Transport of Uric Acid by the Malpighian Tubules of Rhodnius Prolixus and Other Insects

Urate is transported against an electrochemical gradient into the lumen of the lower Malpighian tubule of Rhodnius. In vivo, higher urate transport rates are induced by the increase in haemolymph urate concentration that follows feeding. The induced rate of transport is sufficient to account for the amount of urate eliminated. In vitro experiments with the tsetse fly Glossina suggest a possible induction of transport as a direct response of the tubule cells to an increase in urate concentration in the surrounding fluid. Urate transport has been shown for Malpighian tubules of insects from several different orders, suggesting that the mechanism is widespread. Insect urate transport differs from that of vertebrates; it is ouabain-insensitive and results in the precipitation of free uric acid instead of urate salts.