Sustained nitric oxide exposure decreases soluble guanylate cyclase mRNA and enzyme activity in pulmonary artery smooth muscle

Background. The soluble isoform of guanylate cyclase (sGC) is activated by nitric oxide (NO) to form guanoside 3':5'-cyclic monophosphate (cGMP). Cyclic GMP levels cause smooth muscle relaxation and regulate vascular tone to various vascular beds, including the lung. Under conditions of cytokine excess the inducible synthesis of NO may result in cGMP overproduction, generalized vasodilatation, and septic shock. In the pulmonary bed the opposite response, pulmonary hypertension, may occur. We hypothesized that sGC activity decreases in the face of sustained 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 abundance and enzyme activity in cultured rat pulmonary artery smooth muscle cells. Results. NO caused a prompt rise in extracellular cGMP production. Pretreating cells with NO for greater than or equal to 45 min inhibited subsequent cGMP synthesis. NO-pretreated cells recovered the capacity for cGMP synthesis after removal of NO for 120 min. When actinomycin or cycloheximide was added to NO pretreatment, cells retained cGMP synthetic capacity. NO pretreatment decreased sGC mRNA abundance, but did not totally eliminate it. Conclusion, NO has important regulatory 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 enzyme activity decreases and cGMP production drops significantly. Soluble GC mRNA abundance also decreases and may result in decreased responsiveness of cells to NO with regard to cGMP production. (C) 1998 Academic Press.