Comparison of the inhibitory roles of neuropeptide Y and galanin on cardiac vagal action in the dog.

Prolonged attenuation of cardiac vagal action occurs following cardiac sympathetic nerve stimulation or intravenous neuropeptide Y (NPY) injections in anaesthetised dogs. Equimolar intravenous injections of galanin (GAL) had no effect on cardiac vagal action in this species. Immunohistochemical analysis of dog stellate ganglia and cardiac muscle showed that most nerve cell bodies showing tyrosine hydroxylase immunoreactivity (TH-IR) also showed immunoreactivity to both NPY and GAL. The results are consistent with the proposal that NPY released from cardiac sympathetic nerves is responsible for the prolonged inhibition of cardiac vagal action known to be caused by such stimulation. A role for GAL, shown here to exist in cardiac sympathetic nerves in the dog, has yet to be determined.