BACKGROUND: Diabetic nephropathy is characterized by glomerular and tubular hypertrophy, and angiotensin II receptor blockers (ARBs) are known to prevent renal hypertrophy in diabetic patients. METHODS: To determine the effect of ARB on podocyte p27(Kip1) mRNA and protein expression, podocytes were exposed to 5.6 mmol/L normal glucose or 25 mmol/L high glucose with or without ARB, 10(-7) mol/L L-158,809. For animal studies, streptozotocin-induced diabetic rats were left untreated or were treated with 1 mg/kg/day L-158,809 for 3 months (diabetes mellitus + ARB). Competitive reverse transcription-polymerase chain reaction (RT-PCR), Western blot, immunohistochemistry, and morphometric analyses were performed. RESULTS: p27(Kip1) mRNA and protein expression in podocytes exposed to high glucose and in 3-month diabetic glomeruli were significantly increased (P < 0.01). High glucose significantly increased angiotensin II levels both in cell lysates and in media compared with normal glucose (P < 0.05) and exogenous angiotensin II also increased p27(Kip1) mRNA and protein expression in podocytes. L-158,809 treatment in podocytes inhibited the increase in p27(Kip1) mRNA expression by 84%, and protein expression by 89% (P < 0.05). p27(Kip1) mRNA and protein expression in diabetic + ARB glomeruli were also significantly reduced by 78% and 85%, respectively, compared with diabetic glomeruli (P < 0.01). ARB treatment also significantly ameliorated increased glomerular p27(Kip1) expression in diabetes mellitus as assessed by immunohistochemistry (P < 0.01). The increase in glomerular volume in diabetes mellitus was also inhibited by 81% with ARB treatment (P < 0.05). CONCLUSION: p27(Kip1) mRNA and protein expression were increased in diabetic glomeruli as well as in high glucose-stimulated podocytes, and this increment in p27(Kip1) expression was ameliorated by ARB treatment. These findings indicate that ARB treatment has an additional effect on preventing renal hypertrophy in diabetes mellitus.