Characterization of the release of neuropeptide Y (NPY) induced by tyramine from synaptosomal preparations of rabbit jejunum.

The effect of tyramine on the secretion of neuropeptide Y-like immunoreactivity (NPY-LI) was investigated in a synaptosomal fraction prepared from rabbit jejunum. In addition to evoking the release of norepinephrine (NE), tyramine induced a dose-dependent increase of NPY-LI secretion which was insensitive to tetrodotoxin and was not affected by the removal of calcium ions from the bathing medium. Desipramine reduced the effectiveness of tyramine but did not influence the basal output of NPY-LI. There was a positive correlation between the inhibitory effect of desipramine on the NPY release and on the uptake of [14C]tyramine into synaptosomes. Guanethidine, however, at a concentration insufficient to block the uptake of tyramine reduced the release of both NE and NPY. These data suggest that tyramine enters into nerve terminals through a desipramine-sensitive mechanism, resulting in the co-release of NE and NPY which can be reduced by guanethidine.