DIFFERENTIAL GENE-EXPRESSION OF GROWTH-HORMONE (GH)-RELEASING HORMONE(GRH) AND GRH RECEPTOR IN VARIOUS RAT-TISSUES

Growth hormone (GH)-releasing hormone (GRH) acts on specific receptors in the anterior pituitary to stimulate the synthesis and release of G H. Recent reports suggest that GRH is also synthesized in extrahypotha lamic tissues. To evaluate the potential roles of extrahypothalamic GR H, we studied the gene expression of GRH and GRH receptors in various rat tissues by reverse transcribed (RT)-polymerase chain reaction(PCR) . Total RNA was extracted from twenty-three rat organs and RT-PCR was performed with GRH and GRH receptor primers. Highly-sensitive RT-PCR-S outhern blotting showed that GRH and GRH receptor mRNA coexist in the widespread tissues (14 of 25 tissues). GRH mRNA was relatively abundan t in the cerebral cortex, brain stem, testis, and placenta, while GRH receptor mRNA was abundant in renal medulla and renal pelvis. Northern blot hybridization using poly A+ RNA indicated that the transcript of GRH receptor gene found in the renal medulla was similar to the longe r transcript (about 4 Kb) of pituitary GRH receptor in the size. These results suggest that GRH plays a potential role not only in the neuro endocrine axis, but also in the autocrine and paracrine systems in ext rahypothalamic tissues.