It has been shown that chronic CsA treatment is associated with increased expression of an acidic renin isoform and the development of arteriolopathy in rat kidney. Since dietary sodium restriction enhances these effects, it is hypothesized that renal renin enzymatic activity also will be changed by these conditions. Male Sprague Dawley rats received a LS diet for 3 (n=4) or 5 (n=4) weeks. In addition, an equal number of rats in each group received CsA 25 mg/kg/d orally, a dose known to cause renal toxicity. Kidneys were removed and homogenized. Renin enzymatic activity was measured for 1 hr at 37°C in rat kidney homogenate at pH 6.2, the optimum pH, and pH 5.2. Angiotensin I assayed by RIA indicated renin enzymatic activity in the samples. Data are expressed as ng AI/ mg protein/hr. Table