Effects of age, feeding regimen, and glucocorticoids on catecholamine and cortisol excretion in preterm infants

Background. The sympathoadrenal system is important in maintaining normal p hysiologic functioning in infants and increased output also can reflect str ess. We sought to determine the effects of age, feeding regimen, and glucoc orticoids on catecholamine and cortisol excretion in preterm infants and to assess whether a particular strategy of feeding enhanced sympathoadrenal d evelopment or was stressful. Methods: Preterm infants (26-30 wk gestation; n = 171) were assigned randomly to begin trophic feedings from day 4 throug h 14 (trophic group) or to start feedings at day 15 (standard group) with f eedings administered either by bolus every 3 hours (bolus) or continuously over 24 hours (continuous). At 10, 28, 40, 50, and 60 days of age, urine wa s collected continuously for 6 hours for measurement of catecholamines (nor epinephrine, epinephrine, dopamine), cortisol, and creatinine. Data were av ailable for 98 infants. Results. Norepinephrine excretion increased with po stnatal age. The increase with age was significantly greater in the trophic group compared with that in the standard group. Epinephrine excretion did not change with age, and there were no differences between trophic and stan dard groups. Dopamine excretion increased with age but was similar between trophic and standard groups (borderline significantly greater in the trophi c group). Cortisol excretion increased with age and also was similar betwee n trophic and standard groups. There was no effect on catecholamine or cort isol excretion of bolus vs continuous feedings, antenatal or postnatal cort icosteroids, gestational age at birth, age at which full feedings were atta ined, or use of human milk compared with preterm formula. Conclusions: The greatest determinant of catecholamine and cortisol excretion is postnatal a ge. Feeding method, type of feeding, and glucocorticoid administration in t he amounts customarily used have little significant effect on catecholamine or cortisol excretion. The apparent link between early feeding and norepin ephrine (and possibly dopamine) excretion warrants further investigation.