Release of neuropeptide Y (NPY) induced by tyramine in the isolated vas deferens of rat.

The effect of tyramine on the isolated vas deferens of rats was investigated. Tyramine induced a dose-dependent contraction which was blocked by phentolamine and disappeared in adrenergic denervated tissues. In the presence of an antiserum to neuropeptide Y (NPY), the contraction induced by concentrations of tyramine greater than 10 microM was markedly increased. In addition to inducing the release of 3H-norepinephrine (NE), tyramine evoked a concentration-dependent efflux of NPY-like immunoreactivity (NPY-LI) from synaptosomal preparations. This action was not modified either by the removal of calcium ion from the medium or by the pretreatment with tetrodotoxin (0.5 microM). Desipramine suppressed the NPY-LI release induced by tyramine apparently by the inhibition of the uptake of tyramine is suggested by the significant positive correlation between the reduction of 14C-tyramine uptake and the inhibition of NPY-LI release induced by desipramine (r = 0.946). Therefore, we suggest that tyramine does induce the release of NPY from rat vas deferens, in addition to effecting NE secretion.