Effects of indomethacin, luteinizing hormone (LH), prostaglandin E 2 (PGE 2), trilostane, mifepristone, ethamoxytriphetol (MER-25) on secretion of prostaglandin E (PGE), prostaglandin F 2α (PGF 2α) and progesterone by ovine corpora lutea of pregnancy or the estrous cycle

Abstract

Two experiments were conducted to determine the luteotropin of pregnancy in sheep and to examine autocrine and paracrine roles of progesterone and estradiol-17 β on progesterone secretion by the ovine corpus luteum (CL). Secretion of progesterone per unit mass by day-8 or day-11 CL of the estrous cycle was similar to day-90 CL of pregnancy ( P ≥ 0.05). In experiment 1, secretion of progesterone in vitro by slices of CL from ewes on day-8 of the estrous cycle was increased ( P ≤ 0.05) by LH or PGE 2. Secretion of progesterone in vitro by CL slices from day-90 pregnant ewes was not affected by LH ( P ≥ 0.05) while PGE 2 increased ( P ≤ 0.05) secretion of progesterone. Day 8 ovine CL of the estrous cycle did not secrete ( P ≥ 0.05) detectable quantities of PGF 2α or PGE while day-90 ovine CL of pregnancy secreted PGE ( P ≤ 0.05) but not PGF 2α. Secretion of progesterone and PGE in vitro by day-90 CL of pregnancy was decreased ( P ≤ 0.05) by indomethacin. The addition of PGE 2, but not LH, in combination with indomethacin overcame the decreases in progesterone by indomethacin ( P ≤ 0.05). In experiment 2, secretion of progesterone in vitro by day-11 CL of the estrous cycle was increased at 4-h ( P ≤ 0.05) in the absence of treatments. Both day-11 CL of the estrous cycle and day-90 CL of pregnancy secreted detectable quantities of PGE and PGF 2α ( P ≤ 0.05). In experiment 1, PGF 2α secretion by day-8 CL of the estrous cycle and day-90 ovine CL of pregnancy was undetectable, but was detectable in experiment 2 by day-90 CL. Day 90 ovine CL of pregnancy also secreted more PGE than day-11 CL of the estrous cycle ( P ≤ 0.05), whereas day-8 CL of the estrous cycle did not secrete detectable quantities of PGE ( P ≥ 0.05). Trilostane, mifepristone, or MER-25 did not affect secretion of progesterone, PGE, or PGF 2α by day-11 CL of the estrous cycle or day-90 CL of pregnancy ( P ≥ 0.05). It is concluded that PGE 2, not LH, is the luteotropin at day-90 of pregnancy in sheep and that progesterone does not modify the response to luteotropins. Thus, we found no evidence for an autocrine or paracrine role for progesterone or estradiol-17 36 on luteal secretion of progesterone, PGE or PGF 2α.