Interactions of prostaglandins with subpopulations of ovine luteal cells. II. Inhibitory effects of PGF2 alpha and protection by PGE2.

Purified preparations of ovine large luteal cells were utilized in a series of experiments to test the effects of prostaglandins (PG) E2 and F2 alpha on cell morphology, viability and secretion of progesterone. Luteal cells were allowed to attach to culture dishes overnight before experiments. In the first series of experiments incubation of large steroidogenic cells with PGF2 alpha for 6 hr resulted in morphological changes including a retraction of the cell cytoplasm and apparent extrusion of cytoplasmic components which became more pronounced after 12 hr. In a second series of experiments, PGF2 alpha decreased and PGE2 increased progesterone accumulation in media after 6 hr when media were not replaced during the incubation period, while progesterone accumulation was not different than that observed in control dishes when both prostaglandins were present. Hourly replacement of the media negated the inhibitory effects of PGF2 alpha but had no effect on the stimulated secretion of progesterone induced by PGE2. Finally, in incubations without media replacement, PGF2 alpha induced a dose-dependent decrease in progesterone accumulation while PGE2 elicited a biphasic response with progesterone secretion increasing from 0.1 ng/ml to maximal levels at 10 ng/ml followed by a dose-dependent decrease at 100 and 1000 ng/ml. These data are compatible with the hypotheses that: 1) luteolysis is initiated, at least in part, by an action of PGF2 alpha on large luteal cells; and 2) the embryonic signal from the pregnant uterus which rescues the ovine corpus luteum may be PGE2.