Moderate sodium restriction in hypertensive subjects: renal effects of ACE-inhibition

It has been suggested that AII-mediated renal mechanisms limit the efficacy of moderate sodium restriction in the lowering of blood pressure (BP) in hypertension. We therefore studied renal hemodynamics and sodium handling in nine essential hypertensives in balance on 200 and on a 50 mmol sodium diet, before and during ACE-inhibition (enalapril 10 mg bid for 8 days) in a cross-over fashion. BP was similar on 50 and 200 mmol Na before enalapril, the fall in BP during enalapril was significantly more pronounced on 50 mmol Na. On 50 mmol Na, GFR and filtered Na were significantly lower, and tubular reabsorption was significantly higher than on 200 mmol Na. GFR increased during enalapril in 50 but not on 200 mmol Na. Consequently, the differences in GFR and filtered load elicited by sodium restriction were no longer present during ACE-inhibition. In contrast, the differences in tubular reabsorption between 50 and 200 mmol Na persisted during enalapril. In conclusion, moderate sodium restriction, not affecting BP, can elicit a renal hemodynamic response. As this response is blunted by ACE-inhibition it is probably mediated by AII. This blunting may contribute to the increased sodium sensitivity of BP during ACE-inhibition. The adaptation of tubular sodium reabsorption is not affected by ACE-inhibition.