Effects of luteinizing hormone (LH), PGE2, 8-Epi-PGE1, 8-Epi-PGF2α, trichosanthin and pregnancy specific protein B (PSPB) on secretion of prostaglandin (PG)E (PGE) or F2α (PGF2α) 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 cows secrete more PGE and PGF alpha in vitro than Day 14 CL of the estrous 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)alpha in vitro by both Day 200 CL of pregnancy and Day 24 of the estrous cycle increase (p less than or equal to 0.05) with time in culture in 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 pregnancy 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 affected by luteinizing hormone, PGE(2),. 8-Epi-PGE(1), 8-Epi-PGE(2), trichosanthin, 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 progesterone at 8 h by Day 200 CL of pregnancy reported previously from the same samples. In addition, caution should be exercised in interpretation of progesterone secretion data with bovine CL studies in vitro. Also, PSPB may play an indirect role through PGE to regulate bovine luteal secretion of progesterone.