Abstract 343: EGF Deficiency in the Renal Cortex Contributes to Salt-sensitive Hypertension via Upregulation of ENaC Activity

Abstract

Dahl salt-sensitive (SS) rats fed a high salt diet exhibit increased blood pressure and renal damage. Epithelial sodium channels (ENaC) in the aldosterone-sensitive distal nephron (ASDN) are responsible for the fine tuning of Na + absorption in the kidney and are regulated by various stimuli including hormones and growth factors. Members of the epidermal growth factor (EGF) family are important for maintaining transepithelial Na + transport. A combination of electrophysiological, immunohistochemical, biochemical in vitro and chronic in vivo studies were used to provide mechanistic insights into ENaC regulation by EGF and how changes in this pathway may contribute to salt-induced hypertension in SS rats. It was found that the ENaC inhibitor benzamil, administered through the drinking water (15 mg/L), significantly reduced the MAP from 173.3±15.0 to 127.0±10.1 mm Hg. ENaC expression (as measured by Western blotting and immunohistochemistry) and activity (single channel analysis in freshly isolated split open ASDN) were significantly enhanced in SS rats fed a high salt diet compared to SS rats fed a low salt diet and consomic SS.13 BN rats fed a high salt chow. Servo-controlled measurements in SS rats also revealed increased ENaC expression in the uncontrolled kidneys compared to controlled left kidneys. As assessed by ELISA assay, EGF level in the kidney cortex of SS rats fed a high salt diet was lower compared to rats on a low salt diet. To directly evaluate the role of EGF in the development of hypertension and its effect on ENaC activity, EGF (10 μg/h/kg) was intravenously infused and blood pressure was continuously monitored. Chronic infusion of EGF decreased ENaC activity ( NP o ; from 1.5±0.2 to 0.4±0.1), prevented the development of hypertension (from 184.0±8.9 to 149.0±9.6 mm Hg) and attenuated renal glomerular and tubular damage. Thus, in controversy to existing dogma, we provide an evidence of a critical role of ENaC in the ASDN in the development of salt-sensitive hypertension. Furthermore, these findings indicate that EGF deficiency in the renal cortex contributes to salt-sensitive hypertension and that in vivo EGF infusion prevents development of hypertension and kidney damage via downregulation of ENaC.