COLLECTING DUCT CHANGES IN POTASSIUM-DEPLETION - EFFECTS OF ACE-INHIBITION

Potassium depletion is associated with a hyperreninemia that may be responsible for some of the renal hemodynamic and functional changes observed in K-deficient states. The present study was designed to evaluate whether interruption of the renin-angiotensin system with enalapril alters the collecting duct changes observed in K depletion. Adrenalectomized male Sprague-Dawley rats were allocated to either a normal (NK) or low-K diet (LK), and they either received enalapril or vehicle for 3 wk. Na:K pump activity (pmol.mm(-1).h(-1)) in microdissected cortical collecting (CCT) and medullary collecting tubules (MCT) was determined at 21 days after group allocations. K depletion had a minimal effect on CCT outer diameter. In contrast, a marked hypertrophy was observed in the MCT diameter (91% increase, P < 0.001) that was significantly attenuated by enalapril treatment (56% increase, P < 0.001 vs. LK). An increase in Na:K pump activity was observed with LK, in the CCT from 497 +/- 47 to 1,089 +/- 83 (P < 0.001) and in the MCT from 489 +/- 36 to 1,396 +/- 45 pmol.mm(-1).h(-1) (P < 0.01). In K-replete rats, enalapril had no effect on Na:K pump activity in either CCT or MCT. Enalapril administration during LK had no effect on the increase in Na:K pump activity in the CCT (1,023 +/- 75 pmol.mm(-1).h(-1), P < 0.001), not different from LK alone. In the MCT, however, enalapril reduced the increment in Na:K pump activity induced by LK (1,116 +/- 39 pmol mm(-1).h(-1), less than the change with LK alone). The attenuation of the augmentation in Na:K pump activity effected with enalapril was similar proportionally to its reduction in the morphological change induced by K depletion. We conclude that angiotensin-converting enzyme (ACE) inhibitors are able to attenuate the morphological and biochemical changes that occur in the collecting duct during K depletion.