Effects of estrogen on the relaxation response of rabbit clitoral cavernous smooth muscles

We investigated whether estrogen has a peripheral effect on the smooth muscle relaxation response of the clitoris, similar to that of androgens in cavernous tissues of the penis. Forty-two New Zealand White female rabbits (2.3-2.7 kg) were randomly divided into control (sham operation) and bilateral oophorectomy groups (acute and chronic groups with or without estradiol replacement). The acute and chronic groups were killed at 5 days and 12 weeks post-oophorectomy, respectively. Relaxation responses of the clitoral cavernous strips to endothelium-dependent and independent vasodilators and electrical field stimulation (EFS) were observed. Serum total cholesterol and low-density lipoprotein increased significantly and acetylcholine-induced relaxation of the clitoral strips wa significantly attenuated in the oophorectomy group with chronic estrogen deficiency but not in the chronic oophorectomy group with estradiol replacement or in the acute estrogen deficiency group. No significant differences in the relaxation responses of the cavernous strips to sodium nitroprusside or to the non-adrenergic, non-cholinergic-selective relaxation response to the EFS were found among the control, acute and chronic estrogen deficiency groups. These findings suggest that estrogen may not have a direct peripheral effect on clitoral cavernous smooth muscle relaxation. Hypercholesterolemia might be a possible explanation for the impaired endothelium-dependent relaxation of clitoral smooth muscle in chronic estrogen deficiency.