The Adrenergic Innervation of Arteriovenous Anastomoses in the Subcutaneous Fascia of Rat Skin

Abstract

Stretch preparations of the subcutaneous fascia of rat trunk skin were studied using the glyoxylic acid-induced fluorescence technique for demonstrating adrenergic nerves. To facilitate the identification of blood vessels some rats were, in addition, injected intravenously with a fluorescent (FITC-dextran) tracer and some stretch preparations were subsequently stained with haematoxylin and eosin. The arteriovenous anastomoses were found to be innervated with fluorescent adrenergic nerves. Several types of arteriovenous anastomoses were identified in the subcutaneous fascia of rat trunk skin: 1) Several quite densely innervated arteriolar branches arising from the segmental subcutaneous artery and terminating in the accompanying vein and in the capillary bed. 2) Simple arteriovenous connections, with a moderately dense adrenergic innervation usually restricted to the beginning of the arteriole. 3) More specialized arteriovenous anastomoses which often showed a slightly tortuous or S-shaped course. They often had a dense adrenergic innervation and could occasionally be divided into a quite densely innervated arteriolar portion, a very densely innervated constrictory portion and an often funnel-shaped venous portion without adrenergic nerves. It is suggested that the control of arteriovenous anastomoses occurs via combined neural adrenergic and local regulatory mechanisms. Different tissue factors might not only directly influence the contractile cells of arteriovenous anastomoses but might also have their modulating influence on the adrenergic nervous discharge in the nerves innervating arteriovenous anastomoses. Sympathectomy or denervation during skin flap operation or an axon reflex occurring in the sensory nerves probably opens the adrenergically innervated arteriovenous anastomoses and so shunts an increased quantity of blood flow through rather large mainly non-nutritive blood vessels.