Interaction Between Growth Hormone and Cortisol on the Regulation of Liver Tyrosine Transaminase Activity

Abstract

1. Stress (30-min rough agitation upon a noisy laboratory shaker) decreased pituitary growth hormone content (tibia test) of the adult rat. 2. Shaker stress had no effect upon the corticoidsensitive enzyme tyrosine-α-ketoglu tar ate transaminase in the liver of the intact rat. This stress, however, increased the activity of a second corticoid- sensitive enzyme, tryptophan pyrrolase. The adrenalectomized rat similarly stressed exhibited a decreased transaminase activity with no change in tryptophan pyrrolase. This inhibitory effect was abolished by hypophysectomy. 3. Growth hormone, when administered just prior to cortisol, inhibited the enzyme inducing effects of the steroid upon transaminase. The induction of tryptophan pyrrolase, by cortisol, was not affected by growth hormone. 4. The opposing actions of growth hormone and adrenal corticoids on the activity of hepatic tyrosine transaminase may be representative of a category of adaptive responses which include 2 or more neuroendocrine mechanisms that interact at the tissue-cell level to regulate the activity of specific enzyme systems. (Endocrinology83: 475, 1968)