Histological Microstructure and In Vitro Mechanical Properties of Postmenopausal Ewe Perineal Body With and Without Estrogen Replacement Therapy

The objective was to assess the regional variability, mechanical properties, and histological composition of the perineal body in postmenopausal ewes with and without delayed estrogen replacement therapy (ERT), providing data relevant for pelvic floor modeling and the understanding of menopausal tissue changes.

The fibromuscular layer of the central tendon of the perineal area between the rectum and vagina was used for the study. We analyzed 24 specimens from 8 postmenopausal ewes with ERT (initiated 180 days after ovariectomy and continued for 100 days)—POST-ERT group—and 21 specimens from 7 ewes without ERT—POST group, all 280 days after ovariectomy. Uniaxial tensile tests determined the Young’s moduli in small (E₀) and large (E₁) deformation regions, ultimate stress, and ultimate strain. Histological stereology quantified volume fractions of collagen, elastin, smooth muscle, skeletal muscle, and adipose tissue in three regions (R1–R3). Group comparisons and regional analyses were performed using nonparametric statistics.

Mechanical parameters did not differ significantly between groups (E₀: 28/25 kPa; E₁: 0.38/0.33 MPa; ultimate stress: 0.23/0.23 MPa; ultimate strain: 0.94/0.90 for POST-ERT/POST). ERT was associated with higher collagen (33% versus 23%, p < 0.001) and elastin (6% versus 5%, p < 0.01) content. Regional differences were minimal, with only modest variation in adipose and smooth-muscle fractions and ultimate stress between the midline and lateral regions.

Despite prolonged estrogen deprivation, the perineal body maintained mechanical integrity. Structural changes, particularly increased collagen and elastin after delayed ERT, suggest adaptive remodeling but do not translate into measurable biomechanical reinforcement within the studied timeframe. The results provide parameters for finite element modeling of pelvic floor disorders.