Current status of inhaled nitric oxide therapy in the perinatal period

L-Citrulline ameliorates chronic hypoxia-induced pulmonary hypertension in newborn piglets

Newborn piglets develop pulmonary hypertension and have diminished pulmonary vascular nitric oxide (NO) production when exposed to chronic hypoxia. NO is produced by endothelial NO synthase (eNOS) in the pulmonary vascular endothelium using l-arginine as a substrate and producing l-citrulline as a byproduct. l-Citrulline is metabolized to l-arginine by two enzymes that are colocated with eNOS in pulmonary vascular endothelial cells. The purpose of this study was to determine whether oral supplementation with l-citrulline during exposure of newborn piglets to 10 days of chronic hypoxia would prevent the development of pulmonary hypertension and increase pulmonary NO production. A total of 17 hypoxic and 17 normoxic control piglets were studied. Six of the 17 hypoxic piglets were supplemented with oral l-citrulline starting on the first day of hypoxia. l-Citrulline supplementation was provided orally twice a day. After 10 days of hypoxia or normoxia, the animals were anesthetized, hemodynamic measurements were performed, and the lungs were perfused in situ. Pulmonary arterial pressure and pulmonary vascular resistance were significantly lower in hypoxic animals treated with l-citrulline compared with untreated hypoxic animals (P < 0.001). In vivo exhaled NO production (P = 0.03) and nitrite/nitrate accumulation in the perfusate of isolated lungs (P = 0.04) were significantly higher in l-citrulline-treated hypoxic animals compared with untreated hypoxic animals. l-Citrulline supplementation ameliorated the development of pulmonary hypertension and increased NO production in piglets exposed to chronic hypoxia. We speculate that l-citrulline may benefit neonates exposed to prolonged periods of hypoxia from cardiac or pulmonary causes.

Diarrhoea and nitrogen oxides

It is hypothesized that higher indoor nitrogen dioxide levels cause diarrhoea in infants and that this is the result of a direct action of oxides of nitrogen on the gut. This hypothesis is tested by reviewing the reported association between methaemoglobin and diarrhoea in children and two recent reports on indoor air and diarrhoea in infants. The collection of further empirical data is now needed. Studies which measure indoor levels of nitrogen dioxide could usefully collect data on infants symptoms that are not exclusively respiratory. Similarly, studies which are collecting diary information on children's health symptoms should consider collecting data on indoor air quality with respect to the oxides of nitrogen.

Nitric oxide in adult lung disease

Advances in the understanding of nitric oxide as a biological mediator and a therapeutic tool continue to accumulate at a rapid rate. This review provides an update on recent developments pertinent to the role of nitric oxide in adult lung disease. After a brief review of basic nitric oxide biochemistry and physiology, the evidence supporting the role of nitric oxide in the regulation of vascular and airway tone in the normal lung is considered. Clinical studies addressing the pathophysiological role of nitric oxide in pulmonary hypertension, airway disease, and lung injury are reviewed, and the application of inhaled nitric oxide therapy is discussed.