Ang II Accumulation in Rat Renal Endosomes During Ang II-Induced Hypertension

Abstract

Abstract-Hypertension induced by long-term infusion of angiotensin II (Ang II) is associated with augmented intrarenalAng II levels to a greater extent than can be explained on the basis of the circulating Ang II levels. Although part of this augmentation is due to AT 1 receptor-dependent internalization, the intracellular compartments involved in this Ang II accumulation remain unknown. In the present study, we sought to determine whether Ang II trafficking into renal cortical endosomes is increased during Ang II hypertension, and if so, whether the AT 1 receptor antagonist, candesartan, prevents this accumulation. Compared with controls (nϭ12; 114Ϯ2 mm Hg), Ang II-infused rats (nϭ12; 80 ng/kg/min, SC, for 13 days) developed hypertension with systolic blood pressure rising to 185Ϯ4 mm Hg by Day 12. In Ang II hypertensive rats, plasma renin activity was suppressed, whereas plasma and kidney Ang II levels were increased by 3-fold (348Ϯ58 versus 119Ϯ16 fmol/mL) and 2-fold (399Ϯ39 versus 186Ϯ26 fmol/g). Intracellular endosomal Ang II levels were increased by more than 10-fold (1100Ϯ283 versus 71Ϯ12 fmol/mg protein), whereas intermicrovillar cleft Ang II levels were increased by more than 2-fold (88Ϯ22 versus 37Ϯ7 fmol/mg protein T he importance of angiotensin II (Ang II) in the development and maintenance of hypertension is well documented in several animal models of experimental hypertension, such as two-kidney, one-clip renal hypertension (2K1C), the Ren-2 gene transgenic rats, and the Ang IIinfused model. [1][2][3][4] The Ang II-dependent increases in arterial blood pressure are commonly associated with higher levels of circulating and intrarenal Ang II levels, structural abnormalities, and functional derangements in the kidney. [1][2][3][4][5][6] One important feature in the renin-angiotensin system profile observed in these rats is that renal Ang II levels are greater than can be explained on the basis of circulating Ang II and suppressed renin expression. 2,4,[7][8][9] This suggests that angiotensin peptides continue to be generated intrarenally via a renin-independent pathway, or that circulating Ang II accumulates in one or more compartments within the kidney. 4,9 Previous studies have shown that intrarenal Ang II levels are increased in the contralateral nonclip kidney of 2K1C hypertensive rats and in kidneys of Ang II-infused rats and Ren-2 transgenic rats. 2,4,[7][8][9] Because blockade of the AT 1 receptor with losartan normalizes blood pressure and prevents augmentation of intrarenal Ang II levels, this enhanced uptake of Ang II within the kidney appears to be mediated by the AT 1 receptor. 9,10 These results suggest that Ang II levels are augmented in intracellular compartments by an AT 1 receptormediated internalization mechanism and are protected from degradation to some extent.Recent studies have localized angiotensin peptides in renal endosomes and intermicrovillar clefts, thus implicating them as potential sites for intracellular accumulation in the kid-

AT 1 Receptor Mediated Augmentation of Intrarenal Angiotensinogen in Angiotensin II-Dependent Hypertension

“…Our present data extend these findings demonstrating that chronic ARB treatment blocks the increases in kidney cortex AGT protein levels and urinary excretion rates of AGT. Thus, ARB treatment antagonizes both the enhanced internalization of circulating Ang II into kidney cells [15][16][17] and the stimulation of intrarenal AGT expression, [11][12][13][14] resulting in the amelioration of the enhanced intrarenal Ang II contents seen during chronic Ang II infusion. ARB treatment also blocked the Ang II-mediated inhibition of renin release leading to increased circulating Ang II levels.…”

Renin-Angiotensin-Aldosterone System and Progression of Renal Disease

“…Intrarenal AngII is found regionally compartmentalized (24). Intact AngII is found in endosomes that are derived from receptor-mediated endocytosis.…”

Renal Renin-Angiotensin System

“…These results suggest that at least part of the augmented Ang II content in the kidney from Ang II-infused hypertensive rats is distributed to the RIF. Zhuo et al [59] showed that Ang II levels in renal cortical endosomes and intermicrovillar clefts are markedly increased in Ang II-infused hypertensive rats and that the increases in endosomal and intermicrovillar cleft Ang II levels were prevented by concurrent administration of candesartan. These results suggest that intracellular trafficking or accumulation of circulating and/or intrarenally formed Ang II into cortical tubular endosomes are enhanced during Ang II-dependent hypertension, and that this process is mediated by AT1 receptors.…”

“…Therefore, this pathway could also lead to de novo Ang II formation and secretion into the renal interstitial space. Treatment with AT1 receptor blockers prevents the cascade involving ligand-receptor activation and internalization [59] with subsequent stimulation of angiotensinogen synthesis and release [60], leading to reductions in RIF concentration of Ang II [56] (fig. 1d).…”