Contribution of fatty acids released from lipolysis of plasma triglycerides to total plasma fatty acid flux and tissue-specific fatty acid uptake.
There is controversy over the extent to which fatty acids (FAs) derived from plasma free FAs (FFAs) or from hydrolysis of plasma triglycerides (TGFAs) form communal or separate pools and what the contribution of each FA source is to cellular FA metabolism. Chylomicrons and lipid emulsions were labeled with [(3)H]triolein, injected into mice, and appearance in plasma of [(3)H]oleic acid was estimated, either through a steady-state approach or by compartmental modeling. [(14)C]oleic acid was included to trace plasma FFA. Eighty to 90% of triglyceride (TG) label was recovered in plasma, irrespective of tracer method or TG source. The contribution of TG lipolysis to total plasma FA turnover was 10-20%. After infusion of [(3)H]TG and [(14)C]FA, the retention of these labels varied substantially among liver, adipose tissue, and skeletal and heart muscle. Retention of TG label changed during fasting in the same direction as lipoprotein lipase (LPL) activity is regulated. We propose a model that reconciles the paradoxical 80-90% loss of TG label into plasma with LPL-directed differential uptake of TGFA in tissues. In this model, TGFAs mix locally at the capillaries with plasma FFAs, where they would lead to an increase in the local FA concentration, and hence, FA uptake. Our data indicate that a distinction between TG-derived FA and plasma FFA cannot be made.
Teusink
Bas
B
TNO Prevention and Health, Gaubius Laboratory, NL-2301 CE Leiden, the Netherlands.
Voshol
Peter J
PJ
Dahlmans
Vivian E H
VE
Rensen
Patrick C N
PC
Pijl
Hanno
H
Romijn
Johannes A
JA
Havekes
Louis M
LM
D000273:Adipose Tissue / Q000378:metabolism; D000818:Animals; D002250:Carbon Radioisotopes; D002914:Chylomicrons / Q000378:metabolism; D005215:Fasting; D005227:Fatty Acids / Q000097:blood* / Q000378:metabolism*; D007700:Kinetics; D008066:Lipolysis; D008071:Lipoprotein Lipase / Q000378:metabolism; D008099:Liver / Q000378:metabolism; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D023421:Models, Animal; D018482:Muscle, Skeletal / Q000378:metabolism; D009206:Myocardium / Q000378:metabolism; D019301:Oleic Acid / Q000097:blood; D051381:Rats; D017208:Rats, Wistar; D014280:Triglycerides / Q000097:blood*; D014304:Triolein / Q000378:metabolism; D014316:Tritium
D002250:Carbon Radioisotopes; D002914:Chylomicrons; D005227:Fatty Acids; D014280:Triglycerides; D014316:Tritium; D014304:Triolein; D019301:Oleic Acid; D008071:Lipoprotein Lipase