Nitric oxide exposure inhibits endothelial NOS activity but not gene expression: A role for superoxide

A. Macduff Sheehy, Michael A. Burson, Stephen M. Black

Research output: Contribution to journalArticlepeer-review

34 Scopus citations


Recent studies have characterized a rebound pulmonary vasoconstriction with abrupt withdrawal of inhaled nitric oxide (NO) during therapy for pulmonary hypertension, suggesting that inhaled NO may downregulate basal NO production. However, the exact mechanism of this rebound pulmonary hypertension remains unclear. The objectives of these studies were to determine the effect of NO exposure on endothelial NO synthase (eNOS) gene expression, enzyme activity, and posttranslational modification in cultured pulmonary arterial endothelial cells. Sodium nitroprusside (SNP) treatment had no effect on eNOS mRNA or protein levels but did produce a significant decrease in enzyme activity. Furthermore, although SNP treatment induced protein kinase C (PKC)-dependent eNOS phosphorylation, blockade of PKC activity did not protect against the effects of SNP. When the xanthine oxidase inhibitor allopurinol or the superoxide scavenger 4,5-dihydroxy-1- benzene-disulfonic acid were coincubated with SNP, the inhibitory effects on eNOS activity could be partially alleviated. Also, the levels of superoxide were found to be elevated 4.5-fold when cultured pulmonary arterial endothelial cells were exposed to the NO donor spermine/NO. This suggests that NO can stimulate xanthine oxidase to cause an increase in cellular superoxide generation. A reaction between NO and superoxide would produce peroxynitrite, which could then react with the eNOS protein, resulting in enzyme inactivation. This mechanism may explain, at least in part, how NO produces NOS inhibition in vivo and may delineate, in part, the mechanism of rebound pulmonary hypertension after withdrawal of inhaled NO.

Original languageEnglish (US)
Pages (from-to)L833-L841
JournalAmerican Journal of Physiology - Lung Cellular and Molecular Physiology
Issue number5 18-5
StatePublished - May 1998
Externally publishedYes


  • Enzyme inhibition
  • Nitric oxide synthase
  • Phosphorylation
  • Protein

ASJC Scopus subject areas

  • Physiology
  • Pulmonary and Respiratory Medicine
  • Physiology (medical)
  • Cell Biology


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