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

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Abstract
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 μM was markedly increased. In addition to inducing the release of 3H-norepinephrine (NE), tyramine evoked a concentration-dependent efflux of NPY-like immunoreactivity (NPYLI) 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 μM). 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 4C-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.