Inappropriate secretion of umbilical plasma catecholamines in preterm compared to term neonates

To investigate the gestation and stimulus related catecholamine secretion and degradation at birth free and sulfoconjugated adrenaline, noradrenaline and dopamine were analysed in the umbilical artery and vein of 35 preterm and 75 term neonates. A highly sensitive radioenzymatic assay was used for the determination of free catecholamine levels, sulfoconjugated catecholamines were analysed after addition of 25 mU arylsulfatase type VI. Levels of free catecholamines were significantly lower in preterm as compared to term newborns. Hereby, adrenaline levels significantly correlated with the gestational age, birth weight, and birth length. Sulfoconjugated catecholamine levels were similarly lower, but only sulfoconjugated noradrenaline reached differences of statistical significance. The placental extraction rate of adrenaline and noradrenaline was significantly lower in preterm as compared to term neonates. Only in term but not in preterm neonates, arterial pH- and pCO2-levels significantly correlated with arterial plasma catecholamine levels. Therefore, lower catecholamine levels in preterm compared to term neonates result from lower secretion of catecholamines rather than increased degradation and may contribute to their frequent surfactant deficiency. In addition, the inadequate and diminished catecholamine secretion of preterm neonates may play a significant part in their postnatal adaptation problems like hypoglycaemia, hypothermia and occurrence of wet lungs.