Changes in urinary 6beta-hydroxycortisol/cortisol ratio after birth in human neonates.

OBJECTIVE

Urinary 6beta-hydroxycortisol/cortisol (6beta-OHF/C) ratio was measured in human neonates to assess the CYP3A enzyme activity.

METHODS

Urinary 6beta-OHF/C ratio was determined on the day of birth in 94 neonates including those born prematurely. In addition, changes in the ratios after birth were also determined in 81 neonates.

RESULTS

On the day of birth, a significant positive correlation was found between urinary 6beta-OHF/C ratios and gestational age (r = 0.476) and birth weight (r = 0.283). There was no gender difference in the urinary 6beta-OHF/C ratios in human neonates. Furthermore, delivery modes such as cesarean section and vaginal delivery did not appear to affect the urinary 6beta-OHF/C ratio. The mean ratio of urinary 6beta-OHF/C observed in 39 mature neonates (more than 37 weeks of gestational age) was higher than that observed in adults (16.5 vs 9.9). Within 5 days after birth, the ratio rapidly decreased to less than that in adults. In contrast, the mean ratio of urinary 6beta-OHF/C observed in 42 premature neonates (under 37 weeks of gestational age) was significantly lower than that observed in mature neonates (5.3 vs 16.5) and was virtually unchanged during the 14-days after birth. Therefore, no significant difference was observed in the mean ratio of urinary 6beta-OHF/C between mature and premature neonates at 5 days after birth.

CONCLUSION

From these results, it was concluded that on the day of birth, mature neonates might possess a higher activity of CYP3A enzyme compared with premature neonates, and that the CYP3A enzyme activity in mature neonates might be promptly changed at an early stage after birth.