GROWTH-HORMONE SUPPLEMENTATION INCREASES SKELETAL-MUSCLE MASS OF OLD MALE FISHER 344 BROWN NORWAY RATS/

Growth hormone (GH) supplementation can increase the body weight of ol d rats, but the individual tissues affected were previously unidentifi ed. Therefore, the masses of the heart, spleen, kidney, epididymal fat pads, adn five skeletal muscles were assessed in male Fischer 344/Bro wn Norway rats (9, 20, 31 months) injected with recombinant human GH ( 0.7 mg/kg) or vehicle twice daily for 10 days. Muscle composition (fib er type, protein concentration, dry weight wet weight ratio, citrate s ynthase activity) was also evaluated. Muscle mass was increased with G H treatment, and this increment was undiminished in old age. Fiber typ e, protein concentration, and dry weight wet weight ratio were unaffec ted by GH. Citrate synthase activity declined in the plantaris and inc reased in the soleus with GH treatment. GH supplementation elevated he art and spleen mass, but not fat pad or kidney weight. The data demons trate that the capacity for GH-induced hypertrophy of skeletal muscle, myocardium, and spleen is retained during old age.