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      Renal Potassium Handling in Aging Rats

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

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          Author and article information

          Kidney Blood Press Res
          Kidney and Blood Pressure Research
          S. Karger AG
          06 February 1999
          : 21
          : 6
          : 425-431
          Laboratório de Pesquisa Básica, Disciplina de Nefrologia, Faculdade de Medicina, Universidade de São Paulo (LIM–12 HC–FMUSP, São Paulo, Brazil
          25895 Kidney Blood Press Res 1998;21:425–431
          © 1998 S. Karger AG, Basel

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          Tables: 4, References: 39, Pages: 7
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