The Selective Prostaglandin Endoperoxide Synthase-2 Inhibitor, NS-398, Reduces Prostaglandin Production and Ovulation In Vivo and In Vitro in the Rat1

Abstract

Two isoforms of prostaglandin G/H synthase, PGS-1 and PGS-2, catalyze the formation of prostaglandins (PG). Nonselective PGS inhibitors, e.g., indomethacin, reduce the number of ovulations and PG levels in many animal models. This study evaluated the effects of the selective PGS-2 inhibitor NS-398, compared to indomethacin, on ovulation number and on PG and steroid production both in vivo and in vitro in the rat. NS-398 reduced the synthesis of PGE2 in isolated, LH-stimulated preovulatory follicles incubated in vitro. The inhibition by NS-398 was similar to that of indomethacin. Maximal inhibition was noted from 0.1 microM. Neither progesterone nor cAMP production was affected by NS-398 or indomethacin. The effect of in vivo administration of NS-398 (1, 3, or 10 mg/kg BW, s. c.) to proestrous rats 1 h after the injection of an ovulatory dose of hCG was monitored in follicles extirpated 10 h after hCG. These follicles were incubated in vitro, and NS-398 dose-dependently reduced PGE2 production. The synthesis of cAMP and progesterone was not altered. In separate experiments, the same doses of NS-398 were injected to determine their effect on ovulation in vivo. The number of ovulations was decreased by the highest dose of NS-398. In the in vitro ovarian perfusion model, NS-398 (10 microM) reduced the number of ovulations initiated by LH and isobutylmethylxanthine. Lower doses of NS-398 (0.1 and 1 microM) were less effective. The production of prostanoids (PGE2, PGF2alpha, and 6-keto-PGF1alpha) was reduced in a dose-dependent manner by NS-398. The secretion of steroids was not affected. This study demonstrates that selective inhibition of PGS-2 by NS-398 reduces LH/hCG-stimulated production of prostanoids and the number of ovulations both in vivo and in vitro. These results provide direct evidence to strengthen the role of the inducible, granulosa cell-expressed PGS-2 as one of the key regulators in the ovulatory process and also document that the elevated and perhaps sustained levels of PG are obligatory for ovulation.

Progesterone-regulated genes in the ovulation process: ADAMTS-1 and cathepsin L proteases

“…COX-2 catalyzes the production of prostaglandins known to be necessary for ovulation (38); mice null for COX-2 have severely impaired ovulation (39,40). COX-2 mRNA was undetectable by RT-PCR analysis in ovaries of PMSG-treated PRϩ͞Ϫ and PRKO mice but was induced rapidly by hCG in ovaries of both genotypes (Fig.…”

Gene expression profiling of bovine preovulatory follicles: gonadotropin surge and prostanoid-dependent up-regulation of genes potentially linked to the ovulatory process

“…Accumulating evidence in multiple species including mouse (Lim et al 1997, Davis et al 1999, rat (Mikuni et al 1998, Gaytan et al 2002, sheep (Murdoch et al 1986), pig (Downey & Ainsworth 1980), monkey (Duffy & Stouffer 2002), and cattle (Peters et al 2004) indicates that intrafollicular synthesis of prostanoids in response to the LH surge is critical for the ovulatory process. The cyclooxygenase (COX)-2 enzyme, which catalyzes the rate limiting step in intrafollicular prostanoid synthesis, is induced within the granulosa layer of rat (Sirois et al 1992), equine (Sirois & Dore 1997), and bovine preovulatory follicles (Sirois 1994, Tsai et al 1996 in response to the LH surge.…”

Inhibition of ovulation by a lipoxygenase inhibitor involves reduced cyclooxygenase-2 expression and prostaglandin E2 production in gonadotropin-primed immature rats

“…The inducible type PTGS2 and PGE 2 -EP 2 receptor signaling play crucial roles in proper follicle rupture and cumulus expansion in a murine model of induced ovulation (Hizaki et al 1999, Matsumoto et al 2001, Ochsner et al 2003, Sirois et al 2004b. Pharmacological or genetical inhibition of PTGS2 activity results in potential suppression of ovulation (Espey et al 1986, Lim et al 1997, Mikuni et al 1998a. On the other hand, the involvement of the alternative LOX pathway in ovulation process was first suggested by Reich et al (1983) who demonstrated that chemical inhibition of LOX blunted ovulatory response in gonadotropins-primed immature rats.…”