Effect of methylene blue on the vasodilator action of inhaled nitric oxide in hypoxic sheep

Abstract

We have examined the effect of methylene blue 4 mg kg-1 on the pulmonary vasodilator action of inhaled nitric oxide (8, 32, 128 and 512 volumes per million) in nine sheep with pulmonary hypertension induced by hypoxia (F1o2 = 0.12). The dose-response to nitric oxide was unchanged by methylene blue, but increased cardiac output was noted (P<0.01). These results indicate that methylene blue may not inhibit the action of nitric oxide on guanylate cyclase, as suggested previously, and that treatment of methaemoglobinaemia occurring during therapeutic inhalation of nitric oxide with methylene blue may not block the vasodilator effect of nitric oxide on the pulmonary vasculature. © 1994 British Journal of Anaesthesia.