GROWTH-HORMONE ADMINISTRATION TO AGED RATS IMPROVES MEMBRANE ELECTRICAL-PROPERTIES OF SKELETAL-MUSCLE FIBERS

Decreased secretion of growth hormone (GH) during aging may play a rol e in the impairment of muscle performance. To test this hypothesis we evaluated the effects of a chronic treatment with 150 mu g/kg of GH on membrane electrical properties of extensor digitorum longus muscle of 23-month-old Wistar Kyoto female rats. We found that such treatment c ould partially but significantly reduce the age-related changes of the se parameters. Indeed, with respect to untreated age-matched control r ats we found a complete restoration of fiber diameter to the adult val ue, and a partial improvement of membrane resistance and capacitance v alues. Furthermore, the GH treatment significantly increased the low t otal membrane conductance characterizing aged muscle fibers. The incre ase of total membrane conductance was due to a significant increase to ward the adult value of chloride conductance. In addition, the muscles from OH-treated aged rats had values of potassium conductance complet ely restored down to the adult ones. Accordingly, membrane excitabilit y was also significantly improved by the treatment. The same treatment in adult female rats produced a slight but significant increase of bo th chloride conductance and potassium conductance, whereas in adult ma le rats we observed only a significant increase of fiber diameter. Our data show that impairment of GH secretion may contribute to the age-r elated changes of membrane electrical properties of skeletal muscle an d support the potential benefit of GH administration to improve muscle performance in aged subjects.