Acute effects of prostaglandin F_2α on inositol phospholipid hydrolysis in the large and small cells of the bovine corpus luteum

The present studies were conducted to determine whether the large or small bovine luteal cell was the site for the stimulatory effect of prostaglandin F_2α (PGF) on phospholipase C-catalyzed inositol phospholipid hydrolysis. Corpora lutea were removed from heifers during the luteal phase of the normal estrous cycle. Small luteal cells were isolated by unit-gravity sedimentation and large luteal cells were isolated by flow cytometry using a Becton Dickinson FACS 440 cell sorter. PGF provoked rapid (5-30 s) and sustained (up to 30 min) increases in the levels of inositol mono-, bis-, and trisphosphates (IP, IP₂, IP₃, respectively) in small luteal cells. IP₃ was formed more rapidly than IP₂ or IP following PGF treatment. The PGF-stimulated increase in IP₃ was accompanied by a transient reduction in the levels of ³H-labeled phosphatidylinositol 4,5-bisphosphate. LiCl (10 mM) enhanced inositol phosphate accumulation in response to PGF. Maximal increases in inositol phosphate accumulation were observed with 1-10 μM PGF and half-maximal increases were observed with 60 nM PGF. PGF (1-10 μM) had no effect on cAMP levels but stimulated small increases in progesterone accumulation in 30 min incubations of small luteal cells. PGF also increased the accumulation of inositol phosphates in large luteal cells. The increases were apparent within 5 min of incubation (the earliest time examined) and further increases were observed in incubations lasting 30 min. PGF had no significant effect on cAMP or progesterone in 30 min incubations of large cells. These findings demonstrate that PGF stimulates phospholipase C activity in both large and small bovine luteal cells and provide further evidence for the involvement of calcium and protein kinase C in the action of PGF.