Its Enhancement of Cardiac Performance in the Cat and Dog and Persistence of its Inotropic Action Despite Beta-Receptor Blockade with Propranolol
The action of glucagon on cardiac performance was studied in 21 isolated cat papillary muscle preparations, in 13 spontaneously beating cat atria, in 15 intact dog hearts, and in 4 isolated perfused dog hindlimbs. In each papillary muscle preparation, addition of glucagon produced marked increases in maximal developed tension, averaging 36±4.2% (SEM) (P < 0.01), and shifted the force-velocity curve upwards and to the right, indicating that contractility was augmented. Glucagon always increased the rate of the spontaneously beating atrium, the rise averaging 28.8±5.5 contractions/min (P < 0.01). In the dog, myocardial performance was markedly augmented by the administration of glucagon, 50 µg/kg iv, as indicated by an average increase of 72.2±18.4% (P < 0.01) in the left ventricular peak dP/dt and of 58.9±12.8% (P < 0.01) in force recorded by a strain gauge arch, despite an average decrease of 3.8±1.2 cm H2O (P < 0.02) in left ventricular end-diastolic pressure. Heart rate rose an average of 38.7±10.9 beats/min (P < 0.02). Small but significant decreases in peripheral vascular resistance were produced. Single intravenous injections produced effects lasting 15 to 20 minutes. Propranolol did not prevent the inotropic responses in either the cat or dog preparations but markedly decreased the chronotropic effects.
- treatment of heart failure
- cyclic AMP
- theory of beta-receptors
- comparison with catecholamines
- adenyl cyclase
- effects on vascular bed
- Accepted April 1, 1968.
- © 1968 American Heart Association, Inc.