Effects of Luteinizing Hormone (LH), PGE 2, 8-Epi-PGE 1, 8-Epi-PGF 2α, Trichosanthin and Pregnancy Specific Protein B (PSPB) on Secretion of Prostaglandin (PG) E (PGE) or F 2α (PGF 2α) In Vitro by Corpora Lutea (CL) From Nonpregnant and Pregnant Cows

Abstract

Both Day 14 corpora lutea (CL) of the estrous cycle and Day 200 CL of pregnancy secrete detectable prostaglandin E (PGE) and prostaglandin F 2α (PGF 2α) in vitro. Corpora lutea from Day 200 pregnant cows secrete more PGE and PGFα in vitro than Day 14 CL of the estrous cycle when incubated in control medium without treatments ( p ≤ 0.05). In addition, secretion of both PGE and PGF 2α in vitro by both Day 200 CL of pregnancy and Day 14 of the estrous cycle increase ( p ≤ 0.05) with time in culture in the absence of treatments. The PGE: PGF 2α 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 ≥ 0.05), while the PGE: PGF 2α 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 ≤ 0.05) to 0.4. The PGE: PGF 2α ratio at 8 h by 200 day CL of pregnancy was lower ( p ≤ 0.05) than in the Day 14 CL of the estrous cycle at 4 or 8 h. Secretion of PGE or PGF 2α 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 ≤ 0.05). In summary, the altered ratio of PGE: PGF 2α 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.