Dissociation of hypertension and renal damage after cessation of high salt diet in Dahl rats

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Conference Proceeding

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BACKGROUND: Every year, thousands of hypertensive patients reduce salt consumption in the efforts to control blood pressure. Most of the studies agreed that about one-third of the patients had an excellent response, one-third had only a modest response, and one-third had little or no response. Irreversibility of high blood pressure is associated with various mechanisms underlying the self-sustaining character of hypertension. We hypothesize that chronic hypertension leads to sustained renal damage and excessive sodium reabsorption, staying even after removing the trigger, caused the initial blood pressure raise.

METHODS: We used Dahl salt-sensitive rats for chronic continuous observation of blood pressure with radiotelemetry in conscious free moving animals. Rats were fed a 4%NaCl diet to induce hypertension, and then the diet was switched back to normal (0.4%NaCl). Patch-clamp analysis was performed in freshly isolated, split-open cortical collecting ducts to characterize activity of epithelial sodium channel (ENaC), responsible for sodium reabsorption in aldosterone-sensitive distal nephron. Flow cytometry, trichrome staining and FITC-inulin clearance estimated immune cell infiltration, renal damage and renal function.

RESULTS: We found that blood pressure increase is reversible if induced by a short 3-day long feeding with 4%NaCl diet. A 3-week long high salt diet develops a sustaining hypertension (MAP ~150 mmHg): switching back to 0.4%NaCl diet slightly reduces blood pressure (to 145 mmHg) next day, but later hypertension progresses, reaching ~158 mmHg. Notably, the self-sustaining phase of hypertension was sensitive to benzamil treatment, which lowered BP to ~136 mmHg. Patch clamp analysis revealed that development of hypertension was accompanied with elevated ENaC activity which also stayed high, despite withdrawal of 4%NaCl diet. A separate subset of experiments demonstrated that dietary salt reduction in hypertensive animals decreases the number of total CD45+CD3+CD4+ and CD45+CD3+CD8+ cells in renal tissues. Also, we found a reduced area of protein casts abundance in the post-salt hypertensive group in comparison with age-matched rats kept on a high salt diet, and improving a glomerular filtration rate in the post-salt period.

CONCLUSION: Based on our earlier publications and current data, we conclude that ENaC activity contributes to both development of salt-sensitive hypertension and its continuation in the absence of high salt challenge. However, dietary salt restriction reduces renal inflammation and damage in hypertensive animals.