Objectives: Beneficial effects of angiotensin II type 1 receptor blockers have been indicated for patients with diabetic nephropathy. We investigated the effects of an angiotensin II type 1 receptor blocker, telmisartan, on intrarenal angiotensin II levels and the progression of albuminuria or glomerular injury in type 2 diabetic Otsuka Long-Evans Tokushima Fatty rats with microalbuminuria.
Methods and results: Otsuka Long-Evans Tokushima Fatty rats were randomly treated with telmisartan (10 mg/kg/day, orally), hydralazine (25 mg/kg/day in drinking water) or vehicle from the initiation of albuminuria (13 weeks old). At this age, Otsuka Long-Evans Tokushima Fatty rats showed low but detectable albuminuria (1.0 +/- 0.1 mg/day) and higher systolic blood pressure, postprandial blood glucose and kidney angiotensin II levels than age-matched nondiabetic Long-Evans Tokushima Otsuka rats. At 35 weeks of age, vehicle-treated Otsuka Long-Evans Tokushima Fatty rats did not show apparent glomerular injury or tubulointerstitial fibrosis but did exhibit severe albuminuria (72.6 +/- 5.9 mg/day) and accumulation of cytoplasmic granules containing albumin in podocytes. Otsuka Long-Evans Tokushima Fatty rats also showed higher systolic blood pressure, postprandial blood glucose, collagen gene expression, desmin staining (a marker of podocyte injury) and angiotensin II levels than Long-Evans Tokushima Otsuka rats. Treatment with telmisartan did not affect postprandial blood glucose but decreased systolic blood pressure, collagen gene expression, desmin staining and angiotensin II levels. Telmisartan also prevented the development of albuminuria (0.6 +/- 0.1 mg/day at 35 weeks old) and accumulation of cytoplasmic granules. Hydralazine treatment resulted in a similar reduction in systolic blood pressure and partially attenuated the albuminuria (35.4 +/- 1.8 mg/day at 35 weeks old) but did not affect the other parameters.
Conclusion: The present results suggest the contribution of augmented intrarenal angiotensin II levels to the initiation and progression of albuminuria as well as podocyte abnormalities in type 2 diabetic rats. Angiotensin II blockade may inhibit the transition from microalbuminuria to overt nephropathy through prevention of intrarenal angiotensin II augmentation, independently of changes in blood pressure and glucose levels.