Fine Structural and Autoradiographic Study of the Adrenergic Innervation of the Dog Lateral Saphenous Vein

Abstract

The tunica media of the dog lateral saphenous vein contains 8–12 layers of predominantly circular smooth muscle fibers. Numerous nerve profiles exhibit bright green fluorescence after formaldehyde gas treatment. These profiles occur amongst the muscle cells throughout the whole thickness of the media. Electron microscopy shows such profiles to be surrounded by Schwann cell processes enveloping axons which contain large (43%) and small (57%) dense-core vesicles. Axons are separated from muscle cells by 100–300 nm; in some cases intimate contacts, ≈20 nm wide, were seen between an axon and a muscle cell projection. After incubation of the vein with exogenous radioactive noradrenaline, nerves showed a great accumulation of radioactive material. Extraneuronal tissues (muscle and connective tissue) exhibit a much lower grain density (≈15 times less), which is, however, far above background levels. The dense innervation of the vessel wall and the intimate neuromuscular relationship are considered to form the morphological basis for the speed of nerve-evoked contractile responses in this preparation, as well as for the great extent of transmitter inactivation through neuronal reuptake.

5-hydroxytryptamine and neurotransmitter release in canine blood vessels. Inhibition by low and augmentation by high concentrations.

“…19 Strips taken from this vein react strongly both to activation of the sympathetic nerves by transmural electrical stimulation 20 and to direct stimulation of the smooth muscle cells. By analyzing the action of a vasoactive substance on the smooth muscle tension and on the release of neurotransmitter under basal conditions and during different modes of stimulation it is possible to determine its separate effects on the sympathetic nerve endings and smooth muscle cells of blood vessels.…”

Increased Responsiveness of Veins to Adrenergic Stimulation in Experimental Hypertension

“…The small saphenous and cephalic veins of the rabbit are heavily innervated throughout their medial layer , and are highly responsive to NE and nerve activation. The neuromuscular cleft in this vein in the dog is com paratively small: 0.2¡xm [Coimbra et al, 1974]. Apparent alterations in sensitivity are known to result from changes in the adrenergic nerveadrenergic receptor relationship [Trendelenburg, 1963].…”

Fibroblasts and Sympathetic Innervation of Blood Vessels

“…As to the saphenous vein, there is a gradual increase in the connective tissue from the intima to the adventitia, there being no clear separation between media and adventitia. In this vessel, adrenergic nerves penetrate the whole mus cular layer [Coimbra et al, 1974], Despite these differences, fibroblast distri bution roughly paralleled adrenergic nerve distribution in all vessels; for example, only in the saphenous vein, where nerves pene trate the whole media, do fibroblasts exist throughout the whole media.…”