Release of lipoprotein lipase to plasma by triacylglycerol emulsions. Comparison to the effect of heparin.

It was previously known that lipoprotein lipase (LPL) activity in plasma rises after infusion of a fat emulsion. To explore the mechanism we have compared the release of LPL by emulsion to that by heparin. After bolus injections of a fat emulsion (Intralipid) to rats, plasma LPL activity gradually rose 5-fold to a maximum at 6-8 min. During the same time the concentration of injected triacylglycerols (TG) decreased by about half. Hence, the time-course for plasma LPL activity was quite different from that for plasma TG. The disappearance of injected 125I-labelled bovine LPL from circulation was retarded by emulsion. This effect was more marked 30 min than 3 min after injection of the emulsion. The data indicate that the release of LPL into plasma is not solely due to binding of the lipase to the emulsion particles as such, but involves metabolism of the particles. Emulsion increased the fraction of labelled LPL found in adipose tissue, heart and the red muscle studied, but had no significant effect on the fraction found in liver. The effects of emulsion were quite different from those of heparin, which caused an immediate release of the lipase to plasma, decreased uptake of LPL in most extrahepatic tissues by 60-95%, and increased the fraction taken up in the liver.