Hormonal Control of Pancreatic Islet Functions

Abstract

A hormonal control of the pancreatic islets has been suspected for many decades, and a number of mechanisms have been implicated. In particular, the association of diabetes mellitus with pituitary- and adrenal-related aberrations (acromegaly, Cushing’s syndrome), the alleviation of diabetic symptoms by removal of pituitary and adrenal glands, and the induction of diabetic symptoms or islet alterations by injections of pituitary and adrenal hormones, raises the question of specific insulotropic hormonal effects (see e. g., Bratusch-Marrain 1983; Ganda and Soeldner 1983; Pek and Spangler 1983; Schade and Eaton 1983; Volk and Wellmann 1985e). However, no specific adenohypophysial or pituitary-dependent insulotropic hormones have been identified with certainty. Rather, the effects of these hormones (with the possible exception of the ovarian and thyroid secretions) seem to have been due to indirect, mainly metabolic, interactions. On the other hand, direct insulotropic effects of adrenomedullary hormones have been identified, and new insulotropic candidates have been ascribed to two additional endocrine systems: (1) hypothalamus; (2) gastrointestinal mucosa. The hypothalamic insulotropic secretions require further studies; the gastrointestinal “incretins” are poorly characterized even in mammals. Since we discussed the hypothalamic insulotropic factors in Chap. 7, we will deal in the following only with the adrenomedullary secretions and the incretins.