Endothelium-derived relaxing and contracting factors during the early neonatal period.

The interaction and relative potency of nitric oxide, an endothelium-derived relaxing factor, and endothelin- I, an endothelium-derived contracting factor, may be important in the transition from fetal to extrauterine life. The change in level of nitric oxide during the early neonatal period has not been measured. Accordingly, the serum levels of nitric oxide metabolites (the sum of nitrite and nitrate) and plasma endothelin-l were determined in 20 healthy neonates at birth, at 12 and 24h postnatally, and at the age of 5 d. The lowest serum concentration of nitric oxide metabolites was observed at birth (26.2 ± 9.1 μmo1 l -1 , mean ± SD) and increased with age, whereas the highest plasma concentration of endothelin -1 was observed at birth (14.0 ± 6.7 pg ml -1 ) and decreased with age. These changes suggest that nitric oxide and endothelin-l play roles in the circulatory adaptation of the neonate to extrauterine life.