Effects of dietary salt and potassium intervention on TGF-β1 expression and fibrosis in renal medulla of Dahl salt-sensitive rats

Objective: To investigate the effects of high sodium and supplementary potassium intake on blood pressure, transforming growth factor (TGF-β1) expression and fibrosis of renal medulla of Dahl salt-sensitive rats so as to explore the effects of TGF-β1 on the occurrence of salt-sensitive hypertension and target organ damage. Methods: We divided 24 six-week-old male Dahl salt-sensitive rats and 24 SS-13BN rats randomly into low salt group, high salt group, and high salt plus high potassium group, which were given 4 g/kg NaCl, 80 /kg NaCl and 80 g/kg NaCl + 80 g/kg KCl diets, respectively, for four weeks. Their tail blood pressure was measured before and after the diet intervention. TGF-β1 expression in renal medulla was assessed by reverse transcription-PCR and immunohistochemical staining; the development of fibrosis in renal medulla was observed through Masson staining. Results: After 4 weeks' diet intervention, in Dahl salt-sensitive rats, blood pressure increased significantly in high salt group compared with that in low salt group [(169.9±2.2)mmHg vs. (147.1±6.1)mmHg, P<0.01], that of the high salt plus potassium group was evidently decreased compared with that of high salt group (123.6±3.8 mmHg vs. 169.9±2.2 mmHg, P<0.01). In SS-13BN rats, blood pressure increased in high salt group compared with that in low salt group [(145.6±1.9)mmHg vs. (140.2±3.7)mmHg, P<0.05]; that of high salt plus potassium group was decreased compared with that of high salt group [(125.2±2.8)mmHg vs. (145.6±1.9)mmHg, P<0.01]. The mRNA and protein expressions of TGF-β1 in renal medulla of high salt group increased significantly compared with those of low salt group among Dahl salt-sensitive rats (0.87±0.02 vs. 0.67±0.04, P<0.01; 0.136±0.002 vs. 0.030±0.002, P<0.01), and that of high salt plus potassium group decreased significantly compared with that of high salt group (0.55±0.04 vs. 0.87±0.02, P<0.01; 0.070±0.008 vs. 0.136±0.002, P<0.01). In Dahl salt-sensitive rats, there was more collagen deposition in renal tubular area in high salt group than in low salt group (0.075±0.002 vs. 0.037±0.002, P<0.01). and that of the high salt plus potassium group decreased significantly compared with that of high salt group (0.038±0.008 vs. 0.075±0.002, P<0.01). Conclusion: High-salt diet can cause significant rise in blood pressure and TGF-β1 expression, and lead to fibrosis of renal medulla in Dahl salt-sensitive rats. Supplementation of potassium can alleviate blood pressure increase caused by high-salt diet and protect the target organs.