BETA-ENDORPHIN DIRECTLY INFLUENCES BOTH BASAL AND GNRH-INDUCED LH-RELEASE BY BOVINE PITUITARIES IN-VITRO

The aim of this study was to investigate the effects of beta-endorphin and naloxone on both basal and GnRH-induced LH release by static cell cultures and perfused bovine pituitaries collected from cows with P4 blood concentrations either > 5 ng/ml or < 1 ng/ml. Pituitaries were c ollected from cows and freed from pars nervosa. Anterior pituitary cel ls were dissociated with enzymes (collagenase, hyaluronidase and DNAse ) and cultured for 48 h. Subsequently, the cells were exposed to beta- endorphin (0.1-10 nM) or naloxone (0.1 nM to 1 mu M) for 3 h and then treated with GnRH (10 nM) for an additional 3-h period. For perfusion, small pieces of anterior pituitary were placed into chambers and expo sed to beta-endorphin (1 nM) or naloxone (1 mu M) for 300 min, GnRH (1 nM) was infused twice as a 5 min pulse at + 150 and + 300 min after t he onset of perfusion. A competitive enzyme-linked immunosorbent assay (ELISA) was used to determine the LH content in cultured media and in perfusion samples. In cell cultures beta-endorphin (10 nM) reduced (p < 0.05) basal LH release by 18% and, at the concentrations of 1 and 1 0 nM, lowered GnRH-induced LH release (by 24 and 21%, respectively); n aloxone did not affect basal and GnRH-induced LH release. In perfused pituitaries beta-endorphin inhibited (p < 0.05) both basal and GnRH-in duced LH release in both groups; naloxone did not exert any significan t effect. The data from this study demonstrate that beta-endorphin mod ulates LH release by acting directly at the pituitary level.