Alcoholic cardiomyopathy in rats: inotropic responses to phenylephrine, glucagon, ouabain, and dobutamine

The inotropic responses of chronic alcoholic and control rat hearts to phenylephrine, glucagon, ouabain, and dobutamine were studied to determine if the reported beta-adrenergic subsensitivity of alcoholic rat hearts was a specific defect. Male Long-Evans rats were maintained on nutritionally-complete liquid diets for 10 to 12 months; alcoholic rats received 38% of their calories from ethanol. Dry heart weight/body weight ratios indicated an average 15% hypertrophy of the alcoholic rat hearts. The function of isolated working hearts from these animals was studied at a constant heart rate and afterload. Ventricular function curves indicated significantly lower basal function of alcoholic rat hearts, as evident from their lower peak left ventricular relaxation rate, lower isovolumic relaxation rate, and lower peak power compared to controls. The alcoholic rat hearts had significantly lower inotropic (stroke work and peak power) responses to phenylephrine, glucagon, and dobutamine compared to controls, whereas the response of the alcoholics to ouabain was not significantly different from that of controls. Oxygen supply-to-utilization ratios decreased similarly in alcoholics and controls during treatment with the inotropic agents, as a result of increases in myocardial oxygen consumption and effects on coronary flow that were similar in both groups of animals. Thus the differences in inotropic responses observed with the alcoholic rat hearts were not primarily the result of compromised oxygen supply. Rather, the decreased stroke work response of the alcoholic hearts which occurred despite an increase in oxygen consumption suggested that the alcoholic rat hearts did not utilize oxygen as efficiently as did control hearts to perform external work. This was reflected in the significant differences between alcoholics and controls in the response of calculated external work efficiency to phenylephrine, glucagon, and dobutamine. Thus, alcohol-induced cardiac hypertrophy was associated with depressed basal left ventricular contractile function and decreased responsiveness to alpha 1-adrenergic, beta 1-adrenergic, and glucagon stimulation, but the responsiveness to ouabain was not significantly affected. These characteristics are similar to those of hearts hypertrophied by other causes.