FUNCTIONAL LUTEOLYSIS IN THE PSEUDOPREGNANT RAT: EFFECTS OF PROSTAGLANDIN F2α AND 16-ARYLOXY PROSTAGLANDIN F2α IN VITRO

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Abstract
The present work concerns the luteolytic effects of prostaglandin (PG) F2α and its analogue, 16-aryloxy PGF2α, upon isolated luteal cells. Varying doses of these two prostaglandins were incubated with cells in the presence or absence of an optimum stimulatory dose of LH (1 μg/ml). The total contents of progesterone and 20α-dihydroprogesterone in flasks were determined after the incubation periods by radioimmunoassay. Both prostaglandins inhibited basal synthesis of progesterone and 20α-dihydroprogesterone, maximum inhibition occurring at concentrations of either PG of between 250 and 500 ng/ml. In this dose range both prostaglandins were found to abolish LH-stimulated progestogen synthesis completely. These effects were discernible within 5 min of incubation. The studies demonstrated that the onset of PG-induced luteolysis in vitro is characterized by an inhibition of the biosynthesis of both progesterone and its weakly progestogenic metabolite, 20α-dihydroprogesterone; induction of 20α-hydroxysteroid dehydrogenase activity by either PG was not found in incubations extending up to 60 min. In contrast to their relative potencies in vivo, PGF2α and 16-aryloxy PGF2α were essentially equipotent in this in-vitro system.