PEPTIDES OF THE GROWTH HORMONE-RELEASING HORMONE FAMILY - DIFFERENTIAL EXPRESSION IN RAT TESTIS

Growth hormone-releasing hormone (GHRH) belongs to a family of peptide s expressed at high levels in the brain and digestive system of mammal s. We have identified GHRH mRNA and peptide in rat and human germ cell s, and detected a GHRH receptor mRNA in Sertoli cells. GHRH treatment of cultured Sertoli cells results in accumulation of cAMP and increase d expression of c-fos and stem cell factor (SCF), two facto rs critica l for normal germ cell development. The current study was designed to localize within testis the transcription of other members of the GHRH family, and their receptors, and to determine if they also stimulate S CF. RNAs from separated testicular cells were amplified by comparative reverse transcription-polymerase chain reaction (RT-PCR). Southern bl ot analysis of the PCR products verified the presence of five GHRH fam ily peptide and receptor transcripts in distinct testicular cell types . Transcripts encoding VIP and glucagon, and the receptors for pituita ry adenylate cyclase activating peptide (PACAP) and glucagon, were det ected predominantly in Leydig cells. In contrast, expression of GHRH, PACAP, secretin, and secretin receptor predominated in germ cells. Rec eptors for GHRH and VIP were expressed equally in all testicular cell types. To determine if, like GHRH, any of these other peptides activat e Sertoli cell expression of SCF, primary Sertoli cell cultures were t reated for 4-6 h with 10 or 100 nM of each individual factor. There wa s no consistent stimulation of SCF mRNA by VIP, PACAP, glucagon, or se cretin. Differential expression of these peptides and their receptors suggests that they may each have unique paracrine functions within the testis.