Selective Pulmonary Vasodilation Induced by Aerosolized Zaprinast

Background: Zaprinast, an inhibitor of guanosine-3',5'-cyclic monophosphate (cGMP)-selective phosphodiesterase, augments smooth muscle relaxation induced by endothelium-dependent vasodilators (including inhaled nitric oxide NO]). The present study was designed to examine the effects of inhaled nebulized zaprinast, alone, and combined with inhaled NO.

Methods: Eight awake lambs with U46619-induced pulmonary hypertension sequentially breathed two concentrations of NO (5 and 20 ppm), followed by inhalation of aerosols generated from solutions containing four concentrations of zaprinast (10, 20, 30, and 50 mg/ml). The delivered doses of nebulized zaprinast at each concentration (mean +/- SD) were 0.23 +/- 0.06, 0.49 +/- 0.14, 0.71 +/- 0.24, and 1.20 +/- 0.98 mg center dot] kg sup -1 center dot] min sup -1, respectively. Each lamb also breathed NO (5 and 20 ppm) and zaprinast (0.23 +/- 0.06 mg center dot] kg sup -1 center dot] min sup -1) in combination after a 2-h recovery period.

Results: Inhaled NO selectively dilated the pulmonary vasculature. Inhaled zaprinast selectively dilated the pulmonary circulation and potentiated and prolonged the pulmonary vasodilating effects of inhaled NO. The net transpulmonary release of cGMP was increased by inhalation of NO, zaprinast, or both. The duration of the vasodilation induced by zaprinast inhalation was greater than that induced by NO inhalation.