Changes in intrafollicular pressure in the rat ovary by nitric oxide and by alteration of systemic blood pressure

Background: ovulation is associated with degradation of the follicular apex vasodilatation and increased permeability of ovarian vessels. These change s may maintain or increase intrafollicular pressure (IFP) at ovulation to c ause rupture of the follicular wall. Objective: to investigate the possible regulation of IFP during the ovulatory process. Study design: immature Spr ague-Dawley rats were primed with pregnant mare serum gonadotrophin (PMSG; 10 IU) and given hCG (10 IU) 48 h later. The ovary was exposed 48-60 h afte r PMSG, micropipette inserted into the Graafian follicle and the IFP measur ed at three time periods: preovulatory (PO) 48 h after PMSG; midovulatory ( MO) 4-7 h after hCG; late ovulatory (LO) 9-12 h after hCG. The offset of th e nitric oxide synthase (NOS) inhibitor L-arginine methyl ester (L-NAME), t he alpha (1)-adrenoceptor agonist phenylephrine and the beta -adrenoceptor agonist isoprenaline were tested. Results: phenylephrine given i.v. increas ed the systemic blood pressure, and significantly decreased the IFP in the LO phase (78% of pre-treatment value). Local administration of phenylephrin e or isoprenaline (1 ml of 1.5-15 muM) by superfusion over the ovary did no t change the IFP Local administration Of L-NAME (1 ml of 2 muM) significant ly lowered (P < 0.05) the IFP in the MO and LO phases, but was without effe ct in the PO phase. Conclusion: this study reveals that IFP regulation may be related to changes of the systemic blood pressure and that NO may be one local ovarian mediator in IFP regulation. (C) 2001 Elsevier Science Irelan d Ltd. All rights reserved.