Transfer and dynamics of uric acid in the pregnant rhesus monkey. I. Transplacental and renal uric acid clearances.

Data from the literature suggest that uric acid produced by the fetus could pass across the placenta and contribute to the observed increase in maternal plasma levels of uric acid in preeclamptic pregnancy. To investigate this hypothesis, fetal transplacental and renal uric acid clearances were estimated in 4 term pregnant rhesus monkeys by means of the steady infusion method using 14C-labeled uric acid. Allantoin clearances were determined in one pregnant monkey. Samples of maternal and fetal arterial blood were collected at regular intervals. The total amount of fetal urine produced during the experiment was collected at the end of the experiment. In addition, maternal endogenous renal uric acid and creatinine clearances were measured in 6 term pregnant monkeys. Fetal transplacental uric acid clearances appeared to be almost entirely limited by placental permeability and varied between 3.6 and 8.6 ml X min-1 X kg-1 of fetal weight; fetal renal clearances were between 0.11 and 0.20 ml X min-1 X kg-1. The allantoin clearances were found to be of the same magnitude. Maternal renal clearances of uric acid and creatinine were almost equal (mean 3.2 +/- 0.6 and 3.0 +/- 0.5 ml X min-1 X kg-1 of maternal weight, respectively). Extrapolation of these data to human preeclamptic pregnancy reveals that it is unlikely that fetal uric acid could significantly contribute to the maternal uric acid load.