Effect of glucagon on heart muscle contractility

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Abstract
Because of the increased clinical application of beta adrenergic drugs, a study was undertaken to determine in the intact beating heart in situ whether glucagon applied directly will overcome the negative inotropic effect at such blockade. The local inotropic effects of glucagon, dopamine, norepinephrine; and isoproterenol were assessed in the intact heart. A side branch of the left descending coronary artery was cannulated with a fine polyethylene catheter without interfering with blood flow in the main branch. A strain gauge was sutured in the myocardium distal to the catheter in order to detect changes in contractility induced by the local injection of the various compounds. As a control, a second gauge was sutured to the myocardium in an area of left ventricle not perfused by the descending branch. Each drug injected into the descending branch resulted in an inotropic effect isolated to the area perfused. FollOWing reserpinization, confirmed by failure to respond to tyramine, positive responses to all of the above agents injected locally were unaltered in all dogs. However, in both reserpinized and unreserpinized dogs propranolol given locally completely blocked the inotropic responses to dopamine, norepinephrine, and isoproterenol without altering the contractile response to glucagon even when the latter was given immediately following propranolol. These results further demonstrate the Tationale for using glucagon as an inotropic agent in patients who have been treated with beta adrenergic blocking agents.

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