Renal Potassium Handling in Aging Rats

Aging is often related to electrolyte disorders. This study was designed to evaluate the renal capacity for K + handling of aging rats submitted to both extreme situations of K + depletion and K + loading. Aging rats were submitted to metabolic assessment, measurement of plasma aldosterone and determination of Na + ,K + –ATPase and H + ,K + –ATPase activity in the inner medullary collecting duct (IMCD). During K + depletion, aging rats showed low values of urine K + excretion. After 2 weeks of dietary K + restriction, the plasma K + levels of these animals reached 2.9±0.1 mEq/l without acid–base disorders. During K + loading, aging rats showed a significant increase in urinary K + excretion, with plasma K + remaining at normal levels (4.7±0.1 mEq/l). Plasma aldosterone levels were low in control aging rats but K + intake modulated the levels of this hormone, with K + depletion reducing it and K + loading significantly increasing it. Na + ,K + –ATPase activity increased only in the initial portion of the IMCD of aging rats after 2 weeks of K + depletion. In the distal portion of the IMCD, Na + ,K + –ATPase activity did not change. H + ,K + –ATPase remained unchanged in both the proximal and distal portions of the IMCD of aging rats. During K + loading, there was no change in Na + ,K + –ATPase or H + ,K + –ATPase activity in the proximal or distal portions of the IMCD of aging rats. This study suggests that the senescent kidney responded to K + conservation and excretion under the two extremes of low and high K + intake.