Effect of exogenous ovine placental lactogen on luteolysis induced by prostaglandin F-2 alpha in sheep.

The ability of ovine placental lactogen (oPL) to stimulate progesterone secretion by the ovary as well as its ability to protect the corpus luteum against the luteolytic action of PGF-2 alpha was investigated. When oPL was infused alone into the ovary for 2 h on Day 12 of an induced cycle at rates of 0.6, 6.0, 30.0 or 60.0 micrograms/h there was no significant increase in progesterone secretion by the autotransplanted ovary in 7 sheep. An extension of the infusion of oPL did not prevent luteal regression during the administration of PGF-2 alpha given either continuously (10 micrograms/h for 6 h, 5 sheep) or as 5 pulses each lasting 1 h and of increasing concentration in 25 h (2 sheep). We conclude that oPL does not (a) stimulate progesterone secretion when infused directly into the arterial supply of the ovary or (b) have any direct protective effect against the luteolytic action of PGF-2 alpha on the ovine CL.