Ovariectomy, hindlimb unweighting, and recovery effects on skeletal muscle in adult rats

INTRODUCTION: The effect of female sex hormones on skeletal muscle is unclear. Reports suggest that female sex hormones have an anabolic effect, have no effect, or are detrimental to skeletal muscle. METHODS: To amplify ovarian hormones' potential effects on skeletal muscle, 6-mo-old virgin intact (sham), ovariectomized (OVX), and ovariectomized plus estrogen (OVX + E2) rats were hindlimb unweighted (HLU) for 4 wk. To investigate estrogen's influence on the recovery process, OVX-HLU, sham-HLU and OVX + E2 HLU rats were cage-recovered for 2 wk following 4 wk of HLU. Changes in muscle mass were determined for the soleus (SOL), extensor digitorum longus (EDL), quadriceps (QUAD), gastrocnemius (GAST), tibialis anterior (TA), plantaris (PLA), and flexor carpi radialis (FCR). Dry weights were determined for GAST and TA. Peak tetanic tension was ascertained in the postural SOL and locomotor PLA. RESULTS: HLU resulted in a significant (p < 0.05) decline in mass of all muscles studied except EDL and FCR. The magnitude of atrophy resulting from suspension was similar between groups including wet and dry muscle mass normalized to bodyweight. Following HLU there were no differences between intact and OVX rats for contractile characteristics. Reloading for 2 wk resulted in recovery of wet muscle mass in intact and OVX + E2 rats for SOL, PLA, GAST, QUAD, and TA and in dry mass for GAST and TA. Reloaded OVX-HLU rats failed to recover wet muscle mass in all but the SOL and failed to recover GAST and TA dry weight. For example, PLA mass values for intact (sham) rats were 350 +/- 33, 284 +/- 41, and 346 +/- 44 mg for the control, HLU, and recovery groups, respectively. PLA values for OVX rats were 378 +/- 29, 316 +/- 30, and 325 +/- 23 mg for the control, HLU, and recovery groups. DISCUSSION: Results suggest that ovarian function influences the recovery of skeletal muscle mass following a period of reduced physical activity.