Age-associated impairments in tissue strength and immune response in a rat vaginal injury model.

Abstract

Surgical repair of pelvic organ prolapse often includes native tissue repair during which the patient's own vaginal connective tissue is used to achieve pelvic support. This method, based on plication and suspension often yields suboptimal anatomical outcomes, possibly due to inadequate healing of the vaginal connective tissue. We hypothesized that age might have a negative effect on the time course and tissue biomechanics of vaginal wound healing in a rat model. Fifty young (12weeks) and old (12months) female 344BN Fischer rats were subjected to a posterior midline vaginal incision. The time course of repair was determined by measuring the size of the wound on days 1, 3, 7, and 14 post-injury. These findings correlated with the immune response to injury using a marker of impaired wound healing, the inflammatory cytokine macrophage migration inhibitory factor in the vaginal muscularis. Biomechanical properties of the healed vaginal tissue were tested 30days post-injury. Wound healing was assessed on days 1, 3, 7, and 14 post-injury. On day 3 post-injury, the wounds in the young animals had all closed whereas the wounds in the old animals remained open. Furthermore, on day 7, the wound gap was still filled with granulation tissue in the old rats, whereas for the young rats, the wound area was almost indistinguishable from the non-injured area. Macrophage migration inhibitory factor was highly expressed in the vaginal epithelium and in the vaginal muscularis after injury. When compared with young animals, macrophage migration inhibitory factor levels of old rats began to rise more than 2days later and the increased tissue expression persisted for 7days longer. The breakpoint force of the healed vagina of old rats was almost 4-fold weaker than in young rats. At 30days post-injury, the healed vagina in old rats regained less of the original (healthy) force at breakpoint than the young rats. In this rat model, age impaired vaginal wound healing, which was reflected in the altered inflammatory response to injury and reduced tissue strength.