Innervation of human omental arteries and veins and vasomotor responses to noradrenaline, neuropeptide Y, substance P and vasoactive intestinal peptide

Human omental arteries and veins are supplied with nerve fibers containing noradrenaline (NA) and neuropeptide Y (NPY); these two agents probably co-exist in perivascular sympathetic nerve fibers. Substance P (SP)- or vasoactive intestinal peptide (VIP)-containing fibers could not be detected. In studies on isolated omental vessels NA produced constriction. The results of blockade experiments suggest that human omental arteries are equipped predominantly with α₁-adrenoceptors and omental veins with a mixture of α₁- and α₂-adrenoceptors. NPY at a concentration of 10^-7 M or higher had a weak contractile effect on veins and virtually no effect on arteries. NPY at a concentration of 3 × 10^-8 M shifted the NA concentration response curve to the left in arteries (pD₂ = 5.8 for NA versus 6.6. for NA in the presence of NPY; P < 0.001) but not in veins. Both SP and VIP relaxed arteries precontracted with NA or prostaglandin F_2α (PGF_2α). The potency of SP as a relaxant agent was similar in arteries and veins; the effect of VIP was elicited at lower concentrations in veins than in arteries.