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.

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.

Effects of a new angiotensin-converting enzyme inhibitor (idrapril) in rats with left ventricular dysfunction after myocardial infarction.

We evaluated the effects of a new angiotensin-converting enzyme (ACE) inhibitor (idrapril) in terms of hemodynamics and ventricular remodeling after myocardial infarction in rats. The animals were randomly assigned to four experimental groups. Myocardial infarction was induced by left coronary artery ligation in the first two groups treated with either idrapril (300 mg kg-1 day-1) or vehicle for 4 weeks after myocardial infarction. Two groups of sham-operated rats were treated accordingly. Hemodynamics were measured, and the diastole-arrested hearts were analyzed morphometrically to quantify left ventricular (LV) remodeling and infarct size. In infarcted rats, idrapril reduced the arterial systolic blood pressure (SBP) from 128 +/- 10 to 97 +/- 6 mm Hg (p < 0.05) and LV end-diastolic pressure (LVEDP) from 19 +/- 3 to 13 +/- 3 mm Hg (p < 0.01). The decrease in diastolic wall stress conferred by idrapril to infarcted rats (from 499 +/- 99 to 269 +/- 68 dynes mm-2, p < 0.05) was mainly due to a reduction in LVEDP and, to a lesser extent, in LV volume. Idrapril also reduced body and heart weights as compared with those of vehicle-treated animals. Four-week treatment with idrapril initiated immediately after myocardial infarction reduced LVEDP and limited LV wall stress, a major prognostic factor for the progression toward chronic ventricular failure.

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.