Nitric oxide decreases lung liquid production via guanosine 3',5'-cyclic monophosphate.

We studied the role of cGMP in nitric oxide (NO)-induced changes in lung liquid production (J(v)) in chronically instrumented fetal sheep. Forty-five studies were done in which J(v) was measured by a tracer dilution technique. Left pulmonary arterial flow (Q(lpa)) was measured by a Doppler flow probe. There were two series of experiments. In the first, we gave 8-bromo-cGMP, a cGMP analog, by either the pulmonary vascular or intraluminal route; in the second, we used agents to inhibit or enhance endogenous cGMP activity. When infused directly into the pulmonary circulation, 8-bromo-cGMP significantly increased Q(lpa) but had no effect on J(v). Conversely, when instilled into the lung liquid, 8-bromo-cGMP had no effect on Q(lpa) but significantly reduced J(v). Inhibition of guanylate cyclase activity with methylene blue totally blocked, whereas phosphodiesterase inhibition with Zaprinast significantly enhanced, the effect of instilled NO on J(v). Thus the reduction in lung liquid caused by NO appears to be mediated by cGMP, perhaps through a direct effect on the pulmonary epithelium.