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 >/=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 large amounts of cGMP. With prolongation of exposure (>/=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.