Effects of Nitroglycerin and Nitroprusside on the Uterine Vasculature of Gravid Ewes

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Abstract
The effects of nitroglycerin (TNG) and sodium nitroprusside (SNP) on mean aortic pressure (MAP), uterine blood flow (UBF), uterine vascular conductance (UVC) and pulse rate (PR) were compared when the 2 agents were infused to prevent and treat hypertension induced by norepinephrine (NE) in gravid ewes. When infused alone, TNG, 19 .mu.g/kg per min, decreased MAP 19% and increased PR 33% from control values, but did not significantly change UBF or UVC. SNP, 3 .mu.g/kg per min, decreased MAP 20% and increased PR 43% and did not significantly change UBF or UVC. When given alone, 4 successive 2 min infusions of NE produced dose-related increase in MAP and decreases in UBF, UVC, and PR; values were significantly different from control with the 2 higher doses of NE. Although MAP, UBF and UVC were still significantly changed from control levels when NE was given in the presence of the above infusions of TNG or SNP, MAP was lower and UBF and UVC were higher compared with when NE was given alone. When given to control hypertension induced by a continuous infusion of NE, TNG or SNP produced uterine vasodilatation and significantly increased UBF. TNG and SNP were equally effective in counteracting the maternal hypertension and antagonizing the uterine vascular effect of NE. Apparently TNG and SNP counteract uterine vasoconstriction resulting from .alpha.-adrenergic stimulation and do not produce a shunt of blood flow away from the uterine vasculature when used to control hypertension in gravid ewes.