Differential development of early hypertension in heterozygous transgenic TGR(mREN2)27 rats

Intrapulmonary Activation of the Angiotensin-Converting Enzyme Type 2/Angiotensin 1-7/G-Protein-Coupled Mas Receptor Axis Attenuates Pulmonary Hypertension in Ren-2 Transgenic Rats Exposed to Chronic Hypoxia

The present study was performed to evaluate the role of intrapulmonary activity of the two axes of the renin-angiotensin system (RAS): vasoconstrictor angiotensin-converting enzyme (ACE)/angiotensin II (ANG II)/ANG II type 1 receptor (AT1) axis, and vasodilator ACE type 2 (ACE2)/angiotensin 1-7 (ANG 1-7)/Mas receptor axis, in the development of hypoxic pulmonary hypertension in Ren-2 transgenic rats (TGR). Transgene-negative Hannover Sprague-Dawley (HanSD) rats served as controls. Both TGR and HanSD rats responded to two weeks´ exposure to hypoxia with a significant increase in mean pulmonary arterial pressure (MPAP), however, the increase was much less pronounced in the former. The attenuation of hypoxic pulmonary hypertension in TGR as compared to HanSD rats was associated with inhibition of ACE gene expression and activity, inhibition of AT1 receptor gene expression and suppression of ANG II levels in lung tissue. Simultaneously, there was an increase in lung ACE2 gene expression and activity and, in particular, ANG 1-7 concentrations and Mas receptor gene expression. We propose that a combination of suppression of ACE/ANG II/AT1 receptor axis and activation of ACE2/ANG 1-7/Mas receptor axis of the RAS in the lung tissue is the main mechanism explaining attenuation of hypoxic pulmonary hypertension in TGR as compared with HanSD rats.

Relaxin ameliorates fibrosis in experimental diabetic cardiomyopathy

Fibrosis (extracellular matrix accumulation) is the final end point in diabetic cardiomyopathy. The current study evaluated the therapeutic effects of the antifibrotic hormone relaxin (RLX) in streptozotocin-treated transgenic mRen-2 rats, which undergo pathological and functional features similar to human diabetes. Twelve-week-old hyperglycemic mRen-2 rats, normoglycemic control rats, and animals treated with recombinant human gene-2 (H2) RLX from wk 10-12 were assessed for various measures of left ventricular (LV) fibrosis, hemodynamics, and function, while the mechanism of RLX's actions was also determined. Hyperglycemic mRen-2 rats had increased LV collagen concentration (fibrosis) and gelatinase activity (all P < 0.05 vs. controls) but equivalent levels of interstitial collagenase and tissue inhibitor of metalloproteinase-1 to that measured in control rats. The increased LV fibrosis associated with diabetic animals led to significant alterations in the E/A wave ratio and E-wave deceleration time (both P < 0.05 vs. controls) in the absence of blood pressure changes, reflective of myocardial stiffness and LV diastolic dysfunction. H2-RLX treatment of diabetic rats led to significant decreases in interstitial and total LV collagen deposition (both P < 0.05 vs. diabetic group), resulting in decreased myocardial stiffness and improved LV diastolic function, without affecting nondiabetic animals. The protective effects of H2-RLX in diabetic rats were associated with a reduction in mesenchymal cell differentiation and tissue inhibitor of metalloproteinase-1 expression in addition to a promotion of extracellular matrix-degrading matrix metalloproteinase-13 (all P < 0.05 vs. diabetic group) but were independent of blood pressure regulation. These findings demonstrate that RLX is an antifibrotic with rapid-occurring efficacy and may represent a novel therapy for the treatment of diabetes.

Effects of Dietary Salt Load and Salt Depletion on the Course of Hypertension and Angiotensin II Levels in Male and Female Heterozygous Ren-2 Transgenic Rats

BACKGROUND

In the present study we evaluated plasma and kidney angiotensin II (ANG II) levels in female and male Ren-2 transgenic rats (TGR) in comparison to age-matched female and male normotensive Hannover Sprague-Dawley rats.

METHODS

The rats were maintained on a normal sodium (NS) diet (0.6% NaCl) or fed a high sodium (HS) diet (2% NaCl) for 4 days or were sodium depleted by administration of 40 mg furosemide per liter drinking water overnight followed by 3 days of low sodium diet (0.01% NaCl) (LS + F). ANG II levels were determined by radioimmunoassay.

RESULTS

Female TGR at the age of 38 days were already hypertensive and had developed cardiac hypertrophy, whereas male TGR at this age still exhibited a normotensive phenotype. HS diet increased the blood pressure (BP) but did not alter the ANG II levels in TGR at any age. LS + F decreased the BP without significant change in ANG II concentrations in TGR. Female TGR responded to salt loading and salt depletion by more pronounced changes in BP than male TGR.

CONCLUSIONS

Female TGR develop hypertension more rapidly and the salt-sensitive component of hypertension is more pronounced in female than in male TGR.

Differential expression of nuclear AT1 receptors and angiotensin II within the kidney of the male congenic mRen2. Lewis rat

We established a new congenic model of hypertension, the mRen(2). Lewis rat and assessed the intracellular expression of angiotensin peptides and receptors in the kidney. The congenic strain was established from the backcross of the (mRen2)27 transgenic rat that expresses the mouse renin 2 gene onto the Lewis strain. The 20-wk-old male congenic rats were markedly hypertensive compared with the Lewis controls (systolic blood pressure: 195 +/- 2 vs. 107 +/- 2 mmHg, P < 0.01). Although plasma ANG II levels were not different between strains, circulating levels of ANG-(1-7) were 270% higher and ANG I concentrations were 40% lower in the mRen2. Lewis rats. In contrast, both cortical (CORT) and medullary (MED) ANG II concentrations were 60% higher in the mRen2. Lewis rats, whereas tissue ANG I was 66 and 84% lower in CORT and MED. For both strains, MED ANG II, ANG I, and ANG-(1-7) were significantly higher than CORT levels. Intracellular ANG II binding distinguished nuclear (NUC) and plasma membrane (PM) receptor using the ANG II radioligand 125I-sarthran. Isolated CORT nuclei exhibited a high density (Bmax >200 fmol/mg protein) and affinity for the sarthran ligand (KD<0.5 nM); the majority of these sites (>95%) were the AT1 receptor subtype. CORT ANG II receptor Bmax and KD values in nuclei were 75 and 50% lower, respectively, for the mRen2. Lewis vs. the Lewis rats. In the MED, the PM receptor density (Lewis: 50 +/- 4 vs. mRen2. Lewis: 21 +/- 5 fmol/mg protein) and affinity (Lewis: 0.31 +/- 0.1 vs. 0.69 +/- 0.1 nM) were lower in the mRen2. Lewis rats. In summary, the hypertensive mRen2. Lewis rats exhibit higher ANG II in both CORT and MED regions of the kidney. Evaluation of intracellular ANG II receptors revealed lower CORT NUC and MED PM AT1 sites in the mRen2. Lewis. The downregulation of AT1 sites in the mRen2. Lewis rats may reflect a compensatory response to dampen the elevated levels of intrarenal ANG II.