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 muscular damage and atrophy. We investigated the effect of rat growth hormone (rGH) on immobilized hindlimb muscles of 26-mo-old rats. Administration of rGH significantly reduced muscle weight loss and muscle protein oxidation caused by immobilization. Capillary blood volume, measured by photoplethysmography of the hindlimb, showed a 34% reduction in immobilized animals, which was eliminated by rGH. The activity of creatine phosphokinase in immobilized gastrocnemius muscle was significantly reduced by immobilization. This damage was diminished by rGH administration. Similarly, the increase in acid phosphatase activity in immobilized muscle was reduced after rGH treatment. Morphologically, marked muscle atrophy and fiber disorientation were observed in immobilized limbs. Therapy with rGH prevented some of these changes. These results indicate that administration of rGH may provide a useful means to attenuate the degenerative effects of limb immobilization of aged rats, as evident from physiological, biochemical, and morphological parameters.