Stuesse_1982_Am.J.Physiol_242_H7

Glucagon accelerates the heart independent of sympathetic nervous system stimulation. The effect of glucagon on the chronotropic responses to repetitive bursts of vagal stimulation was determined in open-chest anesthesized dogs. When the cervical vagi were stimulated at constant frequencies, the change in heart rate was not affected by glucagon administration, i.e., no vagolytic effect caused by glucagon was apparent. Thus glucagon did not alter the reaction of acetylcholine with cardiac postsynaptic receptors. When the vagi were stimulated intermittently with one short burst of vagal stimuli delivered each cardiac cycle, the resultant heart period was dependent on the time of vagal stimulus delivery. Both maximum and minimum cardiac cycle lengths obtained during phasic vagal stimulation were decreased by glucagon. As it has been previously demonstrated that vagal impulses to the heart tend to be clustered during certain times of the cardiac cycle, by accelerating the heart glucagon may shift the cardiac response to vagal stimulation.