Adrenocortical Steroid Metabolism in Newborn Infants. V. Physiologic Disposition of Exogenous Cortisol Loads in the Early Neonatal Period

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Abstract
Cortisol loads of 5 mg per kg were given intravenously to a group of normal full-term newborn infants. In each case two plasma steroid half-lives were calculated—one based on the plasma Porter-Silber chromogen levels, and the other based on the plasma cortisol levels as determined by an isotope dilution procedure. The half-lives (mean values) determined by each of the methods were prolonged compared with the half-lives in adults. This result indicated a decreased rate of cortisol metabolism in the newborn infant. Urine samples were collected from infants given the cortisol loads, and the pattern of steroid excretion in various extract fractions was determined qualitatively and quantitatively. Steroid glucuronide conjugate excretion was lower than in adults both in terms of the proportion of total daily steroid output and in terms of the percentage recovery of the administered dose in that fraction. It is concluded that the newborn infant probably has a relative insufficiency of both steroid ring-A reducing and steroid glucuronide conjugating enzymes. The possible reasons for these relative enzyme insufficiencies are reviewed.