Effects of hyperthyroidism, epinephrine, and diet on heart lipoprotein lipase activity

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Abstract
Rats were fasted for several days, placed on diets high in carbohydrate, fat, or containing iodinated casein so as to produce hyperthyroidism, or were chronically injected with epinephrine. Lipoprotein lipase (LPL) activities of homogenates of the hearts of these animals were determined. Significant increases in LPL activity occurred in thyrotoxic animals, in rats receiving epinephrine injections chronically, or after prolonged fasting, while significant lowering of cardiac LPL activity was observed in rats on the high-carbohydrate or high-fat diets. Single doses of fat or single injections of epinephrine had no effect. Addition of epinephrine or of triiodothyronine to heart slices or homogenates in vitro caused no LPL increases. It is postulated that adaptive changes in cardiac LPL activity may occur in response to altered needs for utilization of fatty acids by the heart. Microsomal fractions of heart cells had the highest specific LPL activities, suggesting synthesis of the enzyme by these cellular components, or activity of the enzyme at the endoplasmic reticulum.