Effect of Nitric Oxide Synthase Inhibition on the Uterine Vasculature of the Late-pregnant Ewe

Objectives: We studied the role of nitric oxide in the maintenance of uterine vascular tone during pregnancy.

Study Design: Late-pregnant ewes were instrumented with ultrasonographic flow probes on the left and right main uterine arteries. A catheter was passed retrogradely into 1 uterine artery from a tributary. In 14 animals nitric oxide synthase inhibitor (N omega-nitro-L-arginine methyl ester; L-NAME) was infused at 2 or 20 mg/kg during a 1-minute period into either the main left or right uterine artery.

Results: The nitric oxide synthase inhibitor (20 mg/kg), infused into 1 uterine artery, significantly decreased uterine blood flow (P <.001) bilaterally, increased (P <.05) mean arterial pressure, and decreased heart rate (P <.05). The compound (when infused at 2 mg/kg) also significantly (P <.05) decreased uterine blood flow in the artery ipsilateral to, but not contralateral to, the infusion, with no change in mean arterial pressure and a decrease (P <.05) in heart rate.

Conclusion: During ovine pregnancy, endogenous nitric oxide production contributes to uterine vasodilatation.