaginal submucosal microvasculature, and diffuse clitoral cavernosal ®brosis were evident in the oophorectomy group but not in the estrogen supplement and control groups. In histomorphometry, the percentage of clitoral cavernosal smooth muscle in the oophorectomy group (49.6 AE 6.2) was signi®cantly decreased compared with the control (56.8 AE 2.6) and estrogen replacement (58 AE 3.0) groups (P`0.05).Our studies show that decline in circulating levels of estrogen impairs the hemodynamic mechanism of vaginal and clitoral engorgement and leads to histopathologic changes in the vagina and clitoral cavernosal tissue. These observations suggest that decreased circulating levels of estrogen, a physiologic change in the menopausal state, may play a role in the development of female sexual arousal dysfunction.

Clitoral and vaginal engorgement during sexual stimulation depend in part on the increase of arterial in¯ow. 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 vaginalaclitoral branch of the pelvic nerve was stimulated electrically and maximal increases in clitoral intracavernosal and vaginal wall blood¯ows 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 mgakg) and nerve stimulation was performed after each dose. Changes in nerve-stimulated increase of clitoral intracavernosal and vaginal blood¯ows and pressures after APO was compared to those recorded before APO.Electrical stimulation of the vaginalaclitoral branch of the pelvic nerve signi®cantly increased clitoral intracavernosal and vaginal wall blood¯ows in the rabbit. Intravenous administration of APO caused concentration dependent increase in nerve stimulation-induced peak clitoral intracavernosal and vaginal wall blood¯ows reaching to statistically signi®cant at the concentration of 0.1 and 0.2 mgakg. Inravenous administration of APO greater than 0.2 mgakg (0.3 and 0.4 mgakg) were less effective or produced adverse effects on clitoral intracavernosal and vaginal wall blood¯ows. Intravenous APO also tended to increase nerve-stimulated increase of clitoral intracavernosal and vaginal wall pressures, but the effect was not statistically signi®cant.In conclusion, our studies suggest that systemic administration of APO may improve clitoral and vaginal engorgement by increasing clitoral intracavernosal and vaginal wall arterial in¯ow.