Neuropeptide Y release and contractile properties: differences between canine veins and arteries

During intense sympathetic activation, as occurs during hemorrhage, veins constrict to a greater degree than do arteries. This study determined if differences in the amounts or actions of the sympathetic cotransmitter neuropeptide Y released from perivascular nerves could contribute to these differences. Strips of canine mesenteric and popliteal arteries and of saphenous and portal veins were superfused, and the releases of noradrenaline and neuropeptide Y evoked by transmural stimulation were assessed. Both compounds were released in greater amounts in the veins than in the arteries. In other experiments rings of each vessel were mounted in organ chambers for isometric-tension recording. Neuropeptide Y (up to 10(-4) M) did not contract any vessel; however, at 3 x 10(-7) M it shifted the frequency-response and concentration-response curves to noradrenaline in the arteries only. In the veins neuropeptide Y had no postsynaptic effect on strong contractions. These results suggest that neuropeptide Y functions locally to affect vasoconstriction of the arteries studied, and may have a different role in the veins. Further, processes involving neuropeptide Y do not appear to account for the differences in responsiveness of these arteries as compared to the veins during intense sympathetic stimulation.