Mechanism of Certain Abnormalities of the Circulation to the Limbs in Thyrotoxicosis*

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Abstract
Resting thyrotoxic patients had increased hand and forearm blood flows in comparison to resting normal subjects. By the use of epinephrine iontophoresis the distribution of forearm blood flow between skin and skeletal muscle was determined. In thyrotoxic patients both forearm skin and forearm skeletal muscle blood flows were increased. Oxygen consumption and carbon dioxide production of forearm skeletal muscle were also increased in thyrotoxic patients. The increase in skin blood flow in these patients was mediated by cholinergic vasodilator nerve fibers as shown by decrease in forearm skin blood flow following intraarterial infusion of atropine. Atropine infusion had no effect on hand or forearm skeletal muscle blood flows, showing that cholinergic vasodilator nerve fibers are not involved in the mediation of increased blood flow to these regions.