Effect of Growth Hormone on the DNA Content of Muscles of Young Hypophysectomized Rats

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Abstract
Recent studies have shown that the amount of DNA in skeletal muscles of rats increase during the early weeks of life. This increase in DNA appears to be dependent upon the pituitary gland. In view of these findings, experiments were conducted to determine if pituitary growth hormone could alter the amount of DNA in various muscles of young hypophysectomized rats. Rats were injected intraperitoneally with bovine growth hormone or saline for 1 or 7 days. When a 7 day treatment period was used, injections were given once daily. Following treatment, the amount of DNA in the rectus femoris, gastrocnemius, pectoralis major diaphragm was measured. Treatment of the animals for 1 day with growth hormone had no effect on the amount of DNA in these muscles. However, following 7 days of treatment with the hormone, the amount of DNA in each of the muscles was markedly elevated. Since there was a concomitant increase in muscle weight, the concentration of DNA in terms of [mu]g/mg of wet muscle was not altered significantly. These experiments show that growth hormone can increase the amount of DNA in skeletal muscles of hypophysectomized rats. Thus, it is likely that the increase in muscle DNA, which occurs during the normal course of growth in rats, is dependent, in some measure, upon pituitary growth hormone.