Cardiovascular effects of dobutamine, dopamine and isoproterenol on the whole animal and isolated cross-perfused atrium in dogs.

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Abstract
The right atrium of the dog was isolated and cross-perfused with arterial blood of another (donor) dog anesthetized with pentobarbital. When dobutamine, dopamine or isoproterenol was administered i.v. to the donor dog, changes were elicited. Dobutamine caused slight biphasic changes in heart rate. Dopamine induced biphasic changes in blood pressure and heart rate. Isoproterenol produced a decrease in blood pressure and a marked increase in heart rate. All 3 catecholamines induced positive chronotropic and inotropic effects in a similar fashion on the isolated atrium cross-perfused with blood of the donor dog. When injected into the cannulated sinus node artery of the isolated dog atrium, dobutamine, dopamine or isoproterenol induced monophasic positive chronotropic and inotropic effects in a dose-related manner, although the potency of each of the drugs was different. Dobutamine-induced effects were abolished by propranolol, but not modified by imipramine which significantly suppressed tyramine- and dopamine-induced effects. The difference in dobutamine-induced chronotropic effect between the whole animal and the isolated atrium may be due mainly to modification by extracardiac factors in the whole animal.