Nitric oxide and pulmonary circulation.

The aim of this review is to outline the characteristics of the pulmonary circulation in healthy and disease status and the power of exhaled NO (eNO) as a means to assess the involvement of pulmonary circulation in pathological conditions.The discovery of the endocrine role of the endothelium has generated a great interest in its potential regulatory role on the vascular tone of the pulmonary vascular bed. Nitric oxide (NO) mediated-endothelium-dependent relaxation has been demonstrated in pulmonary arteries of animals and humans. The changes in the NO pathway with pulmonary hypertension are not clear. As a matter of fact NO is important in modulating the response to acute hypoxia and the responses to increased flow and to shear stress. The amount of exhaled NO (eNO) of different species may be easily measured reflecting overall NO metabolism from the lung (thus including epithelial, endothelial and other cells activities). The development of pulmonary hypertension secondary to systemic (systemic sclerosis, chronic heart failure) or pulmonary (COPD) diseases appears to be associated with a decrease in eNO production both at rest or during exercise. Chronic inhalation of NO appears to protect against pulmonary hypertension in animal settings.Exhaled NO is growing in interest for its in vivo ability to represent the feature of pulmonary circulation in the pathological condition.