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.