PGE 2 induces its own secretion in vitro by bovine 270-day placenta but not by 200-day placenta

Abstract

Two separate experiments were conducted to determine whether prostaglandin (PG) E 2 stimulates the secretion of progesterone by 270- or 200-day Brahman placentas in vitro. Secretion of progesterone, PGF 2α, pregnancy specific protein B, or estradiol-17β by 270-day Brahman placentas was not affected ( p ≥ 0.05) by PGE 2, during the 4-h incubation period at the doses tested. Indomethacin or meclofenamic acid decreased ( p ≤ 0.05) 270-day Brahman placental secretion of PGE and PGF 2α by 98 and 60%, respectively. However, PGE 2 induced ( p ≤ 0.05) its own secretion, but not the secretion of PGF 2α ( p ≥ 0.05), by 270-day Brahman placentas, even in the presence of indomethacin or meclofenamic acid at a dose of 100 ng/mL. Also, secretion of 8-Epi-PGE 2 by Day 270 Brahman placentas was increased ( p ≤ 0.05) by PGE 2. Secretion of progesterone, estradiol-17β, or pregnancy specific protein B by 200-day Brahman placentas was not affected by PGE 2, 8-Epi-PGE 2, PGF 2α, estradiol-17β, or trichosanthin during the 4- or 8-h incubation period ( p ≥ 0.05). Secretion of estradiol-17β at 8 h was lower ( p ≤ 0.05) in all treatment groups and did not differ ( p ≥ 0.05) among the 8-h incubation treatment groups. Secretion of PGE by 200-day Brahman placentas was reduced ( p < 0.05) by indomethacin 72 and 82% and by meclofenamic acid 72 and 96%, respectively, at 4 and 8 h when compared to controls. Secretion of PGF 2α was reduced ( p ≤ 0.05) 71 and 86% by indomethacin or 89 and 89% by meclofenamic acid at 4 and 8 h, respectively, and did not differ ( p ≥ 0.05) between 4 and 8 h of incubation. PGE 2 did not ( p ≥ 0.05) induce secretion of PGE above what was added in any treatment group. PGE in culture media was increased ( p ≤ 0.05) by 8-Epi-PGE 2, pregnancy specific protein B, and the 100 ng/mL PGF 2α dose ( p ≤ 0.05), but not by PGE 2, progesterone, estradiol-17β, 8-Epi-PGF 2α, or trichosanthin. Secretion of PGF 2α by 200-day Brahman placentas was not affected ( p ≥ 0.05) by 8-Epi-PGE 2, progesterone, or estradiol-17β, but PGF 2α secretion was increased ( p ≤ 0.05) by trichosanthin or PGE 2, even in the presence of indomethacin or meclofenamic acid. It is concluded that PGE does not affect secretion of progesterone by 200- or 270-day bovine placentas, but, pregnancy specific protein B may regulate placental secretion of PGE. Also, indomethacin and meclofenamic may affect enzymes converting PGH to PGE rather than acting only on cyclooxygenase because indomethacin and meclofenamic acid lowered PGE secretion by 270-day Brahman placentas more than they lowered PGF 2α. In addition, it is concluded that PGE 2 can induce bovine placental secretion of PGE, but this is dependent upon the stage of gestation.