Disproportionately higher levels of myocardial docosahexaenoate and elevated levels of plasma and liver arachidonate in hyperthyroid rats.

The effects of hyperthyroidism on the metabolism and distribution of polyunsaturated fatty acids in rats were investigated. The animals were fed diets containing an equal amount (1% each) of linoleate and linolenate. Although the hepatic and plasma levels of the linolenate family of acids were not greatly affected by the hyperthyroidism, the heart of the hyperthyroid rat contained 425% more docosahexaenoate than did that of its euthyroid control. The hyperthyroidism was accompanied by accumulations of 85, 105, and 114% more arachidonic acid in the heart, plasma, and liver, respectively. Nevertheless, most of the total increases in plasma and liver fatty acids were due to the greater accumulations of palmitic, stearic, and oleic acids; the hepatic level of oleate was elevated by 204%. Hyperthyroid rats had 106% more total fatty acids in their hearts, this increase being due largely to the greater accumulation of polyunsaturated acids. The thyroid hormone appears to accelerate the biosynthesis of both arachidonate and docosahexaenoate, and these endogenous polyunsaturated acids are then selectively incorporated into the cardiovascular tissues. Other possible relationships between thyroid action and tissue polyenoic acids in "cold-stressed" animals are discussed.