Cardiac vagal action and plasma levels of neuropeptide Y following intravenous injection in the dog.

Neuropeptide Y (NPY) is a 36-amino acid peptide found co-localised with catecholamines in many sympathetic postganglionic nerves. Intravenous injection of NPY (6-10 nM/kg) in dogs causes a prolonged attenuation of cardiac vagal action (30-180 min). Peripheral plasma was collected throughout this period of vagal attenuation and plasma NPY levels were measured by radioimmunoassay. The half-life of NPY in peripheral plasma was shown to be approximately 20 min (range 20-28 min). The suggestion is made that the prolonged attenuation of vagal action may be due to high circulating levels of NPY.