Norepinephrine Uptake, Smooth Muscle Sensitivity, and Metabolizing Enzyme Activity in Rabbit Veins

Abstract

Some parameters of the adrenergic neuroeffector mechanism were measured in vitro in the central ear (near the base of the ear), common jugular, pulmonary, brachial, femoral, renal, superficial cervical, cephalic, and small saphenous veins, a branch of the deep circumflex iliac vein, the parietal branch of the internal iliac vein, branches of the anterior mesenteric vein, the inferior vena cava (immediately distal to the left renal vein), and a subcutaneous vein of the back. Although extraneuronal uptake of ³H-norepinephrine was the same in all of the veins except the mesenteric, the neuronal uptake of norepinephrine varied widely. A number of veins, including the femoral and superficial cervical veins, showed no neuronal uptake, and the uptake of others, including the cephalic and mesenteric veins, was greater than that measured in any previously studied vascular tissue. The median effective dose for the contractile effect of norepinephrine on the veins was on the same order of magnitude as that for the aorta and the ear artery. Catechol-O-methyl transferase, but not monoamine oxidase, activity appeared to be related to innervation density. It is concluded that veins show a remarkable variation in the dimensions of their adrenergic parameters, particularly those related to innervation density.