Enhancement by Thyroxine of the Adrenal-Stimulating Effect of Somatotrophic Hormone

Abstract

Experiments on intact Sprague-Dawley rats indicate that the adrenal enlargement produced by somatotrophic hormone (STH) can be greatly augmented by simultaneous treatment with comparatively small doses of thyroxine. Within a certain dosage range, the corticotrophic effect of STH is even proportionate to the dose of thyroxine given. The adrenal enlargement produced by adrenocorticotrophic hormone (ACTH), on the other hand, is not enhanced by concurrent treatment with thyroxine.Attention is called to the fact that, in rats in which adrenocortical hypertrophy is produced, either by STH plus thyroxine or by ACTH plus thyroxine, many of the changes in the extraadrenal organs, which are generally considered to be indicative of increased glucocorticoid production (inhibition of body weight gain, splenic atrophy, involution of the thymus and lymph nodes, inhibition of inflammatory exudate formation), do not parallel the increase in adrenal weight.It is now well established that the ability of the pituitary to exert its corticotrophic action is largely dependent upon the thyroid. We were able to show, for instance, that the adrenal-enlarging effect of crude anterior pituitary extracts can be markedly enhanced by simultaneous treatment with thyroxine [Selye, Béland & Stone, 1945; Selye, Stone, Nielsen & Leblond, 1945]. On the other hand, thyroidectomy diminished the corticotrophic effect of similarly prepared hypophysial extracts [Hay, 1946 a, 6]. It would have been tempting to ascribe these phenomena to some synergism be¬ tween the thyroid and the ACTH contained in the pituitary extracts, but, at that time, we used a very crude bovine anterior lobe preparation which was apparently poor in corticotrophin, judging by the slight degree of adrenal enlargement it induced when given without thyroxine. On the other hand, our extract was especially rich in somatotrophic hormone (STH), as judged by its effect upon somatic growth, and its ability to produce nephrosclerosis and myocarditis in rats (after suitable 'conditioning' by unilateral nephrectomy and NaCl supplements). This raised the question as to whether thyroxine could enhance the corticotrophic effect of some pituitary principle other than ACTH, perhaps that of STH. From our observations and from a survey of the literature, it seems doubtful whether STH preparations, which contain no demonstrable ACTH contamination, can stimulate the growth of the adrenal cortex in hypophysectomized animals, although they do exert a corticotrophic effect in intact rats. However, when such purified preparations are administered in combination with threshold doses of ACTH,

Effect of Deficient Diets on Corticosteroid Synthesis by Rat Adrenals in Vitro and Its Relationship to Infections With Nippostrongylus Brasiliensis

“…It is difficult to account for this, since in general, when hypertrophy of the cortex occurs as in the present experiments, there is an increased corticosteroid output (Goodsell, 1941;Cohen, Freedman, Kleinberg, Schechter & Martin, 1954;Wendler Deane, 1962). However, it seems that somatotrophin (STH) alone or in combination with ACTH can affect the growth of the gland (Lostroh, 1958), and thyroxine and STH have been shown to increase adrenal weight without affecting that of the thymus or spleen (Bois & Selye, 1957), indicating that there was no increase in circulating corticosterone. Adrenal hypertrophy may occur therefore without concomitant increase in corticosteroid production.…”

Studies on Somatotropic Hormone Secretion in Gynecology and Obstetrics

“…(4) There is a common tendency in the changes of concentration between chorionic gonadotropin and placental STH-like substance and, in the last stage of pregnancy, between steroid hormones and STH-like substance in the plasma. (5) No STH-like hormone could be detected in the plasma of normal non gravidae, but it was found in a severe juvenile diabetic patient with retarded growth.…”