Production of 6-keto-prostaglandin F1 alpha by rat granulosa cells in vitro.

The production of 6-keto-prostaglandin (PG)-F1 alpha by rat granulosa cells in vitro was measured in order to determine if the precursor of this compound, prostacyclin (PGI2), is a potential mediator of preovulatory changes in follicular function. Granulosa cells were collected from immature rats (27-29 days old) 48 h after an injection of PMSG (20 IU). The cells were incubated in medium 199 containing 1% BSA with or without arachidonic acid and various treatments for up to 5 h. PGI2 synthesis was determined by extracting the combined cells and medium, purifying the extract by thin layer chromatography, and measuring 6-keto-PGF1 alpha using a sensitive RIA. PGE synthesis was also determined by RIA in order to compare and contrast effects of treatments on PGE synthesis with those on 6-keto-PGF1 alpha synthesis. Both exogenous arachidonic acid and LH stimulated 6-keto-PGF1 alpha synthesis approximately 4-fold in comparison to controls during 5-h incubations. Maximum stimulation was achieved by the combination of arachidonic acid and LH. The effect of arachidonic acid was evident as early as 1 h of incubation, but LH had no effect until 3 h of incubation. PGE synthesis was also stimulated by arachidonic acid within 1 h of incubation and by LH within 3 h of incubation. A potent LHRH agonist also significantly stimulated 6-keto-PGF1 alpha and PGE production during a 5-h incubation, whereas three vasoactive agents (histamine, bradykinin, and angiotensin II) had no stimulatory effect on the synthesis of either compound. Based on the measurement of 6-keto-PGF1 alpha, it is concluded that rat granulosa cells have the capability to synthesize PGI2 and that this synthesis is stimulated by LH and a potent LHRH agonist. Therefore, PGI2 is a potential mediator of hormone actions in the preovulatory follicle.