Growth hormone-releasing factor regulates growth hormone mRNA in primary cultures of rat pituitary cells.

Abstract

A peptide with high intrinsic activity for specifically stimulating the secretion of immunoreactive growth hormone (GH; somatotropin) was characaterized and reproduced by total synthesis. This peptide, human pancreatic growth hormone-releasing factor, 44-amino-acid form (hpGRF1-44-NH2), was isolated from a tumor localized in the pancreas of a patient with acromegaly. The effect of this growth hormone-releasing factor (GRF) on GH release and the GH mRNA levels in monolayer cultures of rat pituitary is reported. The cytoplasmic dot hybridization technique was used to examine the effect of GRF on GH mRNA levels. Incubation of rat pituitary cultures with GRF for 72 h resulted in a 2- to 2.5-fold increase in GH mRNA levels, and the maximal levels of stimulation were achieved at GRF concentrations as low as 1 fM. GRF did not stimulate prolactin release, nor did it affect specific prolactin mRNA levels in the pituitary cultures. GRF is a potent and specific GH secretagogue that also affects specifically GH mRNA levels in normal pituitary cells.