EFFECTS OF LUTEINIZING-HORMONE (LH), PGE(2), 8-EPI-PGE(1), 8-EPI-PGF(2-ALPHA), TRICHOSANTHIN AND PREGNANCY-SPECIFIC PROTEIN-B (PSPB) ON SECRETION OF PROSTAGLANDIN (PG)E (PGE) OR F2-ALPHA (PGF(2-ALPHA)) IN-VITRO BY CORPORA-LUTEA (CL) FROM NONPREGNANT AND PREGNANT COWS

Both Day 14 corpora lutea (CL) of the estrous cycle and Day 200 CL of pregnancy secrete detectable prostaglandin E (PGE) and prostaglandin F (2)alpha (PGF(2)alpha) in vitro. Corpora lutea from Day 200 pregnant c ows secrete more PGE and PGF alpha in vitro than Day 14 CL of the estr ous cycle when incubated in control medium without treatments (p less than or equal to 0.05). In addition, secretion of both PGE and PGF(2)a lpha in vitro by both Day 200 CL of pregnancy and Day 24 of the estrou s cycle increase (p less than or equal to 0.05) with time in culture i n the absence of treatments. The PGE: PGF(2)alpha ratio secreted at 4 h in the absence of treatments by Day 14 CL of the estrous cycle was 1 .2 and at 8 h was 1.0 and did not differ (p greater than or equal to 0 .05), while the PGE: PGF(2)alpha ratio secreted by 200 day CL of pregn ancy in the absence of treatments at 4 h was 0.8 and at 8 h decreased (p less than or equal to 0.05) to 0.4. The PGE: PGF(2)alpha ratio at 8 h by 200 day CL of pregnancy was lower (p I 0.05) than in the Day 24 CL of the es cycle at 4 or 8 h. Secretion of PGE or PGF(2)alpha was af fected by luteinizing hormone, PGE(2),. 8-Epi-PGE(1), 8-Epi-PGE(2), tr ichosanthin, and pregnancy specific protein B (PSPB) and was time and dose dependent (p less than or equal to 0.05). In summary, the altered ratio of PGE: PGF(2)alpha may explain the decreased secretion of prog esterone at 8 h by Day 200 CL of pregnancy reported previously from th e same samples. In addition, caution should be exercised in interpreta tion of progesterone secretion data with bovine CL studies in vitro. A lso, PSPB may play an indirect role through PGE to regulate bovine lut eal secretion of progesterone.