Body weight and leukocyte infiltration after an acute exercise-related muscle injury in ovariectomized mice treated with estrogen and progesterone.

In both rats and mice, an acute skeletal muscle injury leads to leukocyte infiltration in which the leukocytes remove dead fibers and cellular debris, induce a secondary injury, and/or promote myofiber regeneration. Short-term exogenous estrogen treatment attenuates this leukocyte infiltration and prevents body weight gain in rat exercise-induced skeletal muscle injury models. But these estrogen effects may not occur in mice because body weight gain does not consistently occur in ovariectomized mice treated with estrogen. Additionally, progesterone may also attenuate this leukocyte infiltration without affecting body weight. The aim of the current study was to compare body weight and leukocyte infiltration in exercise-injured skeletal muscle of ovariectomized mice treated with exogenous estrogen and progesterone for the short period of 17 days with that of ovariectomized-placebo-treated mice and gonadal-intact male and female mice. There was no significant difference in body weight between the ovariectomized-estrogen-treated and the ovariectomized-placebo-treated mice. The amount of intramuscular leukocyte infiltration of ovariectomized mice treated with estrogen or progesterone was not significantly different from that of ovariectomized-placebo-treated mice. However, in the injured muscle, the mean area of the leukocyte antigen, 7/4, of the ovariectomized-estrogen-treated group was 2-3-fold greater than that of the ovariectomized-placebo-treated, ovariectomized-estrogen-progesterone-treated, and intact male groups (p<.05), suggesting that the 7/4-positive leukocytes of the ovariectomized-estrogen-treated group were larger or had more antigen. In conclusion, ovariectomized mice demonstrate a different body weight and leukocyte response to short-term estrogen treatment than that of ovariectomized rats, and short-term estrogen treatment modulates leukocyte phenotype. These data broaden our understanding of estrogen's effects on body weight and leukocyte infiltration, and may aid in increasing our understanding of how males and females differ in response to acute muscle injury.