Hypothalamic growth hormone-releasing factor (GRF) regulates its own receptor gene expression in vivo in the rat pituitary.

peptide that specifically stimulates both synthesis and secretion of pituitary GH [1]. GRF is released into the hypophyseal-portal vessels under control by a variety of neurotransmitters and neuropeptides. After reaching the pituitary, GRF binds to its specific receptors [1] on somatotrophs and generates bursts of GH secretion episodically [2]. Earlier ligand-binding and functional studies in rats have shown that GRF down-regulates its own receptors in the pituitary [3, 4], but the mechanisms of down-regulation remain to be fully determined. We investigated how GRF regulated its own receptors at the gene expression level and report here evidence indicating that GRF receptor mRNA levels are upor down-regulated in vivo in the absence or presence of GRF, respectively.