Autoregulation of renal blood flow (RBF) was studied in male Wistar rats. We studied 11 control rats, 11 rats with severe streptozocin (STZ)-induced hyperglycemia (diabetic group), and 10 moderately hyperglycemie rats made diabetic by injection of STZ but given 2–8 U s.c. insulin daily (insulin-treated group). RBF was measured by an electromagnetic flowmeter during stepwise reduction of renal perfusion pressure 4–8 wk after injection of STZ (older group). RBF autoregulation of the diabetic group was impaired compared with the control group. In the insulin-treated group, autoregulatory capability was less attenuated than in the diabetic group. The average autoregulatory index (ARI) of the diabetic group (0.61 ± 0.05) was greater than that of the control (0.24 ± 0.02, P < .01) and the insulin-treated (0.33 ± 0.07, P < .05) groups. To study the relationship between autoregulation and the duration of diabetes, an autoregulatory study was also made in a group of 22 rats (11 diabetic and 11 control) that were tested 2–3 wk after injection of STZ (younger group). The ARI in the younger diabetic group was smaller than that in the older diabetic group (P < .05). The results suggest that in uncontrolled diabetes RBF fluctuates with blood pressure change, and protection against hypertensive injury of glomerular capillaries may be diminished. Autoregulatory disability develops with time, and insulin treatment diminishes impairment of autoregulation. These findings may also explain the adverse consequences of hypertension on the progression of diabetic nephropathy in poorly controlled diabetes.

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