Effect of hypothyroidism on heat production and loss during acute exposure to cold

¹ Department of Physiology, University of Florida, College of Medicine, Gainesville, Florida; and Physiology Branch, Quartermaster Research and Engineering Center, Natick, Massachusetts

Thyroidectomy (propylthiouracil treatment) and adrenalectomy increased the rate of cooling of rats restrained and subjected to air at 5°C. At the same colonic temperature during cooling, both thyroidectomized and adrenalectomized rats maintained higher skin temperatures than control rats. Heat production (measured by oxygen consumption) was determined for thyroidectomized and control rats only. At the same colonic temperatures during cooling, thyroidectomized rats had the same heat production as controls. However, heat loss at a given colonic temperature during cooling was greater for thyroidectomized than for control rats. The inability of thyroidectomized rats to tolerate cold as well as control rats under these conditions was almost entirely due to a more rapid loss of body heat. The cause of failure of heat conservation may be related to changes in vascular reactivity induced by the hypothyroid state.