Ultrastructure of the nerves in veins from human omentum.

To study the ultrastructural characteristics of the sympathetic nerve terminals of human omental veins, and of their relationship to the innervated smooth muscle cells, biopsy specimens were taken during abdominal surgery, rapidly fixed in glutaraldehyde/osmium and stained with uranylacetate. The results indicate that the veins have an extensive noradrenergic innervation, penetrating into the tunica media. The distance between nerve terminals partly or wholly free from enveloping Schwann cells, to the surface of smooth muscle cells ranged from 30 to 500 nm. Large dense core vesicles were prominent in both preterminals and terminal regions, while small dense core vesicles occurred mainly in terminals. Large dense core vesicles in close contact with the axolemma were occasionally observed, indicating involvement in secretion by exocytosis.