The aim of this study was to investigate the effect of postnatal systemic dexamethasone on serum leptin, insulin and hormones of the hypothalamic-pituitary-adrenal (HPA) axis in preterm, very low birthweight (VLBW) infants. Nineteen VLBW infants who received a 3 wk dose tapering course of dexamethasone for treatment of bronchopulmonary dysplasia were prospectively enrolled. Blood for hormone assays was collected immediately before the start of the dexamethasone course (T(d-per)), 3 wk after commencement of the drug (T(d-end)) and 2 wk after dexamethasone treatment had been stopped (T(d-post)). In addition, 28 VLBW infants who participated in a concurrent longitudinal leptin study within the same period but did not receive corticosteroid had their serum leptin and insulin concentrations serially monitored. Blood specimens for the latter group of infants were obtained at 2 (T(wk-2)), 5 (T(wk-5)) and 7 (T(wk-7)) wk of postnatal age. Serum leptin and insulin at T(d-end) were significantly increased, whereas plasma ACTH and serum cortisol were significantly suppressed compared with the pretreatment (T(d-pre)) levels in the corticosteroid group (p < 0.0001 for leptin and insulin; p < 0.05 and p < 0.001 for ACTH and cortisol, respectively). In contrast, serum leptin and insulin at weeks 5 (T(wk-5)) and 7 (T(wk-7)) did not differ significantly from their respective levels at week 2 (T(wk-2)) in the non-treatment group.
Conclusion: The administration of systemic corticosteroid resulted in significant increases in serum leptin and insulin, but marked suppression of hormones of the HPA axis. The effect of dexamethasone on the "adipoinsular" and HPA axes was transient and reversible. The adipoinsular axis in preterm infants is likely to be functional and active at an early stage of human development, and leptin may regulate energy balance in VLBW infants in the early postnatal period. Corticosteroids may, through the adipoinsular axis or its associated pathways, mediate in the regulation of body weight in preterm neonates.