Lack of cardiac fibrosis in a new model of high prorenin hyperaldosteronism

Abstract

The aim of the present study was to test the hypothesis that elevation of prorenin in plasma is sufficient to induce cardiac fibrosis. Normotensive cyp1a1ren-2 transgenic rats with normal plasma prorenin and aldosterone levels were given 0.125% indole-3-carbinol (I3C) orally for a period of 12 wk. Plasma prorenin and aldosterone levels were determined in 4-wk intervals, and cardiac marker enzymes for hypertrophy, fibrosis, and oxidative stress as well as cardiac pathology were investigated. In I3C-treated cyp1a1 ren-2 transgenic rats, plasma prorenin concentrations were >100-fold elevated (> or = 7.1 + or - 2.6 microg ANG I.ml(-1).h(-1) vs. < or = 0.07 + or - 0.1; P < 0.001), whereas active renin levels were suppressed (0.09 + or - 0.02 vs. 0.2 + or - 0.1; P < 0.05). Aldosterone concentrations were elevated three- to fourfold for a period of >4 wk (574 + or - 51 vs. 160 + or - 68 pg/ml; P < 0.01). After 12 wk of I3C, rats exhibited moderate cardiac hypertrophy (heart weight/body weight 2.5 + or - 0.04 vs. 3.1 + or - 0.1 mg/g; P < 0.01). There was a slight increase in mRNA contents of endothelin 1 (1.21 + or - 0.08 vs. 0.75 + or - 0.007; P < 0.001), NADP oxidase-2 (1.03 + or - 0.006 vs. 0.76 + or - 0.04; P < 0.001), transforming growth factor-beta (0.99 + or - 0.06 vs. 0.84 + or - 0.04; P < 0.05), collagen type I (1.32 + or - 0.32 vs. 0.94 + or - 0.18; P < 0.05), and intercellular adhesion molecule-1 (1.12 + or - 0.12 vs. 0.84 + or - 0.08; P < 0.05). These genes are known to be stimulated by the renin-angiotensin system. There were no histological signs of fibrosis in the heart. We found that prorenin and aldosterone alone are not sufficient to induce considerable cardiac fibrosis in the absence of sodium load.

Fig. 1.

Plasma prorenin, active renin, and aldosterone concentrations in F344 control rats and cyp1a1ren-2 transgenic rats with and without indol-3-carbinol (I3C). P < 0.05 vs. day 0 (*) and vs. without I3C (+). #P < 0.01 vs. F344.

Fig. 2.

A: heart weight normalized to tibia length in F344 control rats and cyp1a1ren-2 transgenic rats (TGR) with and without I3C; n = 6 rats/group, *P < 0.01. B: left ventricular volume as determined by magnetic resonance imaging (MRI) analysis of formalin-fixed hearts of TGR with and without I3C; n = 6 rats/group. *P < 0.01.

Fig. 3.

MRI images of formalin-fixed hearts from cyp1a1ren-2 TGR without (A–C) and with (D–F) I3C. A and D: vertical long axis view. B and E: horizontal long axis view. C and F: long axis and midventricular short axis view. Arrows, mitral valve leaflets; star, aortic valve. Bar = 1 cm.

Fig. 4.

Azan-stained myocardial sections from cyp1a1ren-2 TGR without (left) and with (right) I3C. Bar = 100 μm.

Fig. 5.

Cardiac mRNA abundances of the (pro)renin receptor [(P)RR] marker genes for fibrosis [transforming growth factor-β (TGF-β), collagen type Ia1 (Col1a1), collagen type III (Col-3)] (A), hypertrophy [endothelin-1 (ET-1)], oxidative stress [NADP oxidase (NOX)-2, NOX-4], and inflammation [intercellular adhesion molecule-1 (ICAM-1)] (B) in F344 control rats and cyp1a1ren-2 TGR with and without I3C. The mRNA expression values were normalized to the geometric mean of the expression of porphobilinogen deaminase (PBGD) and β-actin mRNA; n = 6 rats/group. *P < 0.05 and **P < 0.01.

Fig. 6.

Western blot for extracellular signal-regulated kinase (ERK) 1/2 and phosphorylated Erk1/2 (p-ERK1/2) in rat vascular smooth muscle cells in the absence (none) or presence of rat or mouse ren-2 prorenin (1.6 ng/ml for 10 min). ANG II receptors were blocked with the angiotensin type 1 receptor blocker losartan and the angiotensin type 2 receptor blocker PD-123319 (30 min before and during stimulation) as indicated (solid line).