[Growth hormone-releasing peptides (GHRP) and their analogues]

The synthetic growth hormone-releasing peptides (GHRPs) and their nonpeptide analogues release growth hormone (GH). They are not only effective parenterally, but also intranasally and if given in the appropriate doses, they are active orally as well. The exact mechanism of action has not been fully established. There is probably a dual site of action. According to experiments on in vitro pituitary membranes, they directly stimulate GH secreting cells, but they are also active in the hypothalamus. This latter site of effect seems to be the more important in vivo. The presence of the endogenous growth hormone-releasing hormone (GHRH) is needed for their full action in humans. Their hypothalamic action involves either direct stimulation of GHRH neurons, or/and they act as functional somatostatin antagonists or possibly they act via an unknown hypothalamic factor. Intravenous administration causes marked GH release in humans and GHRPs synergise with GHRH in causing high GH output. They release GH in short stature children and in growth hormone deficient adults and in other situations of GH deficiency, such as obesity, catabolic diseases and old age. The role of GHRPs in the diagnosis and treatment of GH deficient states requires further wide-spread investigations.