Hypoxanthine metabolism and transfer in the pregnant rhesus monkey

Fetal metabolic conversion and clearance of hypoxanthine was investigated in five pregnant rhesus monkeys. [14C]hypoxanthine injected into the fetal circulation disappeared rapidly and its metabolic break-down products uric acid and allantoin appeared in fetal plasma and erythrocytes. In amniotic fluid only hypoxanthine could be demonstrated. When [14C] hypoxanthine was infused into the fetal circulation at a constant rate and metabolic conversion to uric acid and allantoin was inhibited with allopurinol, a constant level of hypoxanthine was obtained within 30 min. No uric acid or allantoin was demonstrated, but inosine monophosphate and adenine nucleotides appeared in the fetal erythrocytes. The concentration of adenine nucleotides in the fetal red cells showed a steady increase during the experiments. Total fetal hypoxanthine clearance, calculated in the steady-state from the maternal and fetal arterial concentrations and the amount infused per unit of time varied between 4.2 and 8.4 ml min-1. In two separate experiments maternal blood was incubated with [14C] hypoxanthine and [14C]adenosine. The erythrocytes appeared to be unable to convert hypoxanthine into adenine nucleotides, but adenosine was readily converted into ADP and ATP. There appears to be no preferential uptake of hypoxanthine by the fetal erythrocytes which makes it unlikely that they could serve as carriers in the transport of hypoxanthine.