EFFECTS OF DIABETES AND INSULIN ON EXPRESSION OF KALLIKREIN AND RENIN GENES IN THE KIDNEY

We previously showed that renal prokallikrein synthesis is reduced in streptozotocin (STZ)-diabetic rats. Plasma renin activity is also reduced in diabetic rats. To investigate the molecular mechanisms underlying these changes, we examined the effects of diabetes and insulin treatment on renal kallikrein and renal renin mRNA levels and the activities of these enzymes. Rats made diabetic by STZ were either treated with 1.5 to 1.75 U PZI insulin daily to maintain moderate hyperglycemia (plasma glucose 200 to 300 mg/dl, D + I) or left untreated to produce severe hyperglycemia (plasma glucose > 400 mg/dl, D). Control (C) rats were also studied. After three weeks, renal kallikrein mRNA was reduced 50% in D rats. A proportional reduction in immunoreactive kallikrein was also observed (37.8 +/- 2.5 vs. 55.8 +/- 6.8 ng/mg protein, D vs. C, P < 0.001). Kallikrein mRNA and immunoreactive kallikrein levels in D + I rats were not different from C rats. Renin mRNA level was also markedly reduced in D rats, compared to C rats. This was associated with reduced plasma renin concentration (4.5 +/- 0.2 vs. 10.5 +/- 1.6 ng Ang I/ml/hr, D vs. C, P < 0.01). However, renal renin concentration was unchanged (0.84 +/- 0.17 vs. 0.84 +/- 1.3-mu-g Ang I/mg protein/hr, D vs. C). In D + I rats, renin mRNA level and plasma renin concentration were not different from C levels. However, renal renin concentration was increased (1.49 +/- 0.27-mu-g Ang I/mg protein/hr) compared to C rats (P < 0.05). beta-actin mRNA levels were unchanged in either diabetic rat group. These data show that the diabetic state suppresses kallikrein and renin mRNA levels. Insulin treatment reverses the reductions in message levels and results in normal or increased tissue enzyme activities.