Immediate Sensitization of Isolated Swine Arteries and Their Vasa Vasorum to Epinephrine, Acetylcholine and Histamine by Thyroxine

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Abstract
The in vitro effect of thyroxine and control compounds on the reactivity of 177 swine carotid arteries is descr. A plethysmographic technique was used. Thyroxine (5/100 million) immediately and directly increased sensitivity of arteries to l-epinephrine. This was demonstrated by both an increase in the percentage of vasoconstriction and prolongation in the duration of constriction to l-epinephrine. The reaction to acetylcholine was slightly prolonged by thyroxine. Vasoconstriction to histamine was shorter at 1/10 ppm. soln. of thyroxine. Excess or deficiency from this quantity resulted in prolongation of histamine response. Vasa vasorum flow was decreased in vessels from thryoidectomized swine. Thyroxine prolonged constriction of the vasa vasorum produced by l-epinephrine 10-fold although thyroxine alone did not cause constriction of either the arterial wall or the vasa vasorum. These results were not reproduced by the control compounds. It is suggested that the increased sensitivity of arteries to l-epine-phrine is probably due to prompt inhibition by thyroxine of the amine oxidase present in arterial walls.