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

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, N(G)-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.