EFFECTS OF OVARIECTOMY AND HINDLIMB UNLOADING ON SKELETAL-MUSCLE

Female rats (7-8 mo old, n = 40) were randomly placed into the intact control (Int) and ovariectomized control (Ovx) groups. Two weeks after ovariectomy, animals were further divided into intact 2-wk hindlimb u nloaded (Int-HU) and ovariectomized hindlimb unloaded (Ovx-HU). We hyp othesized that there would be greater hindlimb unloading-related atrop hy in Ovx than in Int rats. In situ contractile tests were performed o n soleus (Sol), plantaris (Plan), peroneus longus (Per), and extensor digitorum longus (EDL) muscles. Body weight and Sol mass were similar to 22% larger in Ovx than in Int group and similar to 18% smaller in b oth HU groups than in Int rats (Ovx X HU interaction, P < 0.05), and t here was a similar trend in Plan muscle (P < 0.07). There were main ef fects (P < 0.05) for both ovariectomy (growth) and hindlimb unloading (atrophy) on gastrocnemius mass. Mass of the Per and EDL muscles was u naffected by either ovariectomy or hindlimb unloading. Time to peak tw itch 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. Th e results suggest that I) ovariectomy led to similar increases of simi lar to 20% in body weight and plantar flexor mass; 2) hindlimb unloadi ng may have prevented ovariectomy-related muscle growth; 3) greater at rophy may have occurred in Sol and Plan of Ovx animals compared with c ontrols; and 4) removal of ovarian hormonal influence decreased skelet al muscle contraction times.