Presynaptic alpha sub(2)-adrenoreceptors affecting terminal synaptic transmission by the nervi cardiaci accelerantes in the rat

Changes in heart rate were monitored in response to supramaximal electrical stimulation of the spinal sympathetic cardiac nerves in the pithed rat. The results support the previously published conclusion that at low frequencies of nerve traffic, transmitter removal mechanisms are dominant, reducing synaptic levels to those subliminal for activating presynaptic alpha sub(2)-adrenoreceptors.