Inhaled sodium nitroprusside. Non-selective reduction of thromboxane analogue-induced pulmonary vasoconstriction in healthy sheep.

Both inhaled nitric oxide (NO) and inhaled prostacyclin have been shown to selectively decrease pulmonary hypertension of various origin. The aim of the present study was to assess the potential of the NO donor sodium nitroprusside (SNP) to elicit selective pulmonary vasodilation. SNP spontaneously liberates nitric oxide in the presence of reducing substances like cysteine or glutathione, ubiquitous in many different tissues. Inhaled as an aerosol in 3 healthy lambs presenting pulmonary hypertension induced by infusion of a thromboxane analogue, low concentrations of SNP (0.02-0.6 mg/ml) revealed no effect at all. In contrast, high concentrations of SNP (1.0-20.0 mg/ml) lowered pulmonary artery pressure in conjunction with systemic arterial hypotension, suggesting systemic resorption of SNP with subsequent release of its nitroso-group. Selective pulmonary vasodilation was never observed. In conclusion, the present results do not support a selective effect of inhaled SNP in the pulmonary circulation.