Studies on growth hormone. IV. The effects of changing amino acid concentrations upon the hormonal regulation of protein metabolism in the isolated, perfused liver.

Abstract

Abstract The effects of GH and insulin upon the metabolism of perfused rabbit liver are altered considerably by changes in the perfusate amino acid levels. Thus, with physiologic levels of amino acids and in contrast to the "high-level" experiments: 1.1. GH no longer decreases urea production, but actually increases it. 2.2. Insulin decreases urea production. 3.3. GH produces a rising amino acid level, and insulin produces a falling amino acid concentration. These effects are directionally in agreement with the high-level results; however, the low-level GH curve ascends to a plateau while the high-level GH curve descends to its plateau. 4.4. Both GH and insulin-induced C 14 perfusate protein activity were much closer to control levels than in the presence of high alpha amino nitrogen concentrations. 5.5. The directional effects of both hormones on perfusate glucose concentrations were independent of amino acid concentration, insulin causing hyperglycemia and GH hypoglycemia. These effects on the isolated liver are directly opposite to those seen following the administration of these hormones to intact animals. 6.6. The results indicate that GH increases amino acid and protein turnover rates with low-substrate levels, while decreasing them with high levels. In contrast, insulin acts to slow amino acid and protein turnover at low alpha amino acid levels, and speed it (relative to both GH and controls) at high levels. Various facets of this interesting relationship are discussed.