Growth hormone and growth hormone releasing hormone

摘要

Growth hormone (GH) is secreted by the anterior pituitary in a pulsatile fashion. Its secretion is tightly regulated by hypothalamic factors and by feedback from peripheral factors such as serum glucose and fatty acid levels. The hypothalamic input includes the reciprocal secretion of somatostatin and growth hormone releasing hormone (GHRH). Thus, a pulse of GH is mediated by suppression of tonic hypothalamic somatostatin secretion associated with an increase in GHRH secretion. This will not be further discussed but has been reviewed in detail previously (Tannenbaum & Ling, 1984; Thorner et al ., 1986). As shown in Figure 1, GH is also regulated by circulating levels of somatomedin C (otherwise known as insulinlike growth factor) which is either produced locally or in the periphery. Thus, somatomedin C inhibits GH secretion at both the pituitary and hypothalamic levels by modulating somatostatin and possibly also GHRH secretion. Another important influence on GH secretion is gonadal steroids. This occurs in both the human and in animals.