Prolonged non-adrenergic inhibition of cardiac vagal action following sympathetic stimulation: neuromodulation by neuropeptide Y?

After short periods of intense sympathetic activation, the action of the vagus nerve on heart rate is inhibited for periods of many minutes to several hours. This effect is not abolished by effective blockade of alpha- or beta-adrenoceptors and is not duplicated by administration of noradrenaline or isoprenaline. A similar, long lasting vagal inhibition is caused by administration of neuropeptide Y, a probable cotransmitter in sympathetic nerves.