We investigated the functional and histological changes after oophorectomy in the rabbit clitoris and vagina to determine the mechanism responsible for the development of arousal disorder in postmenopausal women. Twenty mature female New Zealand white rabbits were randomly divided into three groups: control; oophorectomy; and estrogen replacement after oophorectomy. We compared the nitric oxide synthase (NOS) activity and the degree of expression of neuronal (nNOS) and endothelial NOS (eNOS) using biochemical and Western blot analysis in clitoral and vaginal tissues. Histological change of smooth muscle and collagen contents in those tissues were also compared using Masson's trichrome staining. NOS activity and the expression of nNOS and eNOS were signi®cantly increased in the oophorectomized group while there was a decrease to the level of the control group in the estrogen replacement group. Histological examination showed that oophorectomy induced a signi®cant increase in collagen and decrease in muscle content in both clitoris and vagina, while the ratio of smooth muscle content was increased signi®cantly after the estrogen replacement. Our results clearly demonstrate that estrogen de®ciency induces compensatory NOS production which may be related to decreases in muscle to collagen ratio in female rabbit genital organs.

The role of brain angiotensin II (ANG II) in mediating cardiovascular, vasopressin, and renin responses to hemorrhage was assessed in conscious spontaneously hypertensive rats (SHR) and in normotensive Wistar-Kyoto (WKY) and Wistar rats. Intracerebroventricular administration of losartan (10 micrograms) and saralasin (1 microgram.microliter-1.min-1) produced a markedly greater fall in blood pressure and a reduced tachycardia during and after hemorrhage (15 ml/kg) compared with the artificial cerebrospinal fluid control in SHR and Wistar rats but not in WKY rats. Vasopressin release after hemorrhage was also impaired, but renin release was enhanced by intracerebroventricular ANG II antagonists in SHR and Wistar rats but not in WKY rats. Losartan and saralasin produced remarkably similar effects on the cardiovascular, vasopressin, and renin responses to hemorrhage. These data suggest that brain ANG II acting through AT1 receptors plays an important physiological role in mediating rapid cardiovascular regulation and vasopressin release in response to hemorrhage. The relative importance of brain angiotensin system may vary in different strains of rate.