The inducible form of prostaglandin endoperoxide-2 (PGS-2) is transiently induced by activators of the protein kinase A and protein kinase C systems in rat preovulatory (PO) granulosa cells. This induction is suggested to play an important role in the ovulatory process, which shares many of the characteristics of an inflammatory reaction. The purpose of the present study was to explore the role of progesterone (P4) as an 'anti- inflammatory' steroid for the regulation of PGS-2 and the synthesis of prostaglandins in the PO follicle. Isolated rat PO follicles were preincubated with different amounts of exogenous P4before the addition of luteinizing hormone (LH) and 3-isobutyl-1-methylxanthine (IBMX) (LH+I). Medium levels of prostaglandin E2(PGE2) were measured by RIA and the protein contents of PGS-1 and PGS-2 were determined by immunoblotting. LH+I. Both the content of PGS-2 and the synthesis of PGE2were decreased. The content of PGS-1 demonstrated only minor changes in response to P4. These results showed a dual regulation of PGS-2 in the rat PO follicle with both stimulatory and inhibitory pathways. One of the 'anti-inflammatory' actions exerted by P4in the present study was to reduce the expression of PGS-2 and the follicular production of prostaglandins. This action might be of importance for restriction and control of the inflammatory response in the ovulatory process in vivo.
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