Effects of ovariectomy and hindlimb unloading on skeletal muscle

Female rats(7-8 mo old, n = 40) wererandomly placed into the intact control (Int) and ovariectomizedcontrol (Ovx) groups. Two weeks after ovariectomy, animals were furtherdivided into intact 2-wk hindlimb unloaded (Int-HU) and ovariectomizedhindlimb unloaded (Ovx-HU). We hypothesized that there would be greater hindlimb unloading-related atrophy in Ovx than in Int rats. In situcontractile tests were performed on soleus (Sol), plantaris (Plan),peroneus longus (Per), and extensor digitorum longus (EDL) muscles.Body weight and Sol mass were ~22% larger in Ovx than in Int groupand ~18% smaller in both HU groups than in Int rats (Ovx × HUinteraction, P < 0.05), and therewas a similar trend in Plan muscle (P < 0.07). There were main effects (P < 0.05) for both ovariectomy (growth) and hindlimb unloading(atrophy) on gastrocnemius mass. Mass of the Per and EDL muscles wasunaffected by either ovariectomy or hindlimb unloading. Time to peaktwitch tension for EDL and one-half relaxation times for Sol, Plan,Per, and EDL muscles were faster (P < 0.05) in Ovx than in Int animals. The results suggest that1) ovariectomy led to similarincreases of ~20% in body weight and plantar flexor mass;2) hindlimb unloading may haveprevented ovariectomy-related muscle growth;3) greater atrophy may have occurredin Sol and Plan of Ovx animals compared with controls; and4) removal of ovarian hormonalinfluence decreased skeletal muscle contraction times.