Chronic blockade of NO synthase activity induces a proinflammatory phenotype in the arterial wall: prevention by angiotensin II antagonism

Chronic blockade of NO production induces hypertension and early occlusive and fibrotic end-stage organ damage owing to vascular lesions in the brain, kidney, and heart. In this study, we evaluated the inflammatory phenotypic changes induced in the arterial wall by chronic N(G)-nitro-L-arginine methyl ester (L-NAME) administration and the effect of an angiotensin II receptor (AT1) antagonist, irbesartan, on these changes. For this purpose, 2 groups of rats received L-NAME in the drinking water (50 mg x kg(-1) x d(-1)) for 2 months. One group received no other treatment and the other was treated with irbesartan (10 mg x kg(-1) x d(-1)). A third group (controls) received neither L-NAME nor irbesartan. After 8 weeks, plasma, aortas, and left ventricles were sampled from all 3 groups. Expression of inducible NO synthase (iNOS) was evaluated at both the mRNA (quantitative reverse transcription-polymerase chain reaction) and the protein (Western blot and immunohistochemistry) level in the aorta. Expression of intercellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1) was evaluated by reverse transcription-polymerase chain reaction, Western immunoblotting, and immunohistochemistry; inflammatory cell infiltration by immunohistochemistry; and fibrosis by Sirius red staining. Chronic L-NAME administration induced the expression of iNOS in the aorta, which was localized in smooth muscle cells as shown by immunohistochemistry and NADPH diaphorase activity. ICAM-1 and VCAM-1 expression was also increased in aortas of L-NAME-treated rats. These phenotypic changes of the vascular wall were associated with inflammatory cell infiltration and fibrosis in the heart. All of these pathological phenomena were prevented by the angiotensin II antagonist irbesartan. The proinflammatory phenotypic changes of the vascular wall induced by blockade of NOS activity could be involved in the interaction between endothelial dysfunction and the development of arteriosclerosis.

Remodelling of cardiac extracellular matrix during beta-adrenergic stimulation: upregulation of SPARC in the myocardium of adult rats

Our objectives were (i) to evaluate the expression of several genes involved in the remodelling of cardiac extracellular matrix (ECM), with a special interest on SPARC (secreted protein acidic and rich in cysteine) a glycoprotein with anti-adhesive properties, and (ii) to characterise structural changes in the left (LV) and right (RV) ventricles of rats subjected to continuous beta-adrenergic stimulation. The rats were infused for 3 or 7 days with isoproterenol (ISO, 4 mg/kg/day) or vehicle. Hybridisation analysis was done for SPARC, atrial natriuretic peptide (ANP),alpha2 (I) [COL-I] and alpha1 (III) [COL-III] procollagens, TGF-beta1 and TGF-beta3 mRNA content. Interstitial and perivascular collagen deposition in both ventricles was measured after specific staining. The mean cross-sectional area of LV cardiomyocytes was evaluated by quantitative histomorphometry. ISO provoked an increase of LV mass, and a progressive enlargement of cardiomyocytes: their cross-sectional area raised from 205+/-8 micrometer2 in vehicle-treated animals to 247+/-4 and 296+/-9 micrometer2 after 3 or 7 days of ISO infusion, respectively (P<0.001). SPARC messenger abundance increased by more than 50% in LV and RV, a first evidence of its expression in the myocardium of adult rats. Transcripts of ANP, COL-III, TGF-beta1 and TGF-beta3 increased in both ventricles. COL-I transcript increased in LV (75 and 116% on days 3 and 7), but not in RV. In LV, collagen accumulated in the interstitium (2.69+/-0.20v 9. 23+/-0.50% of tissue area for vehicle and ISO 7 days groups, P<0.05) and around coronary arteries (1.04+/-0.11v 4.47+/-0.48% of lumen area for vehicle and ISO 7 days,P<0.05). Cardiac fibrosis was less marked in RV. In conclusion, early expression of SPARC, an anti-adhesive protein, and preferential expression of COL-III, a distensible form of collagen, should increase ECM plasticity and facilitate ventricular remodelling.

Comparative efficacy of a DA2/alpha2 agonist and a beta-blocker in reducing adrenergic drive and cardiac fibrosis in an experimental model of left ventricular dysfunction after coronary artery occlusion

Attenuation of neuroendocrine activation may be beneficial in congestive heart failure. Sympathetic nervous system overactivity can be reduced by receptors blockade or by reducing norepinephrine (NE) spillover. This study evaluated and compared the effects of a DA2-dopaminergic receptor/alpha2-adrenoceptor agonist (CHF-1024) and a beta1-adrenoreceptor antagonist in terms of hemodynamics, ventricular remodeling, beta-adrenergic drive, and cardiac fibrosis after myocardial infarction (MI) in rats. MI was induced by left coronary artery ligation in 213 rats, whereas 12 were left unoperated on. After 2 months, the operated-on animals were treated for 1 more month with CHF-1024 at either 0.33 mg/kg/day (low dose) or 1 mg/kg/day (high dose) or with metoprolol (10 mg/kg/day), delivered through implanted osmotic minipumps. Plasma concentration and urinary excretion of NE were measured before the rats were killed. Hemodynamic variables were measured and morphometric analysis was done on the diastole-arrested hearts to quantify left ventricular remodeling and interstitial collagen density. Metoprolol treatment tended to normalize LV end-diastolic pressure (LVEDP). CHF-1024 at either dose, and metoprolol, significantly reduced collagen deposition in LV of infarcted animals (from 8.8 +/- 0.5% LV area in vehicle-treated rats to 6.6 +/- 0.2% or 6.4 +/- 0.2% after the low or high dose of CHF-1024, respectively; p < 0.05). Similarly, CHF-1024 at either dose reduced the plasma concentration of NE (from 224 +/- 53 pg/ml to 60 +/- 7 pg/ml or 87 +/- 13 pg/ml; p < 0.05) and urinary excretion of NE in rats with MI, whereas beta-blockade did not affect these variables. In conclusion, CHF-1024 infused for 1 month to rats with LV dysfunction reduced heart rate, NE spillover, and collagen deposition, without unwanted effects, only appearing at the higher dose. Effective beta-blockade with metoprotol reduced LVEDP with no effects on heart function. Neither DA2/alpha2 stimulation nor beta-blockade altered LV remodeling after coronary artery ligation.

Age-dependent expression of fibrosis-related genes and collagen deposition in the rat myocardium

OBJECTIVES

We sought to characterize the evolution, during maturational growth and early ageing, of the messenger abundance of four genes involved in cardiac fibrosis regulation (procollagens alpha2(I) and alpha1(III), transforming growth factors beta1, and beta3) and corroborate it with the alterations in collagen deposition in cardiac interstitium and around coronary arteries.

METHODS

Messenger RNA was quantified in LV and RV of 2-, 6-, 12- and 19-month-old male Sprague-Dawley rats (n = 5 per group) with Northern blot analysis. Collagen deposition was quantified with a semi-automated image analyser on Sirius red-stained sections of LV tissue.

RESULTS

There was an age-related monotonous decrease of procollagen type I (COL-I) transcript abundance in LV (p < 0.001) but not in RV. Procollagen type III (COL-III) expression decreased rapidly during maturational growth, both in LV and RV. On the other hand, collagen deposition in myocardial interstitium and around coronary arteries was slightly augmented during the maturational period of life (2-12 months), but with a higher rate during early ageing (up to 19 months). This was not accompanied by a significant thickening of the wall of coronary arteries. Transforming growth factor beta1, (TGF-beta1) and transforming growth factor beta3 (TGF-beta3) transcript abundance showed no major variations during ageing.

CONCLUSIONS

These results reflect a striking ventricular difference regarding the age-dependent expression of COL-I. The expression of TGF-beta(s), pleiotropic factors known to influence collagen pathway at different levels, does not seem to be profoundly altered during ageing. The discrepancy between protein and COL-I and COL-III mRNA levels indicates differences in age-related mRNA stability and/or regulation of collagen translation.

Changes in diastolic function and collagen content in normotensive and hypertensive rats with long-term streptozotocin-induced diabetes

We investigated the relationship between left ventricular diastolic function and interstitial collagen content in the endocardium, mesocardium and epicardium of transverse sections of the heart, using an image analysis system in normotensive and hypertensive long-term streptozotocin (STZ) diabetic rats. STZ-induced diabetes was characterised by elevated blood glucose, polyuria, polydypsia and loss of body weight. In vivo systolic blood pressure was 165 +/- 4, 136 +/- 3 and 129 +/- 7 mmHg in hypertensive and normotensive diabetic rats and age-matched controls, respectively. Heart rate was significantly lower (P < 0.01) in diabetic rats (283 +/- 8 and 280 +/- 10 beats min-1 in normotensive and hypertensive rats, respectively) than controls (393 +/- 18 beats min-1). Pressure-volume (P-V) curves were studied in isolated Langendorff perfused hearts at rest and after 20 min global ischaemia and 30 min reperfusion 6 months after induction of diabetes. Left ventricular volumes were significantly smaller in diabetic rats than age-matched controls, but volumes normalised for heart weight were higher in normotensive (by 28%) and hypertensive (by 10%) diabetic rats. Slopes of end-diastolic P-V curves were similar between groups in basal conditions, but left ventricular systolic P-V curves were steeper in normotensive and flatter in hypertensive diabetic hearts. Post-ischaemic left ventricular end-diastolic pressure was significantly higher than the pre-ischaemic value at comparable increments of volume in each group. Collagen content significantly increased in the heart of rats with STZ-diabetes both in the free left ventricular wall and septum, and suggested this may play a role in the cardiac defects in contractility and relaxation in our experimental conditions. These results indicate that diabetes, irrespective of associated hypertension, can cause major changes in cardiac performance and susceptibility to ischaemia and reperfusion.

A simple, automatic method for morphometric analysis of the left ventricle in rats with myocardial infarction

Induction of acute myocardial infarction in the rat is an established model for studying effects of therapeutic interventions. Images of sections of the rat left ventricle, stained with nitroblue tetrazolium, were digitized and several parameters estimated by dedicated software on an image analyzer (IBAS 2.0). The method was tested on 7 rats with 48-hr-old myocardial infarction and 4 sham-operated controls. Infarct size can be evaluated by two largely used methods, based on area or on angular extension of the lesion. Results of the two methods are linearly correlated, but area calculations give values half of those obtained from angular extension. Five minutes were needed for a complete evaluation of a section of the left ventricle. Estimates of the parameters showed a relatively low between- and within-operator variability and a good correlation with a classic, but time-consuming, planimetric method. The method simultaneously measures infarct size and left ventricular geometry in the rat. The advantages over previous nonautomatic methods are simplicity, good reproducibility, and speed of execution, which make it particularly useful in the evaluation of drug effects.