Renal expression of angiotensin receptors in long-term diabetes and the effects of angiotensin type 1 receptor blockade

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Abstract
The aims of this study were to assess the renal expression of angiotensin type 1 (AT1) and type 2 (AT2) receptors in diabetic spontaneously hypertensive rats (SHR) and the effect of AT1 receptor blockade on the expression of these receptors. Diabetes was induced by injection of streptozotocin in SHRs. Irbesartan, an AT1 receptor antagonist, was given to diabetic SHRs for 32 weeks (15 mg/kg per day, n = 10). Diabetic (n = 10) and non-diabetic SHRs (n = 10) were studied concurrently. A separate group of control and diabetic Wistar–Kyoto (WKY) rats were also evaluated. Gene and protein expressions of the AT1 and AT2 receptor were assessed by reverse transcription-polymerase chain reaction (RT-PCR), immunohistochemistry with specific antibodies and in vitro autoradiography with [125I]Sar(1), Ile(8) angiotensin II or [125I]CGP42112B. Both AT1 and AT2 receptor mRNA levels in the kidney were reduced in diabetic SHRs compared to non-diabetic SHRs. Immunohistochemistry staining with specific antibodies showed a similar reduction in glomerular and tubulo-interstitial staining for both AT1 and AT2 receptors. Reduced binding for the AT1 and AT2 receptor was found in the kidney of diabetic SHRs. Diabetic SHRs developed albuminuria and had glomerular and tubulo-interstitial injury, which were prevented by treatment with irbesartan. Reduced expression of the AT1 receptor, but not the AT2 receptor, in diabetic SHRs was prevented by treatment with irbesartan. In diabetic WKY rats no such reduction in AT1 expression was observed, although there was a trend for reduced AT2 receptor expression. These findings demonstrated that renal expression of both AT1 and AT2 receptor was reduced in long-term diabetic SHRs and that blockade of the AT1 receptor had disparate effects on expression of angiotensin II receptor subtypes.