QUANTITATION OF CORTISOL (F) PRODUCTION AND ELIMINATION RATES IN PREMATURE AND TERM NEONATES: EVIDENCE FOR PULSATILE SECRETION

Abstract

Pulsatile secretion of cortisol has not been documented in the newborn infant. Using repeated blood sampling and deconvolution analysis, we investigated F secretory and elimination dynamics in a clinically stable group of 5 premature [gestational age (GA) 24-34 wk] and 5 term neonates. Blood samples were obtained through umbilical arterial cannulae at 15-min intervals for a 6-h period. All plasma F determinations were >55 nmol/L (2.0 μg/dL), and pulsatile F secretion was observed in all infants. On average, 4 ± 1 discrete F secretory episodes were detected during the study. No significant differences were noted between the 2 groups of subjects with regard to 6-h mean plasma F, plasma corticosteroid-binding globulin, F secretory burst frequency, mass of F secreted per burst, F production rate (FPR) or plasma F half-life. However, the premature infants had a significantly longer F secretory burst half-duration (p = 0.007) and a lower maximal F secretory rate (p = 0.018) than the term infants. The 2 most premature infants had significantly greater mean plasma F and FPR than the other 3 premature and all the term infants. Extrapolating to 24 h and correcting for distribution volume of F and for body surface area, we estimate FPR to be approximately 17-24 nmol/m2/24 h (6.6-8.8 mg/m2/24 h) for neonates of ≥34-wk GA. These values are consistent with estimates of FPR in older children and adults determined using either deconvolution analysis or stable isotope-dilution methods.