Lipoprotein lipase in plasma after an oral fat load: relation to free fatty acids.

Lipoprotein lipase (LPL) releases fatty acids from triglyceride-rich lipoproteins for use in cellular metabolic reac- tions. How this hydrolysis, which occurs at the vascular en- dothelium, is regulated is poorly understood. A fatty acid feed- back system has been proposed by which accumulation of fatty acids impedes LPL-catalyzed hydrolysis and dissociates the en- zyme from its endothelial binding sites. We examined this hypothesis in humans who were subjected to an oral fat toler- ance test of a mixed-meal type. Plasma triglycerides, free fatty acids, and LPL activity were measured before and repeatedly during a 12-h period after intake of the fat load. Since soybean oil with a high content of linoleic fatty acid was the source of triglycerides, a distinction could be made between endogenous free fatty acids (FFA) and FFA derived directly from lipolysis of postprandial triglyceride-rich lipoproteins. Mean LPL activity was almost doubled (P < 0.01) 6 h after intake of the oral fat load. The rise in LPL activity was accompanied by an increase of plasma triglycerides and linoleic free fatty acids (18:2 FFA), but not of total plasma FFA, which instead displayed a heter- ogeneous pattern with essentially unchanged mean levels. The postprandial response of LPL activity largely paralleled the post- prandial responses of 18:2 FFA and triglycerides. The highest degree of parallelism was seen between postprandial 18:2 FFA and LPL activity levels. Furthermore, the integrated response (area under the curve, AUC) for plasma measurements of LPL correlated with the AUC for 18:2 FFA (Y = 0.40, P < 0.05), but not with the AUC for plasma triglycerides (Y = 0.21, ns). a The high degree of parallelism and significant correla- tion between postprandial plasma LPL activity and 18:2 FFA support the hypothesis of fatty acid control of endothelial LPL during physiological conditions in humans.- Karpe, F., T. Olivecruna, G. Walldius, and A. Hamsten. Lipoprotein lipase in plasma after an oral fat load: relation to free fatty acids. J. Lipid RES. 1992. 33: 975-984.