Increased renal production of angiotensin II and thromboxane B2 in conscious diabetic rats.

The mechanisms involved in development of cardiovascular complications associated with diabetes mellitus are not well elucidated. Among the vasoactive factors that may play a role in development of these complications are angiotensin II and thromboxane B2 (TXB2). We hypothesized that diabetes increases renal production of TXB2 through stimulation of angiotensin type-1 receptor. We used a microdialysis technique to monitor changes in renal interstitial fluid (RIF) TXB2 in conscious streptozotocin-induced diabetes rat model. The RIF levels of angiotensin II and TXB2 were monitored before and during 6 weeks after development of diabetes and during treatment with the angiotensin type-1 receptor blocker valsartan at 10 mg/kg. Measurement of the urinary albumin excretion (UAE) was used to monitor the development and progression of diabetic nephropathy. The UAE was 81.62 +/- 1.31 ng/min, 184.75 +/- 9.41 ng/min (P < .01), and 229.84 +/- 4.49 ng/min (P < .0001) at baseline, week 3, and week 6, respectively, after induction of diabetes. Basal levels of RIF angiotensin II were 4.28 +/- 0.02 pg/mL and significantly increased to 6.24 +/- 0.31 pg/mL (P < .001) and 7.66 +/- 0.05 pg/mL (P < .001) at 3 and 6 weeks after development of diabetes. Similarly, basal RIF TXB2 was 197 +/- 27 pg/mL and increased to 488 +/- 80 pg/mL (P < .01) and 703 +/- 130 pg/mL (P < .01) at 3 and 6 weeks after development of diabetes. Valsartan caused further increase in RIF angiotensin II levels. In contrast, valsartan decreased RIF TXB2 levels at baseline to 85 +/- 11 pg/mL (P < .01), at 3 weeks to 141 +/- 17 pg/mL (P < .01), and at 6 weeks to 255 +/- 45 pg/mL (P < .01) after development of diabetes. These results demonstrate that diabetes mellitus is accompanied by increased renal production of angiotensin II and TXB2. The increase in TXB2 is mediated through stimulation of angiotensin type-1 receptor.