Viscoelastic properties and muscular function of the human anterior vaginal wall

Abstract:

The aim of the study was to assess the viscoelastic properties of the isolated anterior vaginal wall and to test its tentative muscular functions in a specially designed in vitro model. Vaginal biopsies were obtained from 16 urologically healthy women not on hormonal therapy who had undergone hysterectomy because of menometrorrhagia and/or uterine fibroids. The biopsies were taken from the anterior vaginal wall during vaginal or abdominal surgical procedures. Tissues were immersed in ice-cold and oxygenated Hepes buffer. In the in vitro model, the elastic properties were evaluated from a stress-relaxation test. The muscular function was tested by stimulating the prepared vaginal strips with K⁺, noradrenaline (NE), and prostaglandin F₂α (PGF₂α). In addition, the distribution of muscle cells was analyzed histologically in cryostat sections of the vaginal strips. Under a resting tension of 20–40 mN, the vaginal strips displayed spontaneous contractile activity. The extent of relaxation initiated by stretching was greater in transverse than in longitudinal vaginal strips. Moreover, it was greater in postmenopausal than in premenopausal women (P<0.01). K⁺ (0.01–2 M) evoked contractions had caused a dose-dependent increase in basal tone of the strips. NE at concentrations of 10⁻⁶–10⁻³ M had similar effects to K⁺. PGF_2α (0.15–2.5 μM) increased the vaginal contractile activity in a dose-dependent manner. The histological examination showed that the vaginal wall studied had an inner mucosal, a middle connective tissue and an external muscular layer. In the latter both longitudinal and circular smooth muscle layers were found. It was concluded that this in vitro model can be used to interpret the viscoelastic properties and muscular function of the human anterior vaginal wall. Stressrelaxation data indicate that the ability of relaxation of tissue strips obtained from a circular direction of the female anterior vaginal wall is greater than that of strips obtained from a longitudinal direction, and that this ability is greater in postmenopausal women than in premenopausal women. Histologically the anterior human vaginal wall consists mainly of smooth muscle cells arranged in both circular and longitudinal layers. Between these layers there is connective tissue similar to that seen in other organs of the urogenital tract.