Inhibition of Nitric Oxide: Effects on Interleukin-lβ-Enhanced Ovulation Rate, Steroid Hormones, and Ovarian Leukocyte Distribution at Ovulation in the Rat1

Abstract

The ovulatory process resembles an inflammatory reaction with an infiltration of leukocytes, production of inflammatory mediators such as cytokines, and a general edema and hyperemia. Nitric oxide (NO), a potent vasodilator and the main mediator of macrophage tumoricidal and bacteriocidal activities, is known to participate in inflammatory reactions and has been shown to mediate the interleukin-1 beta (IL-1 beta)-directed tissue-remodeling events within the ovary. The regulation by NO of ovulation rate, leukocyte distribution, and steroid release in the rat ovary was investigated through use of a combination of in vivo and in vitro models of ovulation and a competitive inhibitor, N-omega-nitro-L-arginine methyl ester (L-NAME), of the NO synthase (NOS) enzyme. Subcutaneous L-NAME (1.5 x 10(-4) mol/kg) administration significantly reduced the in vivo ovulation rate of eCG/hCG-primed rats (L-NAME-treated: 10.6 +/- 1.8 [mean +/- SEM] oocytes per ovary [O/O], 11.0 +/- 1.2 rupture sites per ovary [RS/O]; saline-treated: 18.0 +/- 1.8 O/O, 19.4 +/- 1.1 RS/O; p < 0.01) at 20 h post-hCG. These results were reflected in vitro, where addition of L-NAME (3.5 x 10(-5) mol/L) to LH (0.1 microgram/ml)-perfused ovaries decreased ovulation rate from 8.2 +/- 1.6 to 2.7 +/- 1 ovulations per ovary (p < 0.05) and simultaneously decreased nitrite accumulation at the completion of perfusions from 16.5 +/- 1.9 to 4.1 +/- 0.5 nmol/ml (p < 0.001). The addition of L-NAME to LH+IL-1 beta (4 ng/ml)-perfused ovaries decreased ovulation rate from 15.2 +/- 2.4 to 0.8 +/- 0.8 ovulations per ovary (p < 0.001) and simultaneously decreased nitrite accumulation at 22 h from 22.8 +/- 2.2 to 1.9 +/- 0.6 nmol/ml (p < 0.001). Studies analyzing and manipulating perfusion flow rate indicated that the L-NAME effects on ovulation rate are primarily due to a reduction in flow rate resulting from inhibition of NO, which may be a consequence of the known vasoconstrictor effects of NOS inhibitors. The observed reduction of in vivo ovulation rate by NO inhibition at 20 h post-hCG was associated with a significant reduction in thecal MCA149+ neutrophils at 12 h post-hCG, the expected time of ovulation (L-NAME-treated: 98.4 +/- 9.2 cells per thecal area; saline-treated: 211.5 +/- 11.5 cells per thecal area; p < 0.001), while ED1+ monocytes/macrophages underwent similar but nonsignificant changes. Plasma (20 h post-hCG) and perfusate progesterone were not different with L-NAME treatment, while perfusate estradiol levels were markedly reduced upon addition of L-NAME, suggesting a role for NO in ovulation but not in the process of luteinization. In summary, deprivation of NO by use of the competitive inhibitor, L-NAME, led to fewer ovulations, reduced accumulation of nitrite, a decreased neutrophil count in the theca of preovulatory follicles, and reduced estradiol secretion, while progesterone release remained unaffected. The NO pathway may therefore play an important role in the regulation of ovulation and the mediation of IL-1 beta's pro-ovulatory effects. There ar...

Changes in Nitric Oxide Synthase Activity in the Ovary of Gonadotropin Treated Rats. The Role of Nitric Oxide during Ovulation.

“…There are reports suggesting iNOS involvement in the ovulatory process [7,8]. Current reports indicate that IL-1, which plays an important role in ovarian function [22,28,29], utilizes NO to influence the ovarian cells [30][31][32]. The IL-1fi mRNA expression in the ovary shows a narrow peak at 6 h after hCG injection [33].…”

Detection of Interleukin-1.BETA. in Sera and Colostrum of Dairy Cattle and in Sera of Neonates.

“…IL-1β mRNAs were detected only in cells from milk collected during 20 days before and 2-3 to undetectable level after parturition. Moreover, IL-1β has been reported to involve with regulation of progesterone [1,13,17,22] which is essential for maintaining pregnancy [19]. Therefore, presence of IL-1β in sera of healthy mature dairy cattle is considered as physiologically normal condition associated with reproduction.…”

Nitric oxide synthase activity and progesterone release by isolated corpora lutea of rabbits in the early and mid-luteal phases of pseudopregnancy are modulated differently by prostaglandin E-2 and prostaglandin F-2alpha via adenylate cyclase and phospholipase C

“…In the past few years, NO has also emerged as a regulator of multiple functions within the reproductive system (Shukovski & Tsafriri 1995, Bonello et al 1996, Yamauchi et al 1997, and several findings suggest that it may have a significant role in the control of steroidogenesis in both ovary and testes (Adams et al 1992, Welch et al 1995, Olson et al 1996, Hesla et al 1997, Jablonka-Shariff & Olson 1997, Pomerantz & Pitelka 1998, Vega et al 1998.…”