Aims: To assess CYP3A enzyme activity in human neonates by measuring the urinary 6beta-hydroxycortisol/cortisol (6beta-OHF/C) ratio.
Methods: Fifty-six mature male neonates with normal delivery, seventeen of their mothers and twenty-four healthy non-pregnant young women participated in this study. Urinary 6beta-OHF/C ratio was determined on the day of birth in neonates and their mothers. In addition, changes in the ratio after birth were determined in neonates.
Results: On the day of birth, the urinary 6beta-OHF/C ratio of neonates was significantly higher than that of their mothers (20.5 vs 6.9). In contrast, no significant difference was observed in the mean ratio of urinary 6beta-OHF/C between women with and without pregnancy (6.9 vs 9.0). The urinary 6beta-OHF/C ratio after birth was decreased day by day in neonates.
Conclusion: These results indicate that the high urinary 6beta-OHF/C ratio in mature neonates on the day of birth is independent of the activity of CYP3A enzyme in their mothers.