Control of Hypertension with Captopril Affords Better Renal Protection as Compared with Irbesartan in Salt-Loaded Uremic Rats

Dietary salt modifies the blood pressure response to renin-angiotensin inhibition in experimental chronic kidney disease

Chronic kidney disease contributes to hypertension, but the mechanisms are incompletely understood. To address this, we applied the 5/6th nephrectomy rat model to characterize hypertension and the response to dietary salt and renin-angiotensin inhibition. 5/6th nephrectomy caused low-renin, salt-sensitive hypertension with hyperkalemia and unsuppressed aldosterone. Compared with sham rats, 5/6th nephrectomized rats had lower Na⁺/H⁺ exchanger isoform 3, Na⁺-K⁺-2Cl^- cotransporter, Na⁺-Cl^- cotransporter, α-epithelial Na⁺ channel (ENaC), and Kir4.1 levels but higher serum and glucocorticoid-regulated kinase 1, prostasin, γ-ENaC, and Kir5.1 levels. These differences correlated with plasma renin, aldosterone, and/or K⁺. On a normal-salt diet, adrenalectomy (0 ± 9 mmHg) and spironolactone (-11 ± 10 mmHg) prevented a progressive rise in blood pressure (10 ± 8 mmHg), and this was enhanced in combination with losartan (-41 ± 12 and -43 ± 9 mmHg). A high-salt diet caused skin Na⁺ and water accumulation and aggravated hypertension that could only be attenuated by spironolactone (-16 ± 7 mmHg) and in which the additive effect of losartan was lost. Spironolactone also increased natriuresis, reduced skin water accumulation, and restored vasorelaxation. In summary, in the 5/6th nephrectomy rat chronic kidney disease model, salt-sensitive hypertension develops with a selective increase in γ-ENaC and despite appropriate transporter adaptations to low renin and hyperkalemia. With a normal-salt diet, hypertension in 5/6th nephrectomy depends on angiotensin II and aldosterone, whereas a high-salt diet causes more severe hypertension mediated through the mineralocorticoid receptor.NEW & NOTEWORTHY Chronic kidney disease (CKD) causes salt-sensitive hypertension, but the interactions between dietary salt and the renin-angiotensin system are incompletely understood. In rats with CKD on a normal-salt diet targeting aldosterone, the mineralocorticoid receptor (MR) and especially angiotensin II reduced blood pressure. On a high-salt diet, however, only MR blockade attenuated hypertension. These results reiterate the importance of dietary salt restriction to maintain renin-angiotensin system inhibitor efficacy and specify the MR as a target in CKD.

Renal functional deterioration is not affected by the magnitude of sodium consumption in a normotensive model of moderate renal failure

BACKGROUND/AIMS

High sodium consumption has been repeatedly reported to exert deleterious effects on severe chronic renal failure progression, mainly via glomerular mechanisms. However, the role of high sodium intake in renal function deterioration in a model of moderate chronic tubulointerstitial disease has not yet been addressed. We evaluated the effects of exaggerated dietary sodium and the resultant increase in proteinuria on renal function deterioration in experimental tubulointerstitial disease in rats.

METHODS

In 48 Sprague-Dawley rats, moderate renal failure (approximately 50% of normal glomerular filtration rate) was induced by administration of lithium chloride in drinking water. The animals were divided into three groups fed low (<0.2% Na(+)), normal (0.5% Na(+)), or high (8% Na(+)) sodium diets.

RESULTS

Animals in all groups remained normotensive with a similar course of GFR downslope and 100% survival, irrespective of sodium regimen. Rats consuming high sodium diets developed significantly greater proteinuria compared to their counterparts fed normal or low sodium chow.

CONCLUSIONS

(1) Deterioration of renal function in a lithium-induced model of normotensive moderate chronic renal failure was not affected by dietary sodium. (2) Unlike in some other human or experimental renal failure models, the magnitude of proteinuria had no adverse effect on the progression of renal deterioration.