Electrocardiographic changes in cardiomyopathic Syrian hamsters (strain BIO 8262)

Effects of beta-adrenoceptor blockade on beta-adrenergic signal transduction in cardiomyopathic hamster (BIO 8262) hearts

In myopathic BIO 8262-hamsters beta1-adrenergic stimulation of cardiac adenylyl cyclase has been found to be markedly reduced compared to that of healthy controls. In order to test the hypothesis that the functional uncoupling of beta1-adrenoceptors in diseased hamster hearts is due to agonist-dependent desensitization, we investigated the effects of prolonged treatment with beta-adrenoceptor antagonists on cardiac beta-adrenergic signaling. Groups of hamsters aged 240 days received either drinking water, or drinking water containing metoprolol (10 or 100 mg/kg/day) or propranolol (4 or 40 mg/kg/day). After 4 weeks' treatment animals were killed and heart ventricles were prepared for determination of beta1- and beta2-adrenoceptor densities and their functional contribution to stimulation of adenylyl cyclase. Markers of myocardial hypertrophy, i.e. absolute and relative ventricular weight and 5-nucleotidase activity, were not affected by the different treatment regimens. Neither absolute densities nor relative proportions of beta-adrenoceptor subtypes differed between untreated and treated hamster groups. Metoprolol had no effects on the functional efficacy of beta1- and beta2-adrenoceptors. Hamsters treated with high dose propranolol showed unchanged beta1-adrenoceptor function but reduced beta2-adrenergic stimulation of adenylyl cyclase. The findings of the present study demonstrate that the disturbed coupling of cardiac beta1-adrenoceptors to adenylyl cyclase cannot be reversed by in vivo treatment with beta-adrenoceptor antagonists and, therefore, is unlikely to be due to agonist-dependent desensitization.

Three-dimensional distribution of myocardial fibrosis in the new J-2-N cardiomyopathic hamster: comparison with electrocardiographic findings

Using the new J-2-N strain of cardiomyopathic hamster obtained by cross-breeding Bio 14.6 and Golden hamsters, we investigated the three-dimensional distribution of ventricular myocardial fibrosis and compared it with electrocardiographic (ECG) changes. Twelve-lead ECG recordings were made by our own method. The hearts were cut into serial sections and subjected to light microscopic examination. The distribution, density, and volume of myocardial interstitial fibrosis and replacement fibrosis due to myocardial degeneration (F%) were visualized three-dimensionally using the TRI system (TRI; Three-Dimensional Reconstruction Image; Ratoc System Engineering, Tokyo, Japan). Thirty-two J-2-N hamsters were divided into two groups; one group comprised 17 animals with normal hearts and normal ECG findings similar to those of Golden hamsters, and the other group of 15 hamsters had dilated hearts and abnormal ECG findings. In the normal hearts, the F% values for the right ventricle, left ventricle, and ventricular septum were 6.4 +/- 0.94, 6.5 +/- 0.95, and 6.5 +/- 0.98 (mean +/- SD), respectively. The dilated hearts showed marked fibrosis, which was distributed mainly in the middle layer of the left ventricle and the ventricular septum. The corresponding F% values for the hamsters with cardiac enlargement were 19 +/- 2.6, 19 +/- 1.8, and 22 +/- 3.2 (mean +/- SD), respectively. Replacement of myocytes by fibrosis seemed to correspond to abnormal Q waves in the anterior chest leads and left axis deviation of the QRS complex.

The cardiomyopathy of the Syrian hamster (strain BIO 8262)--hypertrophic or dystrophic?

Chemical as well as cytophotometric studies were carried out on myocardium of cardiomyopathic hamsters of strain BIO 8262 and of healthy control hamsters of strain CLAC. Our interest was to find out whether the cardiomyopathic hamsters suffer from hypertrophic cardiomyopathy or not. The heart muscle mass was only slightly increased in the older cardiomyopathic hamsters when compared with the controls. This increase was accompanied by an elevated content of total DNS, RNS and protein. Furthermore, the number of hyperdiploid heart muscle cells was slightly increased in the older diseased animals. However, all these changes were of minor degree. Thus, a distinct hypertrophying process in the myocardium of the cardiomyopathic hamsters can be excluded. On the other hand, the connective tissue components (polysaccharides and collagen) were distinctly increased in the hearts of older cardiomyopathic hamsters. This is in accordance with morphological investigations, in which replacement of necrotic myocardium by fibrosis could be detected.