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.