Immunohistochemical distribution of neuropeptide Y and catecholamine-synthesizing enzymes in nerve fibers of the human liver.

The course and distribution of neuropeptide Y (NPY)-immunoreactive (ir) nerves in the human liver was studied using immunohistochemistry. The distribution and density of NPY-ir fibers was compared with tyrosine hydroxylase (TH) and dopamine-beta-hydroxylase (DBH) immunoreactivity, two enzymes which are markers for dopamine- and noradrenaline-synthetizing neurones. NPY-immunopositive nerve fibers were densely distributed in the perivascular plexus of the portal trials, along the vena centralis, as well as close to the sinusoids and hepatocytes. The distribution of perivascular TH-ir and DBH-ir nerve fibers was similar to that of NPY-ir nerves, with the exception of intralobular nerves, where close topographical relations to individual hepatocytes and sinusoids were rarely observed. These results suggest that NPY is present in noradrenergic perivascular nerve fibers; probably of sympathetic origin and also in other parasympathetic, presumably cholinergic nerve fibers around the sinusoids.