Effect of Experimental Hypertriglyceridaemia on Tissue and Serum Lipoprotein Lipase Activity

Abstract Hypertriglyceridaemia was produced in rats by the intravenous infusion of Intralipid emulsion or of very low density (d < 1.006) rabbit or human lipoproteins (VLDL). Lipoprotein lipase activity was assayed, in tissues removed at the end of infusion, on serum-activated mono- and triolein emulsions at pH 8.6. Hypertriglyceridaemia resulted in a marked decrease in epididymal adipose tissue lipoprotein lipase activity and in an increase in heart enzyme activity. These changes were evident with both mono- and triolein substrates. The effects on adipose tissue enzyme activity seemed roughly dependent on the triglyceride (TG) level and, relative to TG elevation, were most pronounced in the case of VLDL infusion. Serum lipoprotein lipase activity, measured in the absence of heparin, was considerably increased suggesting that the TG-rich material "leached" the adipose tissue enzyme into the circulation. Leaching of lipoprotein lipase from adipose tissue by Intralipid emulsion or VLDL was also demonstrated in an in vitro system devoid of heparin. Contact with the TG-poor, 1.006 < d < 1.063, lipoprotein induced only a small loss in adipose tissue lipoprotein lipase activity, either in vitro or in vivo.
Intracellular lipolytic activity toward mono- and triolein, measured in adipose tissue and heart homogenates at pH 7.2 in the absence of serum, was not significantly affected by TG elevation. Thus, the observed changes in lipoprotein lipase activity seem unrelated to the intracellular lipolytic activity.
It is suggested that the low adipose tissue lipoprotein lipase activity and the retarded TG removal observed in certain hypertriglyceridaemic conditions may be secondary to the increased supply of TG-rich lipoproteins.