Endothelium of human umbilical blood vessels: ultrastructural immunolocalization of neuropeptides.

Endothelial cells of human umbilical vein and artery, both in situ and in culture, were examined ultrastructurally and at the light-microscope level using either the pre-embedding peroxidase-antiperoxidase or avidin-biotin peroxidase complex immunostaining techniques. Vasoactive intestinal polypeptide (VIP), substance P (SP), calcitonin gene-related peptide (CGRP) and arginine-vasopressin (AVP) immunoreactivity were localized in subpopulations of endothelial cells of the term umbilical vein and artery. The percentage of VIP-, SP-, CGRP- and AVP-immunoreactive cells in the umbilical vein was 12, 10, 11, and 7.5%, respectively, out of a total of 5,364 cells (from 15 umbilical cords) examined. The artery contained fewer VIP-, SP-, and CGRP-immunoreactive cells, but more AVP-immunoreactive cells, than the vein. In conclusion, subpopulations of endothelial cells in the human umbilical vein and artery contain the neuropeptides VIP, SP, CGRP and AVP, although their physiological roles are not yet known.