SUSTAINED NITRIC-OXIDE EXPOSURE DECREASES SOLUBLE GUANYLATE-CYCLASE MESSENGER-RNA AND ENZYME-ACTIVITY IN PULMONARY-ARTERY SMOOTH-MUSCLE

Background. The soluble isoform of guanylate cyclase (sGC) is activate d by nitric oxide (NO) to form guanoside 3':5'-cyclic monophosphate (c GMP). Cyclic GMP levels cause smooth muscle relaxation and regulate va scular tone to various vascular beds, including the lung. Under condit ions of cytokine excess the inducible synthesis of NO may result in cG MP overproduction, generalized vasodilatation, and septic shock. In th e pulmonary bed the opposite response, pulmonary hypertension, may occ ur. We hypothesized that sGC activity decreases in the face of sustain ed levels of NO. Materials and Methods. We used the NO-donor S-nitroso -acetyl-D-L-penicillamine to study the effects of NO on sGC mRNA abund ance and enzyme activity in cultured rat pulmonary artery smooth muscl e cells. Results. NO caused a prompt rise in extracellular cGMP produc tion. Pretreating cells with NO for greater than or equal to 45 min in hibited subsequent cGMP synthesis. NO-pretreated cells recovered the c apacity for cGMP synthesis after removal of NO for 120 min. When actin omycin or cycloheximide was added to NO pretreatment, cells retained c GMP synthetic capacity. NO pretreatment decreased sGC mRNA abundance, but did not totally eliminate it. Conclusion, NO has important regulat ory effects on cGMP synthesis at the level of enzyme activity and mRNA abundance. NO causes an immediate synthesis of Barge amounts of cGMP. With prolongation of exposure (greater than or equal to 60 min) sGC e nzyme activity decreases and cGMP production drops significantly. Solu ble GC mRNA abundance also decreases and may result in decreased respo nsiveness of cells to NO with regard to cGMP production. (C) 1998 Acad emic Press.