EFFECT OF GROWTH-HORMONE ON GASTROCNEMIUS-MUSCLE OF AGED RATS AFTER IMMOBILIZATION - BIOCHEMISTRY AND MORPHOLOGY

Immobilization of limbs of aged animals is associated with swift muscu lar damage and atrophy. We investigated the effect of rat growth hormo ne (rGH) on immobilized hindlimb muscles of 26-mo-old rats. Administra tion of rGH significantly reduced muscle weight loss and muscle protei n oxidation caused by immobilization. Capillary blood volume, measured by photoplethysmography of the hindlimb, showed a 34% reduction in im mobilized animals, which was eliminated by rGH. The activity of creati ne phosphokinase in immobilized gastrocnemius muscle was significantly reduced by immobilization. This damage was diminished by rGH administ ration. Similarly, the increase in acid phosphatase activity in immobi lized muscle was reduced after rGH treatment. Morphologically, marked muscle atrophy and fiber disorientation were observed in immobilized l imbs. Therapy with rGH prevented some of these changes. These results indicate that administration of rGH may provide a useful means to atte nuate the degenerative effects of limb immobilization of aged rats, as evident from physiological, biochemical, and morphological parameters .