Extrarenal action of the adrenal cortex on electrolyte metabolism in nephrectomized and nephrectomized-eviscerated rats

An extrarenal mechanism of potassium adaptation

Rats fed a diet high in potassium for several days survive an acute load of potassium that is lethal to animals on a regular diet. Previous data suggested that this survival occurred because of enhanced kaluresis. Although increased urinary excretion may occur, the major mechanism of this potassium adaptation phenomenon has been found to be extrarenal. Despite nephrectomy just before study, rats previously fed a high potassium diet maintained lower plasma potassium concentrations for at least 2 hr after an acute potassium load than did rats fed a regular diet. Prior adrenalectomy abolished adaptation. Furthermore, rats fed a low sodium diet as an alternative stimulus to aldosterone secretion demonstrated adaptation to potassium loading, as did adrenalecomized rats given large doses of deoxycorticosterone for several days. Adrenalectomy just before the test load of potassium did not abolish adaptation nor did a large dose of aldosterone at that time reproduce it. These data indicate that adaptation is dependent on a chronic increase in aldosterone secretion. The extra potassium removed from the extracellular fluid by adapted rats was not lost into the gastrointestinal tract. It is concluded that more rapid lowering of plasma potassium after acute potassium loads by adapted rats is due to enhanced uptake of potassium by one or more tissues stimulated by chronic aldosteronism.

THE EFFECT OF ALDOSTERONE ON ELECTROLYTES IN MUSCLE, KIDNEY CORTEX, AND SERUM

This investigation was carried out on 128 young rats maintained on diets varying in sodium and potassium content. For all experiments the rats were divided into at least three groups: intact, adrenalectomized (ADX), and ADX given dl-aldosterone (10 or 25 μg) daily for 5 days. In rats on a normal diet serum Na fell from 151 to 134 meq/l. and serum K rose from 7 to 11 meq/l. as a result of adrenalectomy; muscle Na decreased from 119 to 97 meq/kg dry weight and muscle K increased somewhat. In general, kidney cortex Na and K changed in the same direction as the muscle cations. On all high-Na diets muscle Na increased in ADX rats while serum Na remained constant. Tissue K changes were somewhat more variable than alterations in tissue Na. The principal finding was that the administration of aldosterone prevented most of the tissue cation changes caused by adrenalectomy regardless of their direction. Thus a dual control of tissue electrolytes by the hormone is suggested, namely that aldosterone might control tissue cation concentrations indirectly through its influence on plasma levels, and also directly by inhibiting the cellular sodium pump.