Amine Synthesis in Regenerating Rat Liver: Effect of Hypophysectomy and Growth Hormone on Ornithine Decarboxlyase

Abstract

The effect of hypophysectomy and subsequent hormone therapy on ornithine decarboxylase (ORD) activity was examined in regenerating rat liver. Enzyme activity was determined by measuring the liberation of 14CO2 from carboxyl-labeled ornithine. In rats with intact pituitaries, ORD activity 4 hr after hepatectomy was 10 times that of sham-operated controls. Hypophysectomized rats failed to show an increase in ORD activity 4 hr after hepatectomy. A time course study showed that hypophysectomy resulted in a delayed increase and an early decline of ORD activity after partial hepatectomy. After the removal of thyroids, adrenals, ovaries, or testes, the increase in ORD activity 4 hr after hepatectomy was the same as in control animals. Treating hypophysectomized animals with triiodothyronine piior to hepatectomy produced a small but significant increase in enzyme activity. Growth hormone treatment produced a greater enhancement, although enzyme levels were still lower than those of control rats. Combined treatment of hypophysectomized rats with growth hormone and triiodothyronine restored ORD activity 4 hr after hepatectomy to levels of control rats. Growth hormone administration to normal rats for 3 days produced a 3-fold enhancement of liver ORD activity. (Endocrinology 84: 223, 1969)