EFFECTS OF CHRONIC, UREA-INDUCED OSMOTIC DIURESIS ON KIDNEY WEIGHT AND FUNCTION IN RATS

To study the effects of chronic osmotic diuresis which were not associated with hyperglycaemia on the rat kidney, osmotic diuresis was induced by i.v. infusion of urea. A 5 mol/l urea solution was continuously infused at a rate of 100 ml.kg(-1) day(-1) on the basis of body weight on day 0. Duration of infusion was 2, 6,10 or 14 days. Control rats received continuously infused Ringer's solution. Urea-treated groups developed osmotic diuresis (urine flow = about 0.04 ml.min(-1).100 g body weight(-1)) comparable to that in rats with experimental diabetes mellitus induced by i.v. streptozotocin (55 mg/kg), however urea-induced osmotic diuresis was not associated with blood glucose level:increases. Compared with their controls, rats receiving urea for 2-14 days had markedly increased kidney weight. Rats receiving urea for 10 days showed greatest kidney weight increase, 0.565 +/- 0.044 g/100 g body weight (mean +/- SD),representing a 53 % increase compared with the control (0.369 +/- 0.034 g/100 g body weight). Kidney weight was associated with increases in kidney protein content. In contrast, none of control kidney weight values differed significantly from day 0 values (=normal rats; 0.387 +/- 0.028 g/100g body weight). Creatinine clearance values in urea-treated groups were also higher than those in controls. The maximum value, 0.65 +/- 0.17.ml.min(-1).100 g body weight(-1), was recorded in the 14-day group and was significantly higher than the corresponding control value (0.34 +/- 0.07 ml.min(-1).100 g body weight(-1)) (p < 0.001). Urea clearance values were also significantly higher in urea-treated groups than in respective controls. This study suggests that osmotic diuresis may induce renal hypertrophy/hyperplasia and glomerular hyperfiltration immediately after development of diabetes.