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Nitric oxide modulates human chorionic gonadotropin-induced ovulation in the rabbit
J S Hesla1, S Preutthipan, M P Maguire
1Johns Hopkins University School of Medicine, Baltimore, Maryland, USA.
Objective:
To examine the potential role of the L-arginine:nitric oxide pathway in hCG-induced ovulation in the rabbit.
Design:
Randomized, controlled animal study.
Setting:
University research laboratory.
Intervention(S):
Nitric oxide synthase, the enzyme that produces nitric oxide (NO), was immunohistochemically localized in the ovary. NG-nitro-L-arginine methyl ester (L-NAME), an analogue of L-arginine, which inhibits the enzyme NO synthase, and the inactive D-enantiomer were administered in vivo and/or in vitro via an isolated, perfused ovary preparation during the periovulatory period.
Main Outcome Measure(S):
Rate of follicular rupture (ovulatory efficiency).
Result(S):
Immunohistochemical staining for NO synthase was localized specifically to the granulosa cell layer of the follicle and the endothelium and adventitia of ovarian blood vessels. In vivo administration of L-NAME significantly reduced the percentage of large follicles that ovulated in response to hCG (treated 24.6%, control 68.1%). Similarly, exposure of the in vitro-perfused ovary to L-NAME significantly reduced follicular rupture (treated 32.8%, control 64.2%). In contrast, addition of an equimolar concentration of D-NAME to the perfusion medium had no significant effect on the rate of ovulation (treated 83.3%, control 61.3%).
Conclusion(S):
The stereospecific inhibition of follicular rupture by the arginine analogue suggests that NO production by the ovary is an important feature of the normal physiologic processes of the periovulatory period.