Renal Hemodynamics and Plasma and Kidney Angiotensin II in Established Diabetes Mellitus in Rats: Effect of Sodium and Salt Restriction

Six weeks after the onset of insulin-treated streptozotocin diabetes (STZ) in Munich-Wistar rats, the effect of a low-sodium (LNa) and a low-salt (LNaCl) diet on renal function and on plasma and kidney tissue angiotensin II (AIIp, AIIk) was tested. Clearance experiments were performed in anesthetized rats 7 days after starting on LNa or LNaCl. On a control diet, STZ exhibited an increase in GFR, RBF, and kidney weight (KW) and a reduction in renal vascular resistance (RVR) and AIIk, but no change in AIIp, compared with nondiabetic normal rats (CON). Although sodium restriction reduced and salt restriction increased AIIk in CON, both diets increased AIIp without affecting renal hemodynamics or KW. In diabetic rats, both salt and sodium restriction further increased GFR and RBF by reducing RVR, increased KW, and changed AIIk and AIIp in a similar pattern, but at significantly lower values compared with CON. Daily treatment of STZ-LNa with the AII-receptor blocker losartan (20 mg/L, in drinking water) did not affect the reduction in RVR and the increase in KW but slightly reduced RBF because of a decrease in mean arterial blood pressure and further increased GFR. It was concluded that (1) AIIk but not AIIp is affected differently by LNa compared with LNaCl in both CON and STZ; (2) LNaCl and LNa change AIIp and AIIk in a similar pattern but at significant lower values in STZ compared with CON; and (3) with regard to renal hemodynamics and KW, the response to LNa and LNaCl is different in CON compared with rats 6 wk after the onset of diabetes mellitus, the latter exhibiting a further increase in renal hyperfiltration and KW by a mechanism that is not directly AII receptor dependent.