This study aimed to investigate the antiproteinuric and hyperkalemic mechanisms activated by dual renin-angiotensin system (RAS) blockade in renovascular hypertensive rats (2-kidney 1-clip model [2K-1C]). Six weeks after clipping the left renal artery or sham operation (2K), rats were treated with losartan, enalapril, or both drugs for two weeks. We found that 2K-1C rats displayed higher tail-cuff blood pressure (BP), increased non-clipped kidney Ang II concentration, and more pronounced urinary albumin excretion than 2K. BP was decreased by the treatment with either enalapril or losartan, and the combination of both drugs promoted an additional antihypertensive effect in 2K-1C rats. Renal Ang II content and albuminuria were reduced by either enalapril or losartan in monotherapy and restored to control levels by dual RAS blockade. Albuminuria in 2K-1C rats was accompanied by downregulation of the glomerular slit protein podocin, reduction of the endocytic receptors megalin and cubilin, and a marked decrease in the expression of the ClC-5 chloride channel, compared to 2K animals. Treatment with losartan and enalapril in monotherapy or combination increased the expression of podocin, cubilin, and ClC-5. However, only the combined therapy normalized podocin, cubilin, and ClC-5 protein abundance in the non-clipped kidney of 2K-1C rats. Renovascular hypertensive 2K-1C rats had a lower concentration of plasma potassium compared to 2K rats. Single RAS blockade normalized potassium plasma concentration, whereas 2K-1C rats treated with dual RAS blockade exhibited hyperkalemia. Hypokalemia in 2K-1C rats was accompanied by an increase in the cleaved activated forms of α-ENaC and γ-ENaC and the expression of β-ENaC. Combined RAS blockade but not monotherapy significantly reduced the expression of these ENaC subunits in 2K-1C rats. Indeed, double RAS blockade reduced the abundance of cleaved-α-ENaC to levels lower than those of 2K rats. Collectively, these results demonstrate that the antiproteinuric effect of dual RAS blockade in 2K-1C rats is associated with the restored abundance of podocin and cubilin, and ClC-5. Moreover, double RAS blockade-induced hyperkalemia may be due, at least partially, to an exaggerated downregulation of cleaved α-ENaC in the non-clipped kidney of renovascular hypertensive rats.

The present work aimed to compare the effects of monotheraphy versus combined therapy of enalapril and losartan and investigate the mechanisms by which these antihypertensive agents revert proteinuria in 2K‐1C hypertensive rats. To this end, male Wistar rats were subjected to 2K‐1C surgery or sham‐operation (2K). After six weeks, rats were treated with losartan (30mg/Kg/day), enalapril (20mg/Kg/day), losartan+enalapril (20+30mg/Kg/day) or saline by gavage for 14 days. Systolic blood pressure (SBP, mmHg) was higher in 2K‐1C (247±5) than in 2K (129±2, P<0.0001). Losartan (197±6, P<0.05) and enalapril (205±7, n=8, P<0.05) progressively reduced 2K‐1C SBP, with an additional hypotensive effect in the group treated with both drugs (173±16mmHg, P<0.001). Plasma levels of Ang II and TBARS were similar in 2K and 2K‐1C rats and were not changed by the treatments. Albuminuria was remarkably increased in 2K‐1C control rats when compared to 2K control rats. Treatment of 2K‐1C rats with losartan and enalapril similarly reduced albumin excretion when compared to the untreated 2K‐1C. A more pronounced reduction of albuminuria was observed in rats treated with combined therapy. Lucigenin‐derived chemiluminescence was not different in the right and left kidneys of 2K and 2K‐1C rats. Treatments had no effect upon NADPH oxidase activity. The expression of glomerular proteins, including nephrin and podocin, and of proximal tubular protein such as megalin and the Cl/H+ exchanger ClC‐5 were much lower in 2K1C compared to 2K. Treatment with enalapril or losartan partially reverted whereas combined therapy completely restored the expression levels of nephrin and podocin. Taken together, these results suggest that the antiproteinuric effects induced by RAS inhibitors in 2K‐1C rats does not involve inhibition of ROS, but is associated with normalization of the expression of nephrin and podocin in the glomeruli. Grant Funding Source: Supported by FAPESP, CAPES, CNPq, CIHR and Heart and Stroke Foundation of Canada.