EFFECT OF LUTEINIZING-HORMONE (LH), PGE(2), 8-EPI-PGE(1), 8-EPI-PGE(2), TRICHOSANTHIN, AND PREGNANCY-SPECIFIC PROTEIN-B (PSPB) ON SECRETIONOF PROGESTERONE IN-VITRO BY CORPORA-LUTEA (CL) FROM NONPREGNANT AND PREGNANT COWS

Secretion of progesterone by Day 14 bovine corpora lutea (CL) of the e strous cycle and Day 200 CL of pregnancy was evaluated in vitro to det ermine what regulates secretion of progesterone by CL of pregnancy. We ights of Day 200 CL of pregnancy (4356 +/- 223g) were heavier when com pared to Day 14 CL of the estrous cycle of Brahman cows (3643 +/- 128 g; p less than or equal to 0.05); however, both Day 14 and Day 200 min ced CL slices secreted similar basal amounts of progesterone per unit mass (p greater than or equal to 0.05). Secretion of progesterone in v itro by Day 14 CL of the estrous cycle was increased at 4 and 8 h (p l ess than or equal to 0.05) by 10 or 100 ng/mL luteinizing hormone (LH) and did not differ between doses (p greater than or equal to 0.05). P rogesterone secretion in vitro by Day 200 CL of pregnancy was not incr eased (p greater than or equal to 0.05) by LH at 4 or 8 h. However, pr ogesterone secretion in vitro by Day 14 CL of the estrous cycle or Day 200 CL of pregnancy was increased (p less than or equal to 0.05) at 4 h by 10 or 100 ng/mL PGE, which did not differ by dose or reproductiv e status (p greater than or equal to 0.05). At 8 h, Day 14 CL of the e strous cycle secretion of progesterone in vitro was increased (p less than or equal to 0.05) by both doses of PGE, but only at 8 h by 100 ng /mL from Day 200 CL of pregnancy (p less than or equal to 0.05). Secre tion of progesterone in vitro was not affected (p greater than or equa l to 0.05) by 10 or 100 ng/mL 8-Epi-PGE(1) or 8-Epi-PGE(2) at 4 or 8 h from Day 14 CL of the estrous cycle or Day 200 of pregnancy. Trichosa nthin increased (p less than or equal to 0.05) secretion of progestero ne in vitro by 10 ng/mL at 4 h and at 8 h by Day 14 CL of the estrous cycle or at 8 h by Day 200 CL of pregnancy but trichosanthin at 100 ng /mL did not affect (p greater than or equal to 0.05) secretion of prog esterone in vitro by Day 14 CL of the estrous cycle or Day 200 CL of p regnancy at 4 or 8 h. Pregnancy specific protein B (PSPB) increased (p less than or equal to 0.05) secretion of progesterone in vitro at 4 a nd 8 h by Day 14 CL of the estrous cycle and did not differ between in cubation times (p greater than or equal to 0.05). PSPB increased secre tion of progesterone at 4 h but not at 8 h (p greater than or equal to 0.05) by Day 200 CL of pregnancy. These data suggest that PGE(2) or P SPB but not LH, 8-Epi-PGE(1) or 8-Epi-PGE(2) regulates luteal secretio n of progesterone by bovine CL at mid-pregnancy. In addition, it is su ggested that weights of bovine CL of pregnancy increase to compensate for a lack of placental secretion of progesterone.