Estrogen Replacement Regulates Vaginal Innervations in Ovariectomized Adult Virgin Rats: A Histological Study

Abstract

Background. Our previous Gräfenberg spot findings confirmed that the distal-third areas of the anterior vaginal wall bore a significantly greater number of nerves and sexual hormone may have certain degree of influence on these significant differences. However, the role of estrogen in vaginal innervations remains controversial. Methods. To investigate whether hormonal-neural interactions occur in the vagina, sixty rats were randomly divided into six groups: Sham-operated, ovariectomy, and 4 treatment groups. After 2 weeks of treatment, vaginal biopsies were prepared with hematoxylin and eosin and PGP9.5 using immunohistochemistry. Results. The density of small nerve fibers was significantly higher in the distal-half areas of intact vaginal walls than the proximal-half areas (P = 0.001). In contrast, the overall PGP 9.5-ir fiber innervation density was significantly decreased in the OVX rats subjected to surgical menopause. Sustained estrogen administration for 2 weeks resulted in nerve fiber proliferation, with values reaching normal levels in the low-dose estradiol valerate group. Conclusion. Our findings indicate that systemic hormonal therapy with low-dose estradiol valerate is effective and safe for treating deficient vaginal innervation caused by low level of estrogen activity in menopausal women and may aid studies to identify an optimal estradiol dose to provide relief from vaginal discomfort.

Figure 1

Immunohistochemical photomicrographs of sections taken from vaginal tissues. Sections were obtained from rats in SHAM group (a), OVX group (b), E1 (0.4 mg/kg/d (c)), E2 (0.8 mg/kg/d (d)), E3 (1.6 mg/kg/d (e)), and E4 (3.2 mg/kg/d (f)). Pan-neuronal marker PGP9.5 immunostaining: small nerve fibers are indicated by small blue arrows. The scale bar in (a)–(f) represents 50 μm (200x magnification).

Figure 2

The effects of estrogen on vaginal innervation in rats. (a) Pan-neuronal marker PGP9.5 immunostaining: vaginal tissue sections from lamina propria layer of SHAM group rats. Nerve bundles are indicated by white arrows, while small nerve fibers are indicated by small blue arrows. Scale bar represents 30 μm (400x magnification). (b) Quantitative analysis of nerve density in the rats' vagina: the Sham-operated (SHAM), the ovariectomy (OVX), E1 (0.4 mg/kg/d), E2 (0.8 mg/kg/d), E3 (1.6 mg/kg/d), and E4 (3.2 mg/kg/d) groups. N = 10 for each group. ∗ for P < 0.05; ∗∗ for P < 0.01; ∗∗∗ for P ≤ 0.001 versus SHAM group (control group) and ### for P < 0.001 versus OVX group (model).