The effect of testosterone on skeletal muscle development and protein synthesis in rabbits

The effect of testosterone administration on muscle development and protein synthesis was studied with intact male rabbits. Rabbits were randomized into three experimental groups; day 0 control (G-1), day 15 control (G-2) and day 15 testosterone (G-3). Testosterone (delta4-Androsten-17beta-ol-3-one in silastic tubing) was surgically implanted into the G-3 rabbits. On day (G-1) and day 15 (G-2 and 3) of the experiment all rabbits were injected IP with 50 mu Ci-3H-leucine. Rabbits were sacrificed at intervals after the 3H-leucine injection. Right and left semitendinosus muscles, pituitary and adrenal glands, testicles and blood samples were obtained for analysis. Testosterone improved (P less than .01) gain and feed efficiency, depressed testicle weight (P less than .01), increased serum testosterone and insulin (P less than 0.01) but did not affect adrenal and pituitary weights. Muscle moisture, fat and total protein, myofibrillar, sarcoplasmic and stromal protein fractions and RNA and DNA content were not significantly affected by testosterone although G-3 semitendinosus muscle had the highest total and myofibrillar protein, RNA, and DNA content. The testosterone treated rabbits (G-3) had higher (P less than 0.05) 3H-leucine incorporation into myofibrillar protein and lower 3H-leucine incorporation into sarcoplasmic protein than the day 0 and day 15 controls.