Large luteal cells are the source of immunoreactive beta-endorphin in the pig: effects of HCG and TNFA on its secretion by luteal cells in vitro.

OBJECTIVE 1. To compare the release of beta-endorphin-like immunoreactivity (beta-END-LI) by large and small luteal cells of the pig; 2. to test the effects of human chorionic gonadotropin (hCG) either alone or combined with the cytokine TNFalpha on beta-END-LI secretion by these cells. METHODS Isolated large and small luteal cells on days 8-10 of the cycle (n=7) were incubated in M199 supplemented with hydrocortisone (40 ng/ml), transferrin (5 microg/ml), insulin (2 microg/ml), gentamicin (50 microg/ml), nystatin (240 U/ml), porcine low-density lipoproteins (LDL; 100 microg/ml), 1 % BSA and 2 x 10(-5) M bacitracin, for 12 h at 37 C and under the atmosphere of 95 % air and 5 % CO2. The cells were treated either with hCG (100 ng/ml) or TNFalpha (0.1, 1 and 3 nM) alone or with both agents together. Beta-END-LI concentration in incubation media was measured by RIA. RESULTS beta-END-LI secretion by large luteal cells was 15-fold greater than by small cells (666.38 +/- 24.59 pg/ml/106 cells vs. 44.60 +/- 2.53 pg/ml/106 cells). hCG enhanced beta-END-LI secretion by both large and small luteal cells. TNFalpha alone had no effect on beta-END-LI release by large and small luteal cells, but it abolished the stimulatory effect of hCG on beta-END-LI secretion by large luteal cells. CONCLUSION The results indicate that large luteal cells are a major source of beta-endorphin in the porcine corpus luteum, where its release may be affected by gonadotropins (possibly LH) and TNFalpha.