Abstract P284: Angiotensin II Upregulates Cytochrome-450 4A Expression in Rat Kidney Through Type 1 Receptor

Abstract

20-hydroxyeicosatetraenoic acids (20-HETE) is a cytochrome P-450 (CYP) 4A-dependent metabolite of arachidonic acid and regulates vascular tone and renal tubular function. Previous studies showed that angiotensin II (Ang II) stimulated the renal CYP activity and 20-HETE production through the Ang II type 1 (AT1) receptor and that the Ang II-increased the 20-HETE was linked to the Ang II type 2(AT2) receptor. Thus, the study was designed to clarify the role of Ang II in CYP4A isoforms expression in the rat kidney. Male Sprague-Dawley rats were infused Ang II at low dose (AL, 0.17mg/kg/min, sc) and high dose (AH, 0.70mg/kg/day, sc) by using osmotic mini pump, with or without AT1 receptor blocker candesartan (1 and 3mg/kg/day, po) for 1 week. The protein expression of CYP4A isoforms, AT1 receptor and AT2 receptor in the renal cortex, outer medulla, and inner medulla was examined by immunoblot analysis. The mRNA expression of CYP4A isoforms was examined by reverse transcription and polymerase chain reaction (RT-PCR). Ang II at high dose increased systolic blood pressure (control, 109±2; AH, 164±8 mmHg, p<0.01), creatinine (control, 0.24±0.00; AH, 0.29±0.01 mg/dl, p<0.01) and urinary albumin excretion (control, 20.3±5.9; AH, 2398.6±303.6 μg/mg creatinine, p<0.01). In the control group, the CYP4A1, 4A2, and 4A8 proteins were highly expressed in the renal cortex, lowly expressed in the outer medulla, barely detected in the inner medulla. The AT1 receptor was expressed in kidney sections; highly in the outer and inner medulla, the AT2 receptor was only detected in the outer medulla. Ang II dose-dependently increased all CYP4A isoform proteins in the renal cortex and outer medulla (CYP4A1, 24% and 222%; CYP4A2, by 51% and 258%; CYP4A8, by 52% and 550%, p<0.05). Ang II also increased all CYP4A isoform mRNAs in the renal cortex and outer medulla. The candesartan treatment dose-dependently inhibited the Ang II-increased blood pressure, creatinine, urinary albumin excretion and CYP4A isoform expressions. These results indicated that Ang II increases CYP4A isoform expressions in the kidney through AT1 receptor. The Ang II-upregulated CYP4A expressions may play an important role in hypertension and renal function.