Relationship Between Adrenal Steroids and Renal Na-K-ATPase. Effect of Short-term Hormone Administration on the Rat Cortical Collecting Tubule

Mineralo- and glucocorticoids stimulate renal Na-K-ATPase activity if given over a few days, but their immediate effect on the enzyme (i.e. within the time period required to alter electrolyte transport) remains controversial. We evaluated the short-term (3 h) in vivo effect of physiologic and pharmacologic doses of the natural glucocorticoid (corticosterone) and mineralocorticoid (aldosterone), and of a semisynthetic glucocorticoid (dexamethasone) on Na-K-ATPase activity in cortical collecting tubules microdissected from adrenalectomized rats. This nephron segment was chosen because it is a major target site for both classes of corticoids. Neither corticosterone (0.006, 0.6, and 5 mg/100 g body wt, IM), nor dexamethasone (5 mg/100 g body wt, IM) or aldosterone (10 micrograms and 50 micrograms, IV) altered significantly Na-K-ATPase activity in the cortical collecting tubule of these animals 3 h after administration. These results confirm our previous observations in the mouse, and suggest that the enhancing effect of corticosteroids on the renal enzyme seen after longer intervals represents a secondary phenomenon, possibly related to augmentation of the sodium load presented to the pump.