IDENTIFICATION AND LOCALIZATION OF SECRETIN AND SECRETIN RECEPTOR MESSENGER-RNAS IN RAT TESTIS

Secretin is a well-conserved member of the growth hormone-releasing ho rmone (GHRH) family of peptides expressed in brain, gut and gonads. To determine whether secretin may also play a physiological role in test is, we examined the level and cellular distribution of secretin and se cretin receptor gene expression in rat testis. RNAs from total testis, Sertoli, germ and Leydig cells were amplified by comparative reverse transcription-polymerase chain reaction (RT-PCR). Southern blot analys is of the PCR products indicated secretin and secretin receptor mRNA e xpression primarily in germ cells. Sequence comparisons of cloned secr etin and secretin receptor PCR products showed 100% identity with the previously reported sequences. To localize secretin and secretin recep tor mRNAs at the cellular level within testis, in situ hybridization w as performed. Specific hybridization to secretin mRNA was observed in low abundance in many germ cell types, but was heaviest over step 19 s permatids in stages VII and VIII tubules. Secretin receptor mRNA was d etected in approximately the same cell types as was secretin mRNA, exc ept that labeling was greatest in round spermatids (steps 6-8). Since the patterns of gene expression of secretin and its receptor overlap, these data suggest that there may be an intrinsic secretin system in t estis.