Surgical menopause impact on vaginal mechanical properties

Menopause plays an important role in altering the biomechanical properties of the pelvic floor and the potential development of pelvic organ prolapse. There is limited evidence examining how menopause and aging impact the viscoelastic properties of vaginal tissue. Here, we used 21 female Long-Evans rats. Two cohorts were equally divided (n = 6 per cohort) to undergo Sham surgery or ovariectomy (OVX) at 3-4 months of age, and the remaining were aged to 20-24 months. We performed unconfined compression on 1 mm biopsy samples of mid-vaginal tissue subjected to stress relaxations at 5% and 10% strain, followed by a 50% compression ramp. The stress relaxation data were fit to extract the instantaneous modulus, equilibrium modulus, and relaxation time constant (tau), and the ramp test was used to estimate the tangent modulus. We found that OVX animals had an instantaneous modulus 50% and 54% smaller compared to the Sham (p = 0.007) and Aged (p = 0.0007) animals, respectively. The equilibrium modulus of the OVX and aged animals were 46% and 43% lower compared to Sham animals (p = 0.037 and p = 0.02, respectively), while Sham animals had a 30% and 40% longer tau compared to OVX (p = 0.045) and aged (p = 0.01) animals, respectively. Lastly, we found a significant difference in the tangent modulus between cohorts (p = 0.006), where we found that OVX animals had the lowest tangent modulus compared to Sham (p = 0.05) and Aged (p = 0.005) animals. Our results indicated that surgical menopause had a larger impact than chronological aging on biomechanical deterioration in rat vaginal tissue.