Comparative Effects of Nitroprusside and Nitroglycerin on Platelet Aggregation in Patients with Heart Failure

We studied the effects of nitroprusside and nitroglycerin on in vitro platelet aggregation responses to adenosine diphosphate and epinephrine in order to relate platelet aggregation effects to hemodynamic alterations in man. In heart failure patients, nitroprusside infusion (mean dose, 65 ± 12 μg/min) decreased systemic vascular resistance by 30|X%, as in vitro platelet aggregation and in vivo formation of aggregates declined significantly (p < 0.01). Nitroglycerin therapy (mean dose, 55 ± 7 μg/rnin) did not significantly alter systemic vascular resistance, as in vitro platelet aggregation or in vivo platelet aggregates were unaffected. In other experiments, the direct effects of varying doses of nitroprusside and nitroglycerin (0.01–100 μg/ml plasma) on platelet aggregation were evaluated. With nitroprusside, platelet aggregation decreased markedly at 0.01 μg/ml plasma concentration. A progressive decrease in platelet aggregation with increasing concentrations of nitroprusside was noticed. In contrast, nitroglycerin in therapeutic range did not affect platelet aggregation. However, higher concentrations (>1.0 μg/ml) of nitroglycerin resulted in lower platelet aggregation. These data suggest that antiplatelet aggregation effects of nitroprusside may be, in part, a mechanism of a decline in systemic vascular resistance in heart failure patients.