Tyramine-induced release of neuropeptide Y (NPY) in isolated rabbit intestine

The effect of tyramine on the contractile activity of rabbit ileal segments was studied. Treatment with tyramine initiated a short-lived, fast contraction followed first by a relaxation then by a subsequent sustained contracture. Although the mechanism of the initial fast contraction remains obscure, the relaxation was abolished by the pretreatment with a combination of phentolamine and propranolol and the sustained contracture was blocked by neuropeptide Y (NPY)-antiserum. The inhibitory effect of the NPY-antiserum was produced in a dose-dependent manner. Thus, it is suggested that tyramine induced the release of NPY to initiate the subsequent sustained contracture.