Distal vagina smooth muscle contractility mechanisms: effects of in vivo sex steroids treatment in an animal experimental model of ovariectomy

Objectives The female sexual response is a complex phenomenon where multiple psychophysiological factors are involved. Sex steroids play a pivotal role in female health and sexuality. The aim of this study was to investigate the effects of sex hormones on the smooth muscle contractile mechanism in the distal vagina using a validated animal model of ovariectomized (OVX) Sprague-Dawley rats. Methods Subgroups of OVX rats were treated with 17β-oestradiol (E2), testosterone (T), or testosterone and letrozole (T+L) for 6 weeks and compared with a group of intact female rats. In vitro contractility studies were carried out on noradrenaline (NA) pre-contracted distal vaginal strips to investigate the effect of OVX and in vivo treatments on vaginal smooth muscle activity. The mRNA from vagina tissue samples was analysed by semi-quantitative RT-PCR, and membrane translocation of RhoA was evaluated by Western blot analysis. Results The dose dependent relaxion induced on NA pre-contracted vaginal strips by Y-27632, a selective ROCK inhibitor (1 nM-100 μM), was significantly decreased by OVX and restored by oestrogen, but not by T or T+L administration. The pre-incubation with NO synthase inhibitor L-NAME significantly increased the response to Y-27632 in CTRL and OVX+T groups, but not in OVX. Interestingly, OVX significantly reduced the mRNA expression of NO signalling gene PKG1, an effect counteracted by T±L but not by E2 administration, and the RhoA/ROCK pathway genes, normalized by the treatment with T±L and E2. Finally, Western blot analysis showed how, compared to controls, OVX increased the membrane translocated active form of RhoA and T treatment reverted this effect by increasing the inactive cytosolic form. E2 administration normalized the expression of the active protein. Conclusions This study confirms the beneficial effects of androgens on the well-being of the vagina supporting their therapeutic role in the treatment of genitourinary syndrome of menopause (GSM) symptoms associated to hormonal decrease.