Prostaglandin G/H synthase-2 is expressed in bovine preovulatory follicles after the endogenous surge of luteinizing hormone

Abstract

To determine whether prostaglandin G/H synthase-2 (PGHS-2) induction occurs 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 determined in blood samples collected every 4 h pre- and postestrus. Preparations of follicle wall and isolated theca interna and granulosa cells were analyzed for PGHS-2 protein and mRNA by immunoblot and Northern blot, respectively. Immunohistochemistry was used to document the in situ localization of PGHS-2 protein, and follicular fluid concentrations of prostaglandin (PG) E2 and PGF(2α) were determined to monitor changes in PG synthetic activities. Results showed that PGHS-2 mRNA (4.0 kilobases) and protein (74 000 M,) were absent in preovulatory follicles 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 immunohistochemical analyses revealed that PGHS-2 protein was selectively induced in granulosa cells. Follicular fluid concentrations of PGE2 and PGF(2α) increased significantly (p < 0.01) between 0 and 24 h after estrus (from 2.8 ± 0.2 to 87.9 ± 30.9 ng/ml for PGE2; from 0.05 ± 0,02 to 68.9 ± 23.6 ng/ml for PGF(2α)). Collectively, these results clearly demonstrate that the induction of PGHS-2 in bovine preovulatory follicles is a physiological event that occurs after the endogenous LH surge.