Nitric Oxide in Treatment of Persistent Pulmonary Hypertension of the Newborn

The gas nitric oxide (NO) inhaled in very low concentrations, for approximately a day or two, appears to be lifesaving in infants with persistent pulmonary hypertension of the newborn (PPHN). It is, indeed, remarkable that an oxide of nitrogen, a precursor to toxic nitrogen oxides often found in polluted air, is effective against this potentially le thal neonatal disorder. We are beginning to under stand that the basis for its effectiveness lies in the facts that the pulmonary hypertension is caused by a virulent form of smooth muscle constriction within pulmonary arterioles and that NO is an ex tremely powerful relaxant of smooth muscle, even in picomolar concentrations. Often, when an im portant biologic function is performed by an ex tremely small amount of an agent, the agent is re lated to a control mechanism normally used by the body. Such is the case for NO, which is normally produced by the endothelial lining cells of the ar teries and quickly diffuses into the smooth muscle layer where it reduces vascular tone. Because the control of vascular tone and hence the diameter of blood vessels is of crucial importance for blood cir culation, health, not only of the neonate, but of us all, may depend in part on the proper function of the NO system. Although our understanding of the chemistry, physiology, pharmacology, and patho physiology of NO has only recently developed, we cannot forget the heritage we owe to earlier medi cal researchers.