The effect of glucagon in animals on chronic propranolol therapy

Eleven adult mongrel dogs were divided into two groups. Group 1 animals served as controls and Group 2 received propranolol (6 mg/kg/day) orally in divided doses for 15 to 21 days. Prior to cardiopulmonary bypass, cardiac output, first derivative of left ventricular pressure (dp/dt), peak systolic pressure, heart rate, and central venous pressure were recorded. The animals were then placed on cardiopulmonary bypass and subjected to 30 minutes of global ischemia at the myocardial temperature of 32 degrees C. Following cessation of cardiopulmonary bypass the baseline studies were repeated. In Group 2 animals following the repeat studies, glucagon was administered at a rate of 0.13 microgram/kg/min. The cardiac index and dp/dt were decreased by 43.3% (p less than 0.001) and 40.5% (p less than 0.001) in comparison to Group 1 animals. In Group 2 dogs, after bypass and glucagon infusion, cardiac index increased by 38% (p less than 0.02), dp/dt rose by 78% (p less than 0.05), and peak systolic pressure increased by 24.8% (p less than 0.05). These studies show the benefit of glucagon in the treatment of low cardiac output in the presence of beta-adrenergic blockade.