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

Neuropeptide Y (NPY) is a cotransmitter with noradrenaline in guinea pig in ferior 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. Vasoconstrict or 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 th e sympathetic nervous system requires the coordinated action of norepinephr ine and NPY to serve capacitance. (C) 2000 Elsevier Science Inc. All rights reserved.