Insulin-like growth factor-I down-regulates ghrelin receptor (growth hormone secretagogue receptor) expression in the rat pituitary

The effects of insulin-like growth factor-I (IGF-I) on the ghrelin receptor [growth hormone secretagogue receptor (GHS-R)] gene expression and on the GH response to GHS in rat pituitary cell cultures were examined. Pituitary GHS-R mRNA levels were decreased in a dose (0.01-10 nM)- and time (4-12 h)-dependent manner by IGF-I as measured with reverse transcriptase (RT)-PCR. The basal GH secretion was not influenced by the pretreatment with IGF-I (1 nM for 8 h); however, the GH response to the receptor ligand, a synthetic GHS, KP-102 (100 nM, 15 min), was significantly reduced by pretreatment with IGF-I. Thus, the present studies indicate that IGF-I could inhibit GH secretion at least in part by regulating the expression of the GHS-R.