Histamine-induced contraction and its potentiation by neuropeptide Y were investigated in rat blood vessels. Rat arteries and veins constricted with single concentrations of histamine dose-dependently (0.1 - 100 mu M). This histamine-induced contraction immediately desensitized. Histamine H, receptor antagonists, 1 mu M mepyramine and 1 mu M diphenhydrarnine, abolished this transient contraction completely, whereas cimethidine, phentolamine, reserpine and tetrodotoxin failed to inhibit the contraction. Histamine H, receptor mRNA level by reverse transcription-polymerase chain reaction was quite parallel to histamine H, receptor-mediated contraction, indicating that the contraction is mediated through histamine H, receptors in the smooth muscle. Neuropeptide Y (10 nM in arteries and 3 nM in veins, respectively) significantly potentiated histamine H, receptor-mediated contraction via neuropeptide Y-1 receptors in most of rat blood vessels. Since the phospholipase C inhibitors, neomycin (I MM) and 2-nitro-4-carboxyphenyl-N, N-diphenylcarbamate (NCDC, 10 mu M), respectively, specifically abolished the potentiation, the potentiation by neuropeptide Y may depend on activation of phospholipase C. (c) 2006 Elsevier Inc. All rights reserved.