Effect of presynaptic alpha-adrenoceptor blockade on responses to cardiac nerve stimulation in anesthetized dogs.

Phentolamine caused significant potentiation of chronotropic responses to cardioaccelerator nerve stimulation (CANS) in pentobarbital-anesthetized dogs without impairing neuronal reuptake of norepinephrine. In a separate group of dogs, desipramine produced slight augmentation of CANS responses which were potentiated further by phentolamine administration. These results provide support for the hypothesis that presynaptic alpha-adrenergic receptors play an inhibitory role in sympathetic neurotransmission and demonstrate that this mechanism is also functioning during stimulation of the cardioaccelerator nerve in pentobarbital-anesthetized dogs.