1. To investigate the mechanism by which sodium loading protects against acute renal failure we compared the effects of prior chronic loading with NaCl, or with NaHCO3, on renal function after injection of HgCl2.

2. Twenty-four male Sprague-Dawley rats were divided into three groups of eight rats. One group drank isotonic NaCl solution, a second drank isotonic NaHCO3 solution and the third control group drank deionized water. Acute renal failure was induced by HgCl2 on day 9, and the rats were killed 48 h after injection.

3. Net sodium balances and plasma volumes were similar in both groups of sodium-loaded rats. After HgCl2 serum creatinine was significantly less and urinary volume was greater in NaCl-loaded than in both NaHCO3-loaded and water-drinking animals.

4. Plasma renin activity of both NaCl- and NaHCO3-loaded animals was less than that of control rats. However, renal renin content was suppressed by NaCl but not by NaHCO3 loading.

5. Loading with NaCl afforded greater protection against HgCl2-induced acute renal failure than NaHCO3. Since this difference was not related to changes in sodium balance or plasma volume before HgCl2, or plasma renin activity after HgCl2, the results support the hypothesis that intrarenal renin plays a role in the pathogenesis of HgCl2-induced acute renal failure in the rat.

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