Neuropeptide Y is a cotransmitter with norepinephrine in guinea pig inferior mesenteric vein.

Neuropeptide Y (NPY) is a cotransmitter with noradrenaline in guinea pig inferior mesenteric vein. Tyrosine hydroxylase-like immunoreactivity and NPY-like immunoreactivity were colocalized in a dense network of fibers within the adventitial layer of guinea-pig inferior mesenteric vein. Vasoconstrictor responses to electrical field stimulation (0.2-64 Hz, 0.1 ms, 12 V, for 10 s) appear to be mediated primarily by norepinephrine at 0.2 to 4 Hz and by NPY at 8 to 64 Hz. NPY Y1 receptors mediate the contractile responses to both endogenous and exogenous NPY. Norepinephrine and NPY are involved in neuromuscular transmission in guinea pig mesenteric vein suggesting that the sympathetic nervous system requires the coordinated action of norepinephrine and NPY to serve capacitance.