[Zinc and the growth hormone system]

Chronic zinc nutritional deficiency constantly causes delay in pondero-statural growth. The mineral controls GH synthesis and secretion, but its administration acts on physical growth also after hypophysectomy: zinc supplementation causes a significant increase in liver synthesis of IGF-I (somatomedin C), which, in chronic mineral nutritional deficiency, is remarkably reduced. In men, in this condition, GH response to its releasing factor (GRF) is normal: a demonstration of the less important role of the pituitary gland in this situation. Therefore, in chronic zinc deficiency, reduced liver production of IGF-I is responsible for reduced physical growth; moreover in this situation receptor resistance to IGF-I (in addition to GH), that fades away after dietetic supplementation of the mineral, has been demonstrated. Therefore zinc play an important role at receptor level, throughout various mechanisms (including a proven increase in receptor number, due to its aggregating membrane direct induced effect).