Effects of estrogen on nitric oxide synthase and histological composition in the rabbit clitoris and vagina

We investigated the functional and histological changes after oophorectomy in the rabbit clitoris and vagina to determine the mechanism responsible fo r the development of arousal disorder in postmenopausal women. Twenty matur e female New Zealand white rabbits were randomly divided into three groups. control; oophorectomy; and estrogen replacement after oophorectomy. We com pared the nitric oxide synthase (NOS) activity and the degree of expression of neuronal (nNOS) and endothelial NOS (eNOS) using biochemical and Wester n blot analysis in clitoral and vaginal tissues. Histological change of smo oth muscle and collagen contents in those tissues were also compared using Masson's trichrome staining. NOS activity and the expression of nNOS and eN OS were significantly increased in the oophorectomized group while there wa s a decrease to the level of the control group in the estrogen replacement group. Histological examination showed that oophorectomy induced a signific ant increase in collagen and decrease in muscle content in both clitoris an d vagina, while the ratio of smooth muscle content was increased significan tly after the estrogen replacement. Our results clearly demonstrate that es trogen deficiency induces compensatory NOS production which may be related to decreases in muscle to collagen ratio in female rabbit genital organs.