PROSTAGLANDIN G H SYNTHASE-2 IS EXPRESSED IN BOVINE PREOVULATORY FOLLICLES AFTER THE ENDOGENOUS SURGE OF LUTEINIZING-HORMONE/

To determine whether prostaglandin G/H synthase-2 (PGHS-2) induction o ccurs under physiological conditions, heifers were ovariectomized and preovulatory follicles were isolated 0 (n = 4), 18 (n = 4), and 24 h ( n = 4) after the onset of estrus. The time of the LH surge was determi ned in blood samples collected every 4 h pre- and postestrus. Preparat ions of follicle wall and isolated theca interna and granulosa cells w ere analyzed for PGHS-2 protein and mRNA by immunoblot and Northern bl ot, respectively. Immunohistochemistry was used to document the in sit u localization of PGHS-2 protein, and follicular fluid concentrations of prostaglandin (PG) E-2 and PGF(2 alpha) were determined to monitor changes in PG synthetic activities. Results showed that PGHS-2 mRNA (4 .0 kilobases) and protein (74 000 M-r) were absent in preovulatory fol licles isolated at the onset of estrus, low in follicles obtained 18 h after estrus (16.0 +/- 1.2 h post-LH surge), and markedly induced 24 h postestrus (20 +/- 0 h post-LH surge). Immunoblot and immunohistoche mical analyses revealed that PGHS-2 protein was selectively induced in granulosa cells. Follicular fluid concentrations of PGE(2) and PGF(2 alpha) increased significantly (p < 0.01) between 0 and 24 h after est rus (from 2.8 +/- 0.2 to 87.9 +/- 30.9 ng/ml for PGE(2); from 0.05 +/- 0.02 to 68.9 +/- 23.6 ng/ml for PGF(2 alpha)). Collectively, these re sults clearly demonstrate that the induction of PGHS-2 in bovine preov ulatory follicles is a physiological event that occurs after the endog enous LH surge.