Cortisol (F) is secreted in discrete pulses at approx 65 min intervals in neonates. The aim of this study was to assess the effect of gestational age on such pulsatile F secretion. Blood samples for plasma F were taken via indwelling arterial lines at 15 min intervals for 6 hours in neonates not exposed to antenatal steroids < 7 days before being studied. Clinically stable neonates were studied in the first 9 postnatal days. Characteristics of F secretion were estimated by deconvolution analysis. Neonates were studied in three gestational age groups: < 34 wks (median ga 31 wks, bw 1.57 kg, n=18), 34-36 wks (median ga 35 wks, bw 2.72 kg, n=7) and > 36 wks (median ga 38 wks, bw 3.51 kg, n=9). Pulsatile F secretion was observed in all infants. Data in the Table are given as median and inter-quartile range.

Table 1
Full size table

Extrapolating to 24h, and correcting for volume of distribution of F and body surface area, we estimated median endogenous F production rate for the ga groups < 34 wks, 34-36 wks, and > 36 wks as 5.8, 4.5, and 7.6 mg/m2.24h, respectively. We conclude that F production rate is not influenced by gestational age in clinically stable neonates.