Mechanisms of distal-nephron Li(+) reabsorption during dietary K(+) restriction in rats

The mechanism by which dietary K(+) restriction induces distal-nephron Li(+) reabsorption was investigated by administration of bendroflumethiazide (BFTZ) or vehicle in conscious Wistar rats. Changes in fractional excretion of Li(+) following administration of amiloride (DeltaFE(Li)) were used as an index of distal tubular Li(+) reabsorption. The results revealed an absence of distal tubular Li(+) reabsorption in K(+)-replete rats (DeltaFE(Li) = 3. 6+/-2.4%), in contrast to K(+) restriction in which DeltaFE(Li) was 24.0+/-2.7%. The distal tubular Li(+) reabsorption in K(+)-depleted rats was significantly reduced by preadministration of BFTZ (DeltaFE(Li) = 9.2+/-0.9%). The fractions of Li(+) and Na(+) reabsorbed in the amiloride-sensitive segment were different in K(+)-replete rats (9+/-6 vs. 60+/-6%), but similar in K(+)-depleted rats (61+/-5 vs. 73+/-4%). BFTZ administration to K(+)-depleted rats resulted in a proportional decrease in these fractions, suggesting competition between Na(+) and Li(+) for reabsorption in the distal-nephron segment during K(+) depletion. These results are compatible with the hypothesis that during K(+) depletion the reabsorption of Li(+ )in the distal-nephron segment is competitively inhibited by Na(+).