Urinary nitrite excretion in premature infants: effects of transfusion or indomethacin.

Urinary nitrite excretion, an index of L-arginine-dependent nitric oxide formation, was quantified daily for two weeks, in very low-birth-weight (< 1500 g) premature infants. A transient 52% reduction in nitrite excretion was noted on the day of transfusions (54 +/- 10 versus 26 +/- 6 mumol/mmol creatinine, before and during transfusion, respectively, n = 24, p < 0.02). Indomethacin administration in six infants was associated with a dramatic increase in nitrite excretion from a basal median value of 3 to 76 mumol/mmol creatinine (p < 0.05). Nitrite excretion returned to baseline on day 3 after indomethacin administration. In two infants who received indomethacin and transfusions on the same day, the stimulatory effect on nitrite excretion by indomethacin overwhelmed any depressive effect of transfusions. These results suggest that L-arginine utilization is influenced by common therapeutic strategies in these high-risk infants.