Distinct mechanisms regulate induction of messenger ribonucleic acid for prostaglandin (PG) G/H synthase-2, PGE (EP₃) receptor, and PGF(2α) receptor in bovine preovulatory follicles

We have evaluated the in vivo and in vitro regulation and temporal expression of messenger RNA (mRNA) for prostaglandin (PG) G/H synthase-2 (PGHS-2) and two specific PG receptors, PGF(2α) receptor (FP receptor) and PGE receptor EP₃ subtype (EP₃ receptor), in bovine preovulatory follicular cells and luteal cells. An in vivo study showed that PGHS-2 mRNA was not detected in granulosa cells and was highly but transiently induced by the LH surge before ovulation. FP and EP₃ receptor mRNAs were present at extremely low concentrations in granulosa or thecal cells and did not increase before ovulation. Messenger RNA for FP receptor increased more than 500- and 2500- fold at 24 and 48 h after ovulation, respectively, and these high amounts were maintained at midluteal phase. On the other hand, mRNA for EP₃ receptor remained low with FP receptor mRNA 1000-fold greater than EP₃ receptor mRNA in the corpus luteum. In vitro culture of bovine granulosa cells using hCG, forskolin, and phorbol didecanoate demonstrated that induction of FP receptor mRNA was mediated through protein kinase (PK) A. In contrast, EP₃ receptor mRNA was stimulated through PKC. PGHS-2 was acutely (<12 h) increased by PKA, and to a lesser extent by PKC. Temporal expression of FP receptor mRNA is not consistent with the involvement of FP receptor in ovulation and suggests that PKA stimulates PGHS-2 and FP receptor mRNA by distinct mechanisms.