The effect of endogenous catecholamines and norepinephrine administration on the performance of the isolated canine heart.

Abstract

The effect of endogenous catecholamines on the ability of the isolated canine heart to handle a volume load was studied in the Starling heart-lung preparation, modified to measure coronary flow and myocardial oxygen consumption. The isolated hearts were subjected to progressively increasing volume loads, and total left ventricular output and oxygen consumption were measured. Four groups of preparations were compared; controls, preparations from reserpine-pretreated dogs (0.5 mg/kg intraperitoneally 48 hrs and again 24 hrs prior to experimentation), preparations treated with 20 mg of pronethalol and preparations infused with norepinephrine (1 Μg/min for the duration of the experiment). The results show that the isolated heart depleted of its catecholamine content, or treated with pronethalol is capable of handling the same maximal volume load as a control heart. Similarly the isolated heart subjected to an infusion of norepinephrine of 1 Μg/min does not handle a bigger maximal volume load than a control heart. One may conclude from these results that in the isolated dog heart, augmentation of myocardial function, which accompanies an increase in volume work, is neither dependent on release of endogenous catecholamines, nor is it promoted by exogenously administered catecholamines.