Possible Association of Xanthine Dehydrogenase/Xanthine Oxidase Activity with Nitric Oxide in vivo

y = 0.83x + 0.37, r = 0.62, p < 0.01 y = 0.58× + 0.47, r = 0.51, p < 0.05 Λ 1·5∏ Λ 1.5-1 0.0 0.5 1.0 1.5 Urinary NOx (mmol/mmol Cr) 0.0 0.5 1.0 1.5 Urinary NOx (mmol/mmol Cr) Fig. 1. Relationship between urinary UA and NOx in term (a) and preterm infants (b). Significant positive correlations are observed in term and preterm subjects. Dear Sir, The final metabolic reactions in purine metabolism involve the oxidation of hypo-xanthine to xanthine and then to uric acid (UA) by the catabolic enzyme xanthine de-hydrogenase/xanthine oxidase (XD/XO) [1]. XD/XO is also a source of production of the oxidants, Oa and ⅝ < ¾ [1, 2]. The mechanisms responsible for the regulation of XD/ XO in vivo remain largely unknown. Recently, we had the opportunity to obtain some evidence for an association between XD/XO activity and nitric oxide (NO) [3] in vivo. Our study group consisted of 35 infants aged 1 month; 17(10 boys and 7 girls) were healthy term infants, and 18 (9 of both sex) preterm infants who were born with a gesta-tional age of 24-32 weeks (mean 29) and a birth weight of 808-1,970 g (mean 1,398). All preterm babies developed respiratory distress just after birth requiring ventilatory support and oxygen supply during the first 2-76 days (mean 15) and 3-90 days (mean 22), respectively; 3 of them were still ventilated at the time of study. Spot urine samples were collected in a bag applied to the perineum. UA was measured spectrophotome-trically using the uricase-peroxidase-coupled reaction. Nitrite/nitrate anions (NOx), stable end products of NO [3, 4], were determined by the brucine method [5]. Urinary excretion of UA and NOx was expressed as a ratio to the urinary creatinine (Cr)