PHI-like immunoreactivity co-locates with the VIP-containing system in human lumbosacral spinal cord

Using a specific radioimmunoassay and immunocytochemistry, the quantitative regional distribution and localization of PHI-like immunoreactivity was studied in normal postmortem human spinal cord. The levels of PHI-like immunoreactivity were low in the cervical and thoracic region whereas the lumbar and especially sacral regions showed higher levels, with dorsal sacral concentrations exceeding ventral concentrations. Chromatographic analysis by high pressure liquid chromatography revealed that the PHI-like immunoreactivity in human spinal cord elutes slightly earlier than pure porcine PHI, and may correspond to PHM-27, a PHI-27-like peptide found in human preprovasoactive intestinal polypeptide. Immunocytochemical studies show a distinctive distribution of PHI-like immunoreactive fibres and terminals at the lumbosacral segments. The distribution of PHI-like immunoreactivity is thus similar to that of VIP, and unlike a number of other neuropeptides; with VIP, it may mark a system which has a role in the spinal control of urogenital function in man.