Peripheral Circulatory and Metabolic Consequences of Thyrotoxicosis: III. Vascular reactivity to catecholamines and the effect of sympathetic receptor blockade on blood flow and oxygen consumption of skeletal muscle in experimental thyrotoxicosis in the dog

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Frey, H. M. M. Peripheral Circulatory and Metabolic Consequences of Thyrotoxicosis. III. Vascular reactivity to catecholamines and the effect of sympathetic receptor blockade on blood flow and oxygen consumption of skeletal muscle in experimental thyrotoxicosis in the dogs. Scand. J. din. Lab. Invest. 19, 132-142, 1967. The resistance vessels of the gracilis muscle in the anesthetized, thyrotoxic dog responded in the majority of cases to smaller doses of intra-arterially infused catecholamines than did those of normal controls. The increased sensitivity comprised both alpha- and beta-receptor functions, with some indication that it was slightly more pronounced for beta-receptors. Following sympathetic receptor blockade with Phenoxybenzamine and/or Inderal, a reduction of cardiac output ensued which was of the same relative magnitude in normal and thyrotoxic dogs. Blood flow through the gracilis muscle was reduced in both groups in proportion to the fall in cardiac output. Sympathetic receptor blockade did not reduce oxygen consumption of the gracilis muscle in either group. Total body oxygen consumption fell slightly in both groups. The fall was, however, relatively much smaller than the fall in cardiac output, and was not nearly large enough to effect a normalization of oxygen consumption in thyrotoxic dogs. It was concluded that endogenous catecholamines are important mediators in the regulation of general cardiovascular hemodynamics, but their role in maintenance of the oxygen consumption of the tissues is a relatively minor one. This pertains to both the normal and the thyrotoxic organism.

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