Kaliuretic regulatory factors in the rat

To evaluate the role of aldosterone, plasma potassium, and sodium and urine excretion rates in controlling both total daily potassium excretion and the diurnal cyclic excretion of potassium, we performed experiments on unanesthetized, undisturbed rats kept in a 12-h light/12-h dark environment and fed a liquid diet. Independent variations were imposed on potassium intake, sodium intake, and, in groups of adrenalectomized rats, on aldosterone infusion rates. Potassium intake was 2.6, 10.6, and 18.7 meq/day. Sodium intake was 2.1, 6.7, and 17 meq/day. Aldosterone infusion was 0.1, 0.4, 1, and 10 times a basal rate of 1 microgram.day-1.100 g-1, with constant dexamethasone infusion at 1.43 micrograms.day-1.100 g-1. Twenty-four-hour excretion of potassium and sodium balanced 24-h intake of potassium and sodium regardless of the imposed combination of known regulatory factors. The amplitudes of potassium and sodium excretion during the diurnal cycle were each closely related to the ongoing levels of potassium and sodium intake. Plasma potassium was measured at the peak of the potassium cycle. It is suggested, based on analysis of the results, that when caloric balance was maintained, the amplitude of the diurnal potassium cycle was not importantly influenced by the rates of sodium and urine excretion, and, in addition to effects of aldosterone and plasma potassium concentration, the amplitude was importantly influenced by unspecified, homeostatically effective kaliuretic factors. Adrenalectomized rats receiving subbasal aldosterone replacement rejected the high potassium diet, were anuric, lost weight, and were severely hyperkalemic, observations indicating the necessity of adequate aldosterone for maintenance of potassium homeostasis.