REGULATION OF BETA-ENDORPHIN SECRETION BY CORTICOTROPIN-RELEASING FACTOR IN THE INTACT RAT TESTIS

CRF stimulates beta-endorphin (beta-EP) secretion from adult rat Leydig cells in vitro. To evaluate the relevance of this action of CRF in a physiological context, we studied the effect of CRF on beta-EP secretion in the testis in whole animals. In the pubertal rat, intratesticular infusion of CRF resulted in a 3-fold stimulation of immunoreactive beta-EP (ir-beta-EP) levels in testicular interstitial fluid (TIF) compared with levels in contralateral saline-infused testes. Coadministration of the antagonist CRF-(12-41) resulted in TIF ir-beta-EP concentrations that were reduced compared to levels in paired saline controls. Infusion of the competitive antagonist CRF-(9-41) alone slightly stimulated ir-beta-EP concentrations in TIF. In adult animals, all of the peptides tested were without effect. These results suggest a developmental regulation of the action of CRF on beta-EP levels in the pubertal rat testis. Our studies in conjunction with documented results demonstrate that in the testis, beta-EP is actively secreted. These results imply that testicular ir-beta-EP is derived from a POMC mRNA that encodes a signal peptide containing preprohormone similar or identical to pituitary POMC. Previous studies of rodent testicular mRNA have found only 5'-truncated forms of POMC message. The current study provides direct evidence for a low abundance POMC transcript that could encode the preprohormone. Therefore, the major components of a pituitary-like CRF/POMC stimulus/secretion system appear to be present in the rat testis, including the full-length POMC mRNA and release of POMC-derived beta-EP that is stimulated by CRF.