Microscopic Studies of Skin Blood Vessels in Relation to Sympathetic Nerve Stimulation

Abstract

Studies have been made of the diameters of microscopic and macroscopic blood vessels in the leg skin of 8 dogs and 13 cats, under pentobarbital anesthesia in parallel with observations on blood pressures in similar vessels, using two techniques, micro-cannulation and a recently described micro-chamber method. During stimulation of the homolateral sympathetic trunk, with or without curarization, there was a rise in venule and small vein pressure, associated with an initial decrease in venous vessel diameter. After cessation of stimulation the venous diameters returned to or exceeded control values while the arteriolar diameters were still markedly reduced. These observations provide direct evidence that even in the absence of mechanical obstruction to venous blood flow the pressures in venules, and therefore necessarily in capillaries when blood is flowing forward, may be elevated by sympathetic nerve stimulation which reduces the blood flow into the vascular bed in question. The possible importance of this mechanism in edema formation and in blood pooling is pointed out.