(110) Contractility Mechanisms of Proximal Vaginal Smooth Muscle: Effects of in Vivo Treatment With Sex Steroids in an Experimental Animal Model of Ovariectomy

Abstract Introduction The vagina is a fibromuscular organ of the female genital tract, characterized by a complex anatomical and functional organization. Although the proximal portion appears less involved in the mechanisms of the sexual response compared to the distal portion, it still plays a fundamental role in ensuring mechanical support and structural integrity. The regulation of vaginal smooth muscle activity is mainly mediated by the NO/PRKG/cGMP-dependent pathway, responsible for relaxation, and the RhoA/ROCK signalling, involved in contraction. Sex hormones play a key role in regulating these pathways and maintaining the integrity and functionality of the vaginal tissue. Objective The aim of this study was to evaluate the effects of in vivo sex hormone administration on the mechanisms of relaxation and contractility in the proximal vagina, using a validated animal model of ovariectomized (OVX) Sprague–Dawley rats. Methods Subgroups of OVX rats were treated with 17β-estradiol (E), testosterone (T) or T and letrozole (T + L) for 6 weeks and compared with a group of intact control female rats (CTL). Rat smooth muscle cells (rvSMCs) were isolated from proximal vagina of CTL animals and characterized. The mRNA isolated from proximal vagina tissue and rvSMCs was analysed by semi-quantitative RT PCR. In vitro contractility studies were performed on noradrenaline (NA)-precontracted proximal vagina strips to evaluate the relaxing response to increasing doses of acetylcholine (ACh) or sodium nitroprusside (SNP), in the presence or absence of vardenafil, a selective PDE5 inhibitor. Results The mRNA expression analysis in proximal vagina tissues and rvSMCs showed a higher expression of ERα, PR, and AR, with a significantly lower expression for ERβ and GPER1. OVX significantly reduced the mRNA expression of the NO/cGMP pathway associated genes eNOS, PRKG, GC1a3, GC1b3, and PDE5, which was restored by T treatment (alone or with letrozole) but not by E, except for an increased nNOS mRNA expression. In vitro ACh administration induced a dose-dependent relaxation significantly reduced by OVX, compared to CTL. This response was normalized by T and T + L administration, but only partially improved by E. SNP induced a dose-dependent relaxation in the CTL group that was enhanced by OVX, with E treatment showing a similar efficacy although with reduced potency. Conversely, T and T + L treatments restored the response to control levels. Interestingly, in the presence of vardenafil, SNP-induced relaxation was enhanced in the CTL group and resulted doubled in the OVX + T and OVX + T + L groups, while it was negligible in the OVX and after E supplementation. Finally, the mRNA expression of the contractile signalling associated genes RhoA, ROCK1, ROCK2, and ACTA2 was significantly reduced by OVX and restored by T administration, with or without L, but not by E. Conclusions This study has shown, for the first time, that androgen regulation plays a functional role in modulating the molecular mechanisms regulating smooth muscle relaxation/contractility in the proximal portion of the rat vagina. These findings suggest a predominant role of androgen signalling over estrogen in the physiology of the proximal vagina. Disclosure No.