Genetic Clamping of Renin Gene Expression Induces Hypertension and Elevation of Intrarenal Ang II Levels of Graded Severity in Cyp1a1-Ren2 Transgenic Rats

Abstract

Introduction. Transgenic rats with inducible angiotensin II (Ang II)-dependent hypertension (strain name: TGR[Cyp1a1-Ren2]) were generated by inserting the mouse Ren2 renin gene, fused to the cytochrome P450 1a1 (Cyp1a1) promoter, into the genome of the rat. The present study was performed to characterise the changes in plasma and kidney tissue Ang II levels and in renal haemodynamic function in Cyp1a1-Ren2 rats following induction of either slowly developing or malignant hypertension in these transgenic rats. Materials and Methods. Arterial blood pressure (BP) and renal haemodynamics and excretory function were measured in pentobarbital sodium-anaesthetised Cyp1a1-Ren2 rats fed a normal diet containing either a low dose (0.15%, w/w for 14-15 days) or high dose (0.3%, w/w for 11-12 days) of the aryl hydrocarbon indole-3-carbinol (I3C) to induce slowly developing and malignant hypertension, respectively. In parallel experiments, arterial blood samples and kidneys were harvested for measurement of Ang II levels by radioimmunoassay. Results. Dietary I3C increased plasma renin activity (PRA), plasma Ang II levels, and arterial BP in a dose-dependent manner. Induction of different fixed levels of renin gene expression and PRA produced hypertensive phenotypes of varying severity with rats developing either mild or malignant forms of hypertensive disease. Administration of I3C, at a dose of 0.15% (w/w), induced a slowly developing form of hypertension whereas administration of a higher dose (0.3%) induced a more rapidly developing hypertension and the clinical manifestations of malignant hypertension including severe weight loss. Both hypertensive phenotypes were characterised by reduced renal plasma flow, increased filtration fraction, elevated PRA, and increased plasma and intrarenal Ang II levels. These I3C-induced changes in renal haemodynamics, PRA and kidney Ang II levels were more pronounced in Cyp1a1-Ren2 rats with malignant hypertension. Chronic administration of the AT 1 -receptor antagonist,

Mechanism underlying the efficacy of combination therapy with losartan and hydrochlorothiazide in rats with salt-sensitive hypertension

“…Plasma angiotensin II concentration was determined by radioimmunoassay as described previously. 26,27 Plasma aldosterone concentration was measured by radioimmunoassay with the use of a DPC aldosterone kit (Mitsubishi Chemical Medience, Tokyo, Japan). The plasma concentration of nitric oxide metabolites (NO x ) was determined by the Griess method with the use of a Nitrate/Nitrite Colorimetric Assay Kit (Cayman Chemical, Ann Arbor, MI, USA), as previously described.…”

Cardiac remodeling and diastolic dysfunction in DahlS.Z-Leprfa/Leprfa rats: a new animal model of metabolic syndrome

“…Plasma renin activity was determined by radioimmunoassay with the use of renin RIA beads (Abbott Japan, Tokyo, Japan). Plasma angiotensin II (Ang II) concentration was determined by radioimmunoassay as described previously, 14,15 and serum aldosterone concentration was measured by radioimmunoassay with the use of a DPC aldosterone kit (Mitsubishi Chemical Medience, Tokyo, Japan). Extended details appear in the Supplementary Material online.…”

Renal vascular and tubulointerstitial inflammation and proliferation in Cyp1a1-Ren2 transgenic rats with inducible ANG II-dependent malignant hypertension

“…We have demonstrated that at a dose of 0.3% (wt/wt), chronic dietary administration of I3C induces malignant hypertension in Cyp1a1-Ren2 transgenic rats (27,28,31,32). Malignant hypertension is a severe form of hypertension characterized by rapidly increasing blood pressure, pressure diuresis and natriuresis, severe renal vasoconstriction and ischemia, activation of the renin-angiotensin system, microangiopathy, hemolytic anemia, and development of retinopathy (23,47,48).…”

“…In essence, induction of the Cyp1a1 promoter by I3C is used to drive hepatic expression of the Ren2 renin gene. In this transgenic rat model, induction of the Cyp1a1 promoter by dietary administration of I3C results in a fixed level of expression the Ren2 renin gene and in the development of ANG II-dependent hypertension (23,27). This transgenic rat model, therefore, allows genetic clamping of extrarenal renin gene expression and induction of ANG IIdependent malignant hypertension consequent to fixed levels of elevated plasma renin that are not subject to normal homeostatic regulation (27).…”

“…Accordingly, this model allows induction of ANG II-dependent hypertension of graded severity using a benign and naturally occurring dietary supplement without the need for surgical intervention, dietary salt manipulation, or the administration of steroids (23,27). In essence, the Cyp1a1-Ren2 transgenic rat model is particularly advantageous because of the ease and reproducibility of genetically clamping expression of the Ren2 gene and inducing increases in plasma renin activity, plasma and intrarenal ANG II levels, and hypertension of graded severity (22,27,28,31,32).We have demonstrated that at a dose of 0.3% (wt/wt), chronic dietary administration of I3C induces malignant hypertension in Cyp1a1-Ren2 transgenic rats (27,28,31,32). Malignant hypertension is a severe form of hypertension characterized by rapidly increasing blood pressure, pressure diuresis and natriuresis, severe renal vasoconstriction and ischemia, activation of the renin-angiotensin system, microangiopathy, hemolytic anemia, and development of retinopathy (23,47,48).…”