Effect of fatty acids, glucose, and insulin on hepatic glucose uptake and glycolysis.
OBJECTIVE
There is evidence from in vitro studies that fatty acids can inhibit glucose uptake in liver. However, it is uncertain whether this happens in vivo when the liver is exposed to high levels of glucose and insulin, in combination with fatty acids, after a mixed meal. This study determined the effects of a combination of fatty acids and insulin on glucokinase (GK) activity and glycolysis in primary rat hepatocytes.


METHODS
Hepatocytes were cultured with 15 mM glucose and 2 or 10 nM insulin in combination with the fatty acids palmitate, oleate, linoleate, eicosapentaenoic acid, or docosahexaenoic acid. Total GK activity and the proportion of GK in the active, unbound state were measured to determine the effect of fatty acid on the activity and cellular localization of GK. Glucose phosphorylation and glycolysis were measured in intact cells. Lactate and pyruvate synthesis and the accumulation of ketone bodies were also estimated.


RESULTS
Palmitate and eicosapentaenoic acid lowered total GK activity in the presence of 2 nM insulin, but not with 10 nM insulin. In contrast, oleate, linoleate, and docosahexaenoic acid did not alter GK activity. None of the fatty acids tested inhibited glucose phosphorylation or glycolysis in intact rat hepatocytes. In addition, GK activity was unaffected by insulin concentration.


CONCLUSIONS
Some fatty acids can act to inhibit GK activity in primary hepatocytes. However, there was no evidence that this decrease in GK activity impaired glucose phosphorylation or glycolysis. Glucose and high concentrations of insulin, which promote glucose uptake, appear to counteract any inhibitory action of fatty acids. Therefore, the presence of fatty acids in a normal mixed meal is likely to have little effect on the capacity of the liver to take up, phosphorylate, and oxidize glucose.
Swagell
Christopher Dean
CD
Cooperative Research Centre for Diagnostics, Queensland University of Technology, Brisbane, Queensland, Australia.
Morris
Charles Phillip
CP
Henly
Debra Claire
DC
D000818:Animals; D004305:Dose-Response Relationship, Drug; D005227:Fatty Acids / Q000494:pharmacology*; D005941:Glucokinase / Q000378:metabolism*; D005947:Glucose / Q000378:metabolism / Q000493:pharmacokinetics*; D006019:Glycolysis / Q000187:drug effects*; D022781:Hepatocytes / Q000378:metabolism*; D007328:Insulin / Q000494:pharmacology*; D008099:Liver / Q000166:cytology / Q000378:metabolism; D008297:Male; D010766:Phosphorylation / Q000187:drug effects*; D051381:Rats; D017208:Rats, Wistar; D013053:Spectrophotometry
D005227:Fatty Acids; D007328:Insulin; D005941:Glucokinase; D005947:Glucose