Dependence on prolactin of the luteolytic effect of prostaglandin F-2 alpha in rat luteal cell cultures

Luteal regression is a multistep, prolonged process, and longterm luteal cu ltures are required for studying it in vitro. Cell suspensions from ovaries of superovulated rats were enriched with steroidogenic cells, seeded on la minin or fibronectin and maintained in defined medium for up to 10 days. Pr ogesterone secretion was much lower than that of 20 alpha -dihydroprogester one, a product of 20 alpha -hydroxysteroid dehydrogenase (20 alpha -HSD). P rolactin added throughout the incubation period gradually increased the per cent progesterone out of total progestins to fourfold, while reducing 20 al pha -HSD mRNA by 73%. Luteinizing hormone accelerated the establishment of higher percent progesterone by prolactin but by itself had no effect. Prola ctin did not increase total progestin production or cytochrome P450 side-ch ain cleavage (P450(scc)) mRNA. Cell viability was unaffected by prolactin a nd/or LH. Prostaglandin F-2 alpha (PGF(2 alpha)) was added 7-8 days after s eeding. in prolactin-treated cells, PGF(2 alpha) reduced steroidogenesis af ter 4-45 h, and at 45 h total progestins and P450(scc) mRNA were reduced by 45%. At 8-45 h PGF(2 alpha) reduced the percent progesterone out of total progestins, and at 45 h 20 alpha -HSD mRNA was doubled. In contrast, in pro lactin-deprived cultures, PGF(2 alpha) had little effect on total progestin s or 20(alpha)-HSD mRNA but doubled P450(scc). mRNA. Phospholipase C activi ty was stimulated by PGF(2 alpha). regardless of prolactin. Thus, when prol actin-treated, our cultures are a good model for mature corpora lutea chall enged with PGF(2 alpha); the finding that without prolactin PGF(2 alpha) ha s an alternative set of actions could help in identifying the signaling pat hways of PGF(2 alpha) responsible for its luteolytic effects.