Physiologic significance of nitric oxide and endothelin-1 in circulatory adaptation

Background: The purpose of the present paper was to evaluate the physiologi c significance of nitric oxide (NO) and endothelin (ET)-1 in circulatory ad aptation in the neonate. Methods: The serum levels of NO metabolites (NOx; the sum of nitrites and n itrates) and the pll;sma level of ET-1 were determined in 14 healthy full-t erm infants: at 0-6 h, 24 h and 5 days after birth-We measured the heart ra te, the mean systemic blood pressure and the mean pulmonary arterial pressu re, estimated by pulsed Doppler echocardiography, at each time point. Results: The serum concentration of NOx was lowest at birth and increased w ith age. The plasma concentration of ET-1 was highest at birth and decrease d with age. The ratio of NOx to ET-1 was inversely related to the estimated mean pulmonary arterial pressure in the early neonatal period. The ratio o f NOx to ET-1 was not correlated with the systemic blood pressure. Conclusion: increased NO synthesis and decreased production of ET-1 during the early neonatal period may contribute to the decrease in pulmonary arter ial pressure.