Changes in the activity of transaminases and l-glutamic acid dehydrogenase induced by growth hormone

Abstract

Summary 1. Changes in activity of l -glutamic acid dehydrogenase (GAD) and glutamic-pyruvic transaminase (Gl-Py) in liver, and of glutamic-oxal-acetic transaminase (Gl-Ox) in liver and muscle, were studied in hypophysectomized groups of rats injected with saline or growth hormone for 0, 2, 5, or 10 days, and in corresponding groups of sham-operated rats. 2. Hepatic GAD activity was slightly but significantly higher in hypophysectomized rats than in sham-operated ones, and was not altered by growth hormone in either group. 3. In sham-operated rats, hepatic Gl-Py activity was unaffected by growth hormone in the dose employed (100 μ g./day); in hypophysectomized rats, activity of this enzyme was progressively reduced in the groups treated with growth hormone for 2, 5, and 10 days, only a fourth of the initial activity remaining in the last group. 4. In muscle, progressive reduction of Gl-Ox activity from the high level in hypophysectomized rats to a normal level, previously reported by Bartlett and Glynn (2), was confirmed. In liver, the changes in Gl-Ox activity were more complicated. 5. Incorporation of N 15 from labeled alanine into plasma fibrinogen; proteins of liver, spleen, kidney, and heart; and into collagen from Achilles tendon or tail, was only slightly greater in hypophysectomized rats treated with growth hormone than in untreated ones. Incorporation of N 15 into collagen was less than one-fifth as great as incorporation into fibrinogen. 6. Transfer of N 15 from labeled alanine to glutamic acid, tyrosine, and other amino acids occurred to the usual extent in hypophysectomized rats treated with growth hormone in doses (100 μ g./day) sufficient to produce nearly maximal gain in weight.