Effects of Ovariectomy on Skeletal Muscle Structure and Function in Young Female Rats: Protective Effects of the Flavanol (−)‐Epicatechin

Abstract

BackgroundMenopausal women suffer from various symptoms due to estrogen deficiency. Menopause can occur as a natural progression of aging or following the surgical removal of the ovaries or their damage from treatments such as chemotherapy. In women, estrogens are known to play a key role in regulating metabolism, cardiovascular, brain and bone structure and function amongst other organs and systems. However, little is known about the impact that low estrogen levels have on skeletal muscle structure and function. The flavanol (−)‐epicatechin (Epi; which is present in large concentrations in cacao) decreases muscle fatigue and promotes skeletal muscle growth in animal models. In clinical studies, the administration of cocoa and/or Epi can (in normal subjects) enhance muscle function while limiting the organ damage seen in Becker or Duchenne muscular dystrophy patients.ObjectiveThis study aims to characterize the long‐term effects of ovarian hormone depletion on skeletal muscle (macro and microscopic) structure and function. We also wish to explore the capacity of Epi treatment to reverse the loss induced by hormone depletion in muscle mass and function.MethodsThree month old female Wistar rats were used for the experiments (n=30). Animals were allocated into 3 groups: 1) sham, 2) ovariectomized (OVX, provided water by daily gavage) and, 3) OVX plus Epi treatment (provided Epi daily by oral gavage at 1 mg/kg/day dissolved in water). Once animals were allocated into their groups, they were subjected to surgery and allowed to recover for 1 week before gavage was initiated. Over the course of 3 months, the estrous cycle, body weight, and food intake of the rats was monitored. Animals were also subjected to treadmill and front limb strength testing. At the time of euthanasia, the gastrocnemius and EDL muscle were collected as well as blood samples for biochemical and/or histological analysis.ResultsAfter 3 month of ovariectomy, rats developed significant decreases in skeletal muscle mass, loss of front limb strength (~15%) and endurance as measured by treadmill testing (~50%). Histology analysis of gastrocnemius samples demonstrated significant decreases in myofiber cross sectional area. The analysis of skeletal muscle samples by Western blots also demonstrated significant increases in the content of atrophy pathway associated proteins (MURF, ATF1, atrogin) (~30%). In blood, significant increases in circulating levels of the proinflammatory cytokines occurred (~50%). Three week of treatment with Epi was able to fully restore the loss of muscle mass. Within1 week of treatment a recovery of front limb strength was noted to occur. Terminal treadmill testing also demonstrated a full recovery of exercise capacity of ovariectomized rats treated with Epi.ConclusionsIn this study we demonstrate the significant adverse impact that reductions in ovarian hormones play on skeletal muscle structure and function. Most strikingly, Epi was able to fully reverse the deleterious effects of ovariectomy. Of interest is that Epi has been provided safely to humans and evidence protective and/or beneficial effects on muscle structure and function.