Effects of Glucagon on Atrioventricular Conduction and Ventricular Automaticity in Dogs

Abstract

The effects of glucagon, 50 µ/kg, on atrioventricular (A-V) conduction and ventricular automaticity were studied in 14 dogs. Atrial pacing was used to control the heart rate. The His bundle electrogram was recorded, and the interval from the pacing impulse (P) to the His bundle spike (H), the P-H interval, was used as a measure of A-V conduction. Ventricular automaticity was estimated in four dogs by recording vagal escape time and idioventricular rate after 60 seconds of continuous vagal stimulation. In three dogs with experimentally produced, complete heart block the effect of glucagon on idioventricular rate was estimated. When the heart rate was 250/minute, glucagon decreased the P-H interval by 30 ± 3%, from 126 ± 5 to 85 ± 5 msec ( P < 0.01). When the heart rate was 310/minute, eight dogs demonstrated second-degree A-V block before glucagon; after glucagon, seven of the eight showed 1:1 A-V conduction. Glucagon increased heart rate by 38 ± 3.5%, from 148 ± 6.6 to 205 ± 8 beats/min ( P <0.01). Propranolol, 2 mg/kg, did not block these effects on rate and A-V conduction. The vagal escape time and idioventricular rate with vagal stimulation and idioventricular rate in complete heart block did not change significantly after glucagon. Since glucagon profoundly increased the speed of A-V conduction without increasing ventricular automaticity, it may be useful in the treatment of A-V block especially in the presence of propranolol.

Effects of Glucagon on Left Ventricular Function in Man with Controlled Heart Rate

“…We demonstrated a slight reduction in atrioventricular conduction time in our patients; this is supported by Steiner et al [22], who showed a 30-percent reduction in conduction through the atrioventricular node in dogs paced at a rate of 250/min.…”

Effect of glucagon on heart muscle contractility

“…6, 12 The similarity between the cardiovascular effects of glucagon and the catecholamines 8 , 11 has caused interest in the circulatory effects of glucagon. Studies have been carried out on the effects of glucagon on myocardial contractility/-6, 10, 14 on A-V conduction/' 17 and on heart rate. 6 , 17,18 The effect of glucagon also has been studied on the isolated heart and on conscious dogs after an experimental myocardial infarction.…”

Calcium Ions and the Cardiotonic Action of Glucagon

“…The mechanism of the positive inotropic action has not been clarified. Beta-blocking agents do not abolish the action (1)(2)(3)(4). It has also been reported that the glucagon effect is unaltered by catecholamine depletion due to treatment with reserpine (2).…”