Nitric oxide regulates ovarian blood flow in the rat during the periovulatory period

Abstract

Background: The aim of this study was to characterize the roles of nitric oxide (NO) on the rat ovarian blood flow (OBF) during the preovulatory period. Methods and results: Immature Sprague-Dawley rats were primed with pregnant mares' serum gonadotrophin (PMSG, 15 IU) and given hCG (15 IU) 48 h later. The ovary was exposed 48-56 h after PMSG, a laser Doppler probe was attached to the ovarian surface and OBF was measured at two time periods: preovulatory (PO) 48 h after PMSG and ovulatory (OV) 6-8 h after hCG. A non-selective NO synthase inhibitor, NG-nitro-L-arginine methyl ester (L-NAME), was injected i.v. (4 and 10 mg/kg) or intrabursally (1 mg/kg). Intravenous administration of L-NAME to OV rats rapidly increased blood pressure and reduced OBF by 30%, which returned to the pretreatment level within 30 min. L-NAME given into the ovarian bursa of both PO and OV rats did not affect blood pressure and reduced OBF by nearly 40%, which remained low throughout the experiment. Intravenous injection of hCG to PO rats increased OBF to 116.1% at 5 min and 133.5% at 30 min in relation to the pretreatment level. When L-NAME was given intrabursally, subsequent hCG injection was without effect. Conclusions: These results indicate that locally produced NO is important for the maintenance and increase of rat OBF during the preovulatory period.