Alkalosis Stimulates Release of Nitric Oxide (No) and Prostacyclin(Pgi2) From Pulmonary Microvascular Endothelial Cells

Abstract

Alkalosis is a widely practiced therapeutic modality for persistent pulmonary hypertension of the newborn. Yet, little is known about the cellular mechanisms mediating alkalosis-induced pulmonary vasodilation. To determine if alkalosis stimulates release of endothelial-dependent vasodilators, NO and PGI2 production were measured at pH 7.4 and pH 7.7 by enzyme immunoassay for cGMP and 6-keto PGF1α, respectively. Compared with pH 7.4, alkalosis (pH 7.7) caused a 2-fold increase in both basal and bradykinin (BK, 0.1 μM)-stimulated cGMP production in mixed cultures of pulmonary microvascular endothelial cells (EC) and vascular smooth muscle cells. This was inhibited by 0.1 mM nitro-L-arginine (L-NA). In EC, alkalosis also caused a 5-fold increase in basal release and a 50% increase in BK-stimulated release of PGI2, which was inhibited by 0.01 mM indomethacin. Interestingly, L-NA caused partial inhibition of PGI2 release at pH 7.4, but not at pH 7.7. We conclude that alkalosis stimulates production of both NO and PGI2 from pulmonary EC. Furthermore, at pH 7.4, there is a link between the nitric oxide synthase (NOS) and cyclooxygenase (COX) pathways, suggesting a stimulatory role for NO in eicosanoid production. Alkalosis appears to uncouple the interaction between the NOS and COX pathways.