Abstract
In. order to determine the influence of different sources of rat serum on the activities of heart and adipose tissue lipoprotein lipase (LPL), serum from hypothyroid, euthyroid and hyperthyroid rats fed either a high-carbohydrate or high-fat diet, and that from fed and fasted rats were used for assay of LPL activity. Heart LPL activity was increased in the presence of serum from high-fat-fed rats in the assay mixture compared with that assayed in the presence of serum from high-carbohydrate fed rats. Similarly, when serum from rats made hyperthyroid by intraperitoneal injection of L-thyroxine was used to activate the assay substrate, the activities of heart LPL from these animals or the enzyme obtained from hypothyroid animals were increased to levels exceeding those when normal rat serum was used to activate the substrate. In the case of adipose tissue LPL, serum from high-fat-fed or hyperthyroid rats did not stimulate the enzyme activity, although the enzyme activity of rats fed a high-carbohydrate diet was slightly increased in the presence of serum from fasted rats.
