Effects of Cortisol and Diethylstilbestrol on Growth Hormone Release by Rat Pituitary in vitro . ∗

Abstract

The secretion of growth hormone in response to hypoglycemia and the administration of arginine in man has been shown to be greatly influenced by certain non-pituitary hormones. Corticosteroids decrease growth hormone response to these stimuli in man (1,2) while estrogens and the synthetic estrogenic compound diethylstilbestrol facilitate the release of growth hormone(3,4). The mechanism of action of these modifying effects has not been established. Corticosteroids have little effect on the concentration of growth hormone in the pituitary of the normal rat(5). If corticosteroids are administered during the induction of hypoglycemia, the expected drop in growth hormone content is inhibited(5). Estrogens on the other hand decrease the concentration of growth hormone even when compared to pair fed control rats(6).

The modifying effects of estrogens and corticosteroids on growth hormone secretion could be exerted either at the level of the hypothalamus by affecting the secretion of the somatotropin releasing factor or these hormones could affect the secretion of growth hormone by acting directly on the somatotropic cells themselves. The observations of Pecile and Müeller (5) have suggested that cortisol may deplete the hypothalamus of somatotropin releasing factor. In their experiments hypothalamic extracts from cortisol treated animals had a much reduced capacity to cause a depletion of bioassayable pituitary growth hormone in recipient animals when compared to hypothalamic extracts from normal rats. Cortisol-treated recipient rats retained their ability to respond with a depletion of bioassayable growth hormone when injected with hypothalamic extracts from normal rats. Although one can not have complete confidence in the specificity of bioassay of crude pituitary extracts, these observations suggest that cortisol affects growth hormone release at the level of the hypothalamus.

Despite these observations we felt that it was important to study possible influences of corticosteroids and estrogens directly on the pituitary in the absence of hypothalamic tissue.