EFFECTS OF GROWTH HORMONE ON THE METABOLISM OF THE ISOLATED LEVATOR ANI MUSCLE OF THE RAT

Abstract

The effects of growth hormone (GH) were investigated in the levator ani muscle and the diaphragm from hypophysectomized and from normal male rats. GH was added to the incubation media and/or injected daily for four days to the rats before the in vitro experiments. GH, added in vitro, stimulated the rate of accumulation of D-xylose-¹⁴C in the two muscles from hypophysectomized but not from normal rats. GH, in vitro, increased the distribution ratio of α-aminoisobutyric acid-¹⁴C (AIB-¹⁴C) in the diaphragm from hypophysectomized rats to a much higher degree than in muscles from normal rats. In vivo injections of GH to hypophysectomized rats which were not stimulating in itself, made the diaphragm insensitive to GH added in vitro. In the levator ani muscle, however, a different effect was obtained on the AIB-¹⁴C distribution ratio. GH in vitro did not stimulate muscles from hypophysectomized rats more than those from normal rats. Furthermore, administration of GH to hypophysectomized rats, which not was stimulating in itself, gave an additional effect with GH in vitro in this muscle. The accumulation rate as well as the incorporation into protein of glycine-³H increased in both muscles from hypophysectomized rats after in vivo as well as in vitro administration of GH. The results are discussed in connection to our present knowledge of the different effects of GH.