Hamster Cardiomyopathy: A Genetically-Transmitted Sympathetic Dystrophy? In: Beamish RE, Panagia V, Dhalla NS, editors. Pathogenesis of Stress-Induced Heart Disease. Boston: Springer US; 1985. pp. 34-43. [DOI: 10.1007/978-1-4613-2589-5_3]

Differences in cardioprotective efficacy of adrenergic receptor antagonists and Ca2+ channel antagonists in an animal model of dilated cardiomyopathy. Effects on gross morphology, global cardiac function, and twitch force

Turkey poults fed furazolidone (Fz) in high concentrations (700 ppm) develop dilated cardiomyopathy (Fz-DCM). We tested whether five cardioactive agents were cardioprotective in this model of heart failure, ie, whether they prevented dilatation and wall thinning and improved contractile performance. We compared the effects of chronic administration of a beta 1-selective and a nonselective beta-receptor antagonist, an alpha-receptor antagonist, and two Ca2+ channel antagonists in the presence of Fz administration. The greatest cardioprotection was found with treatment with either propranolol or nifedipine. At the gross morphological level, the effect of propranolol (a nonselective beta-adrenergic antagonist) was greater than the effect of atenolol (a selective beta 1-adrenergic antagonist), and the effect of nifedipine was greater than that of verapamil (Ca2+ channel antagonists), with all agents more cardioprotective than phenoxybenzamine (an alpha 1-adrenergic > alpha 2-adrenergic antagonist). Differences in cardioprotective efficacy of each agent increased with increased concentration. These data indicate that the dose and choice of a specific type of Ca2+ channel antagonist or beta-receptor antagonist might be important in the treatment of dilated cardiomyopathy. All agents that were cardioprotective caused similar functional improvements at both the whole heart and isolated muscle levels. Compared with control animals, Fz-DCM animals showed a significant reduction in peak left ventricular (LV) developed pressure (92 +/- 17 versus 143 +/- 24 mm Hg, P < .05), +dP/dt (1151 +/- 219 versus 2454 +/- 549 mm Hg/s), and -dP/dt (1128 +/- 291 versus 1875 +/- 396 mm Hg/s), with a significant increase in LV end-diastolic volumes (2.8 +/- 0.7 versus 0.16 +/- 0.1 mL for control animals, P < .05). In contradistinction, LV + dP/dt and -dP/dt values for animals receiving Fz plus a cardioactive agent that demonstrated cardioprotection were not significantly different from control values. Peak LV developed pressures were also similar for Fz animals receiving an agent that demonstrated cardioprotection and control animals not receiving any pharmacologic agent. Isolated muscles from Fz-DCM animals as well as animals receiving Fz plus cardioprotective pharmacologic agents responded normally with regard to increasing extracellular Ca2+ concentrations. Peak twitch forces were greater for animals receiving cardioprotective agents plus Fz than control animals not receiving any pharmacologic agents or Fz alone. At higher stimulation rates, Fz-DCM muscles demonstrated a significantly reduced peak twitch force (4 +/- 0.5 versus 1.5 +/- 0.4 g/mm2 for control muscles versus Fz-DCM muscles, respectively).(ABSTRACT TRUNCATED AT 400 WORDS)

Beta-blocker treatment of dilated cardiomyopathy. Beneficial effect of carteolol in mice

BACKGROUND

The effects of carteolol, a nonselective beta-adrenergic receptor blocker with intrinsic sympathomimetic activity, were compared with those of metoprolol in a murine model of viral myocarditis and dilated cardiomyopathy caused by encephalomyocarditis virus.

METHODS AND RESULTS

In the acute experiment, BALB/c and DBA/2 mice were inoculated with encephalomyocarditis virus. BALB/c mice were then given carteolol at 1 (n = 10), 10 (n = 10), 30 (n = 11), or 100 mg/kg (n = 9) daily, and DBA/2 mice were given carteolol at 1 (n = 9) or 10 mg/kg (n = 9) daily starting the day of inoculation. Controls were given distilled water (n = 23 for BALB/c mice and n = 8 for DBA/2 mice). BALB/c mice were killed on day 7, and DBA/2 mice were killed on day 14. In the subacute experiment, DBA/2 mice were inoculated with the virus and then given carteolol at 1 (n = 12) or 10 mg/kg (n = 16), or distilled water (n = 27) daily, starting on day 14. Mice were killed on day 28. Virus replication, murine survival, heart weight to body weight ratio, and histopathological findings were similar in each group in the acute and subacute experiments. In the chronic experiment, DBA/2 mice were inoculated with the virus and were then given carteolol at 1 (n = 13) or 10 mg/kg (n = 9), metoprolol at 30 mg/kg (n = 9), or distilled water (n = 31) daily, starting on day 14. Mice were killed on day 104. Heart weight to body weight ratio and histopathological scores were significantly lower in mice given carteolol than in the infected control group. Furthermore, left ventricular cavity dimension, left ventricular wall thickness, and myocardial fiber diameter of the left ventricle were significantly reduced in mice given carteolol compared with the control group. Metoprolol did not cause any significant changes compared with the control group.

CONCLUSIONS

This study suggests that carteolol prevents the development of myocardial lesions similar to those in dilated cardiomyopathy after myocarditis in the chronic stage.

Enhanced alpha 1-adrenergic responsiveness in cardiomyopathic hamster cardiac myocytes. Relation to the expression of pertussis toxin-sensitive G protein and alpha 1-adrenergic receptors

The pathogenesis of the myopathy occurring in the heart of the cardiomyopathic strain of the Syrian hamster is not well understood but is believed to be associated with abnormal calcium handling by myopathic cells. The purpose of this study was to determine whether the cardiomyopathy occurring in strain BIO 14.6 animals is associated with an enhanced alpha 1-adrenergic receptor-mediated rise in cytosolic calcium, whether a pertussis toxin-sensitive G protein is involved in coupling the alpha 1-adrenergic receptor to changes in intracellular calcium and whether enhanced alpha 1 responsiveness is associated with an increase in the level of expression of the alpha 1-adrenergic receptor or in the pertussis toxin-sensitive G protein or proteins. To test the hypothesis that the cardiomyopathic state is associated with a greater alpha 1-receptor-mediated rise in cytosolic calcium, we studied the effect of phenylephrine (in the presence of propranolol) on time-averaged cytosolic calcium concentration ([Ca2+]i) in isolated cardiac myocytes from cardiomyopathic and age-matched control hamsters. Phenylephrine caused a greater increase both in time-averaged [Ca2+]i (an increase of 48 +/- 8% versus 12 +/- 3%, p less than 0.01) and in contractility (+181 +/- 22% versus +35 +/- 9%, p less than 0.01) in cardiomyopathic than in normal cardiac myocytes. Exposure to pertussis toxin (200 ng/ml for 3 hours) attenuated the alpha 1-adrenergic receptor-mediated increase in contractility and time-averaged [Ca2+]i in both cardiomyopathic and normal cells. The level of pertussis toxin-sensitive G protein, as determined by pertussis toxin-mediated [32P]ADP-ribosylation, was 1.6-fold higher in cardiomyopathic versus normal hamster hearts. The density of alpha 1-adrenergic receptors, as measured by the antagonist radioligand [3H]prazosin and the affinity of the receptor for agonist and antagonist were similar in myopathic and normal heart membranes. Thus, in cardiac myocytes from hamsters, the alpha 1-adrenergic receptor-mediated effects on [Ca2+]i and contractility appear to be mediated by a pertussis toxin-sensitive G protein or proteins. In myocytes from cardiomyopathic hamsters, these alpha 1-adrenergic effects were increased in magnitude, as was the level of pertussis toxin-sensitive G protein, but there was no measurable alteration in the density or ligand binding properties of alpha 1-adrenergic receptors.