Blunted vasoreactivity in pregnant guinea pigs is not restored by meclofenamate

Abstract

Pregnant women show a reduced pressor responsiveness to angiotensin II, but the mechanism responsible in unclear. We sought to determine whether reduced pressor responsiveness was due to decreased vasoreactivity and the involvement of increased vasodilator prostaglandin production in decreases observed. We found that pregnancy decreased systemic vascular resistance and the systemic vascular resistance response to angiotensin II infusion but not to phenylephrine hydrochloride infusion in awake, unstressed guinea pigs. The decreased systemic vascular resistance response to angiotensin II in the pregnant animals was accompanied by a reduced pressor response. Contractility to phenylephrine hydrochloride and norepinephrine was reduced in aortic rings isolated from pregnant, compared with nonpregnant, guinea pigs. Treatment with meclofenamate, a prostaglandin synthesis inhibitor, did not restore vasoreactivity in either the pregnant animal or the isolated vessel to levels observed in the nonpregnant state. We concluded that pregnancy reduced systemic vascular resistance and vasoreactivity but that mechanisms other than increased vasodilator prostaglandin production were likely responsible.