NITRIC-OXIDE SYNTHASE (NOS) IN THE HUMAN UMBILICAL-CORD VESSELS - AN IMMUNOHISTOCHEMICAL STUDY

Localization of nitric oxide synthase (NOS) in endothelial cells of um bilical cord vessels and in cultured human umbilical vein endothelial cells was investigated by light and electronmicroscopical (immunogold) immunohistochemistry. We observed localization of NOS-immunoreactivit y in the majority (97%) of the endothelial cells of the umbilical vein and in a subpopulation (6.7%) of endothelial cells of the umbilical a rteries. NOS was observed as well in the amniotic epithelium and in th e cells of Wharton's jelly. Immunogold labelling in human umbilical ve in endothelial cells dominated in the cellular matrix and was not asso ciated with cellular organelles. Since human umbilical vessels are uni que in lacking innervation, the functional significance of endothelium derived relaxing factor EDRF/NO in the local control of vascular flow is discussed.