Comparison of the Vasodilatory Effects of Sodium Nitroprusside versus Nitroglycerin

The vasodilatory mechanism of Nitroglycerin (NTG) is similar to Sodium Nitroprusside (SNP) in regards to action on guanosine 3'5' monophosphate (cyclic GMP) via nitric oxide. However, it is unknown whether NTG can achieve the same magnitude of vasodilation in the forearm as SNP. Therefore, the purpose of the study was to evaluate the differences in forearm blood flow (FBF) and forearm vascular conductance (FVC) during escalating infusions of NTG versus SNP at similar concentration doses and rates. We measured FBF using venous occlusion plethysmography (VOP) and Doppler ultrasound in eight young, healthy participants (mean age = 28 ± 2 years) during four forearm volume (FAV) specific doses (0.25, 0.5, 1, 2 µg•100mL FAV^-1•min^-1) of SNP and NTG, infused via a brachial artery catheter. There was a significant difference in FVC of SNP versus NTG only at the higher doses as measured by VOP (14.9 ± 1.4 and 18.3 ± 1.5 versus 11.6 ± 1.2 and 12.5 ± 1.2 mL•dL FAV^-1•min^-1•100mmHg^-1). FVC as measured by Doppler Ultrasound unadjusted for FAV was significantly different at the lowest and the higher 2 doses of SNP as compared to NTG (202.1 ± 25.8, 329.4 ± 46.7 and 408 ± 63.5 versus 142.9 ± 22.4, 217.2 ± 18.8 and 247.5 ±18.2 mL•min^-1•100mmHg). SNP induces significantly higher vasodilatory actions as compared to NTG. However, NTG is comparable in eliciting equivalent vasodilator effects to SNP during low concentration doses when measured by VOP. Importantly, for forearm pharmacology studies, NTG can elicit marked endothelium independent forearm vasodilation.

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