Effect of exogenous ovine placental lactogen on basal and prostaglandin-stimulated progesterone production by porcine luteal cells

The ability of ovine placental lactogen (oPL) to stimulate progesterone sec retion of porcine luteal cells isolated from ovaries in different stages of the oestrous cycle and to support the luteotropic action of PGE(2) or to p rotect the corpus luteum (CL) against the luteolytic action of PGF(2 alpha) was investigated. oPL in all doses used had no effect on progesterone prod uction of cells isolated from early developing corpora lutea while in doses of 1 and 10 ng/ml it increased oestradiol secretion by this type of cells. In doses of 1, 10 and 100 ng/ml it also increased progesterone secretion o f cells isolated from mature corpora lutea in a dose-dependent manner. No i nfluence on progesterone production of cells isolated from regressing corpo ra lutea was observed. oPL added to the culture media had no effect on PGE( 2)-stimulated progesterone production by cells isolated from mature corpora lutea. However, it exerted a protective effect against the luteolytic acti on of PGF(2 alpha) observed in cultures treated with PGF(2 alpha) alone or in combination with PGE(2) in a ratio of 4:1. These studies provide evidenc e that oPL is luteotropic and supports progesterone production in swine. Th e fact that oPL acted directly on ovarian steroidogenesis suggests that it may also play some role under non-pregnant physiological conditions. Future studies of structural and functional proteins secreted by the porcine conc eptus will help resolve this uncertainty.