Placental lactogen as a regulator of luteal cells function during pregnancy in sheep

The luteotropic activity of ovine placental lactogen (oPL) on different day s of gestation in ewes was assessed using in vitro methods. Corpora lutea ( CL) harvested on Days 45, 70, 95, 120 and 135 of gestation and during partu rition were enzymatically dispersed and plated on multiwell plates. After 4 8 h of incubation, all cultures were terminated and media were frozen for f urther steroid analysis. Cells were cultured in control medium, with additi on of oPL alone, or in combination with PGE(2) or PGF(2 alpha). Supplementation of culture media with oPL increased basal progesterone secr etion by cells isolated on Days 45 and 70 of gestation. There was no effect on progesterone secretion by cells isolated on other days of gestation; PG E(2) added to the culture media increased progesterone production only by c ells isolated on Day 70 of regnancy. Simultaneous oPL treatment with PGE2 h ad a statistically significant and stimulatory effect on progesterone produ ction by luteal cells collected on Day 70 and 95 of regnancy. In contrast, PGF(2 alpha), alone in culture media decreased progesterone secretion by ce lls isolated on Days 45, 70 and 95 of gestation, while oPL plus PGF(2 alpha ) on Days 70 and 95 of gestation protected against luteolytic action of PGF (2 alpha). The results showed 1) a direct effect of the oPL on luteal cells isolated o n Days 45 and 70 of gestation; 2) synergism between PL and PGE2 in progeste rone production; by cells isolated on Day 70; 3) and a luteoprotective effe ct of oPL against the luteolytic action of prostaglandin F (PGF(2 alpha)) o bserved on Days 70 and 95 of gestation. (C) 2000 by Elsevier Science Inc.