Ferroxidases and xanthine oxidase in plasma of healthy newborn infants

In the neonatal period, there is a high iron load, while both the level and molar oxidase activity of ceruloplasmin are low. On the other hand, the ne onatal xanthine oxidase (XO) activity is higher than later in life and XO h as a significant iron-oxidizing capacity. We therefore studied the physiolo gical contribution of XO to the ferroxidase activity of the plasma in 20 fu llterm newborn infants. Ferroxidase activity was measured spectrophotometri cally, with Fe++ as substrate. The uric acid formed by XO was assayed by me ans of HPLC, with electrochemical detection. The total ferroxidase activity in the plasma was about one-fourth of the ad ult level and rapidly increased doubling within 3 days after birth. About 9 0% of the plasma ferroxidase activity was due to ceruloplasmin, the remaind er being accounted for by ferroxidase II. The XO activity underwent a 30% ( statistically non-significant) elevation at 24 h, though ferroxidase activi ty attributable to XO was not detected at any time. Accordingly, XO does not seem to add substantially to the total iron-oxidiz ing capacity of the plasma in the neonatal period. The high molar ferroxida se activity is probably of importance at the endothelial cell surface.