Inhibition of growth hormone and thyrotropin release by growth hormone-release inhibiting hormone

Abstract

Addition of increasing doses of synthetic growth hormone-release inhibiting hormone (GH-RIH) leads to a progressive decrease of the basal and N 6monobutyryl cyclic AMP-,theophylline- and prostaglandin E 2-induced release of immunoreactive growth hormone (GH) and thyrotropin (TSH) release from rat anterior pituitary cells in monolayer culture. A halfmaximal effect is measured at 3 × 10 −9 M GH-RIH while a maximal inhibition to 10–20% of the control level is found at 1 × 10 −7 M. Using rat hemipituitaries and measurement of GH release by both polyacrylamide gel electrophoresis and radioimmunoassay, a maximal effect of GH-RIH was found in the first 5 min of incubation. The inhibitory effect of GH-RIH on GH release remained constant for at least 3 h. GH-RIH does not affect the basal or induced release of prolactin and luteinizing hormone nor the high K +-induced release of GH and TSH.