Short-term effect of aldosterone on Na-K-ATPase in single nephron segments.

One of the theories proposed to explain the action of mineralocorticoids on target tissues attributes their effect on cation transport to stimulation of the "sodium pump." To test this hypothesis we evaluated the short-term effect of aldosterone on Na-K-ATPase in discrete nephron segments microdissected from kidneys of adrenalectomized animals. Na-K-ATPase activity measured in proximal and distal nephron segments from adrenalectomized as well as intact mice remained unchanged 1 or 3 h after a single injection of D-aldosterone (10 micrograms/100 g body wt i.p.). Similarly, no effect of aldosterone could be demonstrated in experiments in vitro, in which tubules from adrenalectomized mice and rabbits were incubated (90 min, 37 degrees C) in the presence of physiologic or pharmacologic concentrations of the hormone (3.10(-10) to 3.10(-6) M). These studies did not show an effect of aldosterone on isolated tubule Na-K-ATPase within the time interval in which this hormone alters tubular cation transport and therefore do not support the "pump theory" of mineralocorticoid action.