Acute hyperinsulinemia and reduced plasma free fatty acid levels decrease intramuscular triglyceride synthesis.
OBJECTIVE
To investigate the effect of acute hyperinsulinemia and the resulting decrease in plasma free fatty acid (FFA) concentrations on intramuscular TG synthesis.


METHODS
U-(13)C(16)-palmitate was infused for 3 h in anesthetized rabbits after overnight food deprivation. Arterial blood and leg muscle were sampled during the tracer infusion. Plasma samples were analyzed for free and TG-bound palmitate enrichments and concentrations. The enrichments and concentrations of palmitoyl-CoA and palmitoyl-carnitine as well as the enrichment of palmitate bound to TG were measured in muscle samples. Fractional synthetic rate (FSR) of intramuscular TG was calculated using the tracer incorporation method. The rabbits were divided into a control group and a hyperinsulinemic euglycemic clamp group. Insulin infusion decreased the rate of appearance of plasma free palmitate (2.00±0.15 vs 0.68±0.20 μmol⋅kg(-1)⋅min(-1); P<.001), decreased plasma FFA concentration (327±61 vs 72±25 nmol/mL; P<.01), decreased the total concentration of intramuscular fatty acyl-CoA plus fatty acyl-carnitine (12.1±1.6 vs 7.0±0.7 nmol/g; P<.05), and decreased intramuscular TG FSR (0.48±0.05 vs 0.21±0.06%/h; P<.01) in comparison with the control group. Intramuscular TG FSR was correlated (P<.01) with both plasma FFA concentrations and intramuscular fatty acyl-CoA concentrations.


CONCLUSIONS
Fatty acid availability is a determinant of intramuscular TG synthesis. Insulin infusion decreases plasma and intramuscular fatty acid availability and thereby decreases TG synthesis.
Metabolism Unit, Shriners Hospital for Children, University of Texas Medical Branch, Galveston, TX 77550, USA.
Xiao-jun
XJ
Zhang
Lijian
L
Wang
Demidmaa
D
Tuvdendorj
Zhanpin
Z
Wu
Noe A
NA
Rodriguez
David N
DN
Herndon
Robert R
RR
Wolfe
D000818:Animals; D006946:Hyperinsulinism / Q000097:blood / Q000378:metabolism*; D007700:Kinetics; D008297:Male; D018482:Muscle, Skeletal / Q000378:metabolism*; D010168:Palmitates / Q000097:blood / Q000378:metabolism*; D010171:Palmitoyl Coenzyme A / Q000378:metabolism; D011817:Rabbits; D014280:Triglycerides / Q000096:biosynthesis*
D010168:Palmitates; D014280:Triglycerides; D010171:Palmitoyl Coenzyme A