Abstract P228: Chronically Enhanced Fructose Intake Induces Salt Sensitive Hypertension in Mice and Increases NKCC2 Phosphorylation

Abstract

High fructose consumption is implicated in hypertension and renal damage in humans. The mechanisms for the renal effects of fructose are not clear. In normal rats, a high fructose diet (20%) does not increase blood pressure, but rapidly (one week) induces a salt sensitive increase in blood pressure. NaCl reabsorption by the thick ascending limb (TAL) is mediated by the NKCC2 cotransporter. Higher NKCC2 activity is involved in salt sensitive hypertension, and its phosphorylation is increased by fructose in rats. We hypothesized that high fructose (20% drinking water), would induce NKCC2 phosphorylation and induce salt sensitive hypertension in normal C57/Bl6J mice. To test this, mice were given 20% fructose in drinking water and after two weeks they were treated for 10 more weeks with either fructose alone or fructose plus 4% Na diet. Tail cuff systolic blood pressure (SBP) was measured after 3 weeks of training. Total NKCC2 expression, GAPDH and NKCC2 phosphorylation at Thre96/101 (P-NKCC2) were measured by Western blot in freshly isolated TALs. Baseline SBP was 112 ± 3 mmHg. A transient increase to 125± 4 mmHg ( p <0.05) was observed after 1 week on fructose which later decreased to 119 ± 3 mmHg ( p =0.14) by week 2. At the end of week 2, high salt chow was added. BP remained normal for 3 weeks and then increased to 137 ± 11 mmHg ( p <0.05) by week 4 on high salt, but not in fructose alone mice. After 10 weeks SBP remained elevated in the fructose plus high salt diet group (124 ± 3 vs 110 ± 5 mmHg; p <0.05). Water intake and urine volume was similar between the two high fructose groups. After 10 weeks, fasting glucose was higher in all mice with fructose (fructose + HS: 231± 8, fructose: 218 ± 7, normal diet: 122 ± 4 mg/dL, p <0.001). A fructose diet increased P-NKCC2 by 248 ± 82% (n=5, p <0.01) by one week and by 61 ± 21% ( p <0.05) at week 12. The combination of high-fructose high salt diet increased P-NKCC2 by 226 ± 75% ( p <0.05) at 12 weeks. Transcriptome profiling of isolated mouse TALs showed that 20% fructose (7 days) increased the expression of genes upstream of the SPAK and AMPK pathway. We conclude that 20% fructose in drinking water leads to a salt dependent increase in SBP, which appears to occur after mice develop abnormalities in glucose metabolism.