Infusions with molsidomine and isosorbide-5-mononitrate in congestive heart failure: Mechanisms underlying attenuation of effects

The use of nitrates for treatment of heart failure is encumbered by tolerance, caused by whatever mechanism, which has been reported only in a few instances with sydnonimines. Accordingly, we compared molsidomine (6 mg/h) and isosorbide-5-mononitrate (3.75 mg/h) with respect to maximal hemodynamic effects, rapidity and extent of attenuation, and underlying mechanisms by means of constant infusions over 24 h each in 15 patients with chronic congestive heart failure (NYHA II-III) with a placebo-controlled, double-blind, randomized, crossover protocol. Hemodynamic measurements and determinations of neurohormones were performed at baseline and at 2, 8, and 24 h after the beginning of infusions. With molsidomine, reductions of diastolic pulmonary artery pressure by 29% (p < 0.001), by 24% (p < 0.01), and by 24% (p < 0.01) versus placebo were found at 2, 8, and 24 h, which amounted to 19% (p < 0.01), 10% (NS), and 14% (NS) with the nitrate. Cardiac output was meaningfully affected only with molsidomine (+5%, NS, at 2 h; +9%, p < 0.05, at 8 h; and +15%, p < 0.05, at 24 h), as was systemic vascular resistance (-13%, p < 0.05; -9%, NS; and -18%, p < 0.01) at the corresponding times. Increases in renin activity amounted to 130% (p < 0.001), 117% (p < 0,001), and 112% (p < 0.001) with molsidomine, and to 14, 16%, and 0 (each NS) with the nitrate at the corresponding times. Hematocrit was reduced by 5% (p < 0.001), 7% (p < 0.001), and 12% (p < 0.01) with molsidomine and by 5% (NS), 5% (p < 0.05), and 5% (NS) with the nitrate. We conclude that neurohumoral counterregulation or fluid shift, which is even more pronounced with molsidomine despite longer-lasting effects, has no essential role in nitrate-tolerance development. With molsidomine, such a role cannot be ruled out, although alternatively, a fluid shift from arterial to the low-pressure arm of circulation during the later course of infusion would be even more likely.