The aim of this study was to investigate neuropeptide Y (NPY)-induced vasoconstrictions in rat blood vessels and which NPY receptor subtype is involved in vasoconstrictions. NPY produced marked contractions in rat common jugular, brachial, portal, femoral and tail veins, and vena cava inferior, whereas it produced little or no contractions in rat common carotid, brachial, femoral and tail arteries, and thoracic and abdominal aortae. The maximal NPY induced contractions were larger than maximal phenylephrine (PE)-induced contractions in the veins. These NPY induced contractions were blocked by the Y, antagonists, SRL-21, and BIBP3226 but not by the Y-5 antagonist, L-152804. A Y-2 agonist, NPY (13-36), did not produce contractions. RT-PCR showed that NPY-Y-1 was the only receptor subtype in the veins indicating that NPY induced contractions are mediated through the Y-1 receptor. Pretreatment with NPY showed a rapid and long-lasting desensitization of these contractions. The marked NPY-induced contractions and its desensitization in the veins suggest the physiological relevance of NPY in the venous circulation. (C) 2003 Published by Elsevier Science Inc.