Measurement of urinary caffeine metabolites reflecting the "in vivo" xanthine oxidase activity in premature infants with RDS and in hypoxic states of children.

Grant et al. have demonstrated that after caffeine intake the ratio of 1-methyluric acid (MU) and 1-methylxanthine (MX) in the urine indicates the total xanthine oxidase (XO) activity of the organism. It has been stated - after having applied this method on premature infants with severe respiration distress syndrome (17 cases) and on children in need of intensive care (18 cases) in the critical phase and during the reparation of the same patients as well, furthermore on so-called shock-tolerant patients (6 cases) and on healthy children (15 cases) - that the total XO activity can increase extremely in severe acute clinical states but a considerable decrease can be detected during reparation while in shock-tolerant states it can become expressively low. The investigations explain properly the favourable XO inhibiting effect of allopurinol demonstrated in states of experimental and clinical shock. The low XO activity observed in shock-tolerant conditions may be the result of intrinsic compensatory mechanisms.