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Morphological and physiological responses to aldosterone: time course and sodium dependence.

The time course and Na+ dependence of morphological responses to a physiological elevation of aldosterone were examined in the renal cortical collecting duct. Male Sprague-Dawley rats were adrenalectomized and given a basal replacement infusion of aldosterone and dexamethasone by osmotic minipump. The animals were given additional aldosterone by either intravenous infusion or by a second implanted osmotic minipump for either 5 h or 1, 3, 7, or 14 days. Animals were fed either a Na(+)-replete or a low-Na+ diet. After these treatments we conducted a morphometric analysis on kidneys processed for electron microscopy by standard techniques. Increased aldosterone induced detectable proliferation of the basolateral membrane of principal cells after 24 h. Basolateral membrane continued to increase rapidly through 3 days of exposure and thereafter at a modest rate. Cell area and the surface density of the basolateral membrane were also increased by aldosterone treatment. The morphological response to aldosterone was markedly inhibited by maintaining animals on a low-Na+ diet. Acute exposure to elevated aldosterone levels (5 h) increased K+ secretion by principal cells without alterations in basolateral membrane area. Chronic (greater than 24 h) exposure to aldosterone induces morphological adaptations that are accompanied by further elevations in K+ secretion.