when the low basal heart rate of this preparation was elevated by electrical stimulation of the cardioaccelerator nerve , clonidine had a negative chronotropic effect , the degree of which was similar to that observed in intact dogs.4 clonidine neither modified baseline heart rates of dogs with denervated hearts nor the levels of heart rate which in this preparation were reduced by a sustained electrical stimulation of the right vagus or increased by intravenous infusions of either isoprenaline or noradrenaline.5 these findings indicate that in the intact dog , bradycardia induced by clonidine resulted both from a reduction of sympathetic drive and from a concomitant increase in parasympathetic tone .
C0022245
isoprenaline
C0428977
bradycardia