Thyroid hormone-catecholamine interrelationship during cold acclimation in rats Compensatory role of catecholamine for altered thyroid states

: Effects of hyper- and hypothyroidism on catecholamine (CA) metabolism in the brain, adrenal glands, liver, and brown adipose tissue (BAT) were studied in adult rats during cold acclimation. Hypothyroidism was induced by the administration of propylthiouracil (PTU) and hyperthyroidism by the injection of thyroxine (T4). After 2 weeks of treatment, they were exposed to cold (5 degrees C) and sacrificed after 1 or 4 weeks. Although the body weight gain of PTU-treated rats were markedly impaired, the body temperature was maintained within normal range. They had increased cerebral dopamine, adrenal CA and BAT norepinephrine (NE) contents, enhanced cerebral tyrosine hydroxylase and adrenal dopamine beta-hydroxylase (DBH) activities and elevated [3H]dihydroalprenolol (DHA) binding to liver plasma membranes (P less than 0.01 vs controls). T4-treated rats showed an increased brain and adrenal CA only after cold exposure. The BAT NE content, DHA binding to liver plasma membranes, and [3H]guanosine diphosphate binding to BAT mitochondria were reduced by 30 to 50% from control values after 4 weeks of cold exposure. These results indicate that during cold acclimation, thyroid hormone deficiency is associated with an accelerated CA synthesis and release, which results in an enhanced BAT thermogenesis, and the hyperthyroid state suppresses CA release, hepatic DHA binding, and BAT heat production. Thus, there is a close metabolic interrelationship between thyroid hormone and CA during exposure to cold. CA appears to ameliorate thyroid hormone excess or deficiency.