Effect of insulin-like growth factor-I on growth hormone-releasing factor receptor expression in primary rat anterior pituitary cell culture

We examined the effect of insulin-like growth factor-I (IGF-I) on GH-releas ing factor (GRF) receptor expression in the primary rat anterior pituitary cell culture. The levels of GRF receptor mRNA were dose-dependently reduced by IGF-I treatment for 24 h. To clarify whether altered levels of GRF rece ptor mRNA contribute to GRF receptor concentrations, we examined the GH res ponse to GRF in vitro. There was no difference in basal GH secretion betwee n control and IGF-I pretreated cells, while GRF-stimulated GH secretion in cells pretreated with IGF-I for 24 h was significantly lower than that in c ontrol cells. Moreover, specific [I-125] Tyr(10)-human GRF binding to pitui tary cells was reduced significantly by IGF-I treatment. These results sugg est that IGF-I acts directly on the pituitary a nd participates in the regu lation of GRF receptor expression. (C) 1999 Elsevier Science Ireland Ltd. A ll rights reserved.