Growth Hormone Secretagogue Receptors Discovered in Diverse Human Peripheral Tissues

Growth hormone secretagogues (GHS) are synthetic compounds known to stimulate the release of growth hormone (GH) from the pituitary gland. While their central actions were well-established, the extent of their direct effects on other organs remained less clear. This study aimed to identify and characterize GHS binding sites in various human peripheral tissues, providing insights into potential GH-independent actions.

The study confirmed high-density GHS binding sites in the pituitary gland, as expected, but also revealed significant novel findings in peripheral organs. High-affinity, saturable GHS binding was prominently detected in the adrenal cortex, thyroid gland, and pancreatic islets, with binding densities comparable to or exceeding some known endocrine tissues. For instance, the adrenal cortex showed a 2.8-fold higher binding density compared to the liver, and pancreatic islets exhibited 3.5-fold greater specific binding than exocrine pancreas. Moderate binding was observed in myocardial tissue and renal cortex, while negligible binding was found in lung, skeletal muscle, and spleen. The dissociation constant (Kd) for [125I]GHRP-6 in these novel sites ranged from 0.7 nM to 1.2 nM, indicating high-affinity interactions. The study identified novel, high-affinity growth hormone secretagogue (GHS) binding sites in the human adrenal cortex, thyroid gland, and pancreatic islets, suggesting direct peripheral actions beyond the pituitary.