Growth hormone has no direct effect on human adrenal steroid and insulin-like growth factor-binding protein secretion

Although it is known that growth hormone (GH) exerts its growth-promoting e ffects mainly via Insulin-like growth factor-I (IGF-I), an increasing numbe r of direct effects of GH has been described in many tissues. In vivo, mice transgenic for human growth hormone (hGH) show significantly elevated leve ls of corticosterone, enlarged adrenal glands, and altered levels of insuli n-like growth factor binding proteins (IGF-BPs). Recently, we have shown th at IGF's induce the secretion of cortisol and IGF-BP's in adult human adren ocortical cells. However, since human adrenal glands express the intact GH- receptor, the objective of this study was to investigate whether GH exerts a direct effect on the steroidogenesis and IGF-BP synthesis in adult human adrenocortical cells. Primary cell cultures in monolayer were incubated und er serum-free conditions with human growth hormone and/or ACTH for up to 72 hours. Cortisol was measured by specific RIA and the secretion of insulin- like growth factor binding proteins was analyzed by Western ligand blotting . hGH alone was unable to stimulate basal or ACTH-induced cortisol secretio n. Additionally, neither hGH alone or in combination with ACTH did signific antly alter the secretion of IGF-BP's. Therefore we conclude that hGH is un able to directly stimulate cortisol secretion and IGF-BP secretion in cultu red human adrenocortical cells.