Peroxisome proliferator-activated receptor (PPAR)-alpha activation lowers muscle lipids and improves insulin sensitivity in high fat-fed rats: comparison with PPAR-gamma activation.
Peroxisome proliferator-activated receptor (PPAR)-alpha agonists lower circulating lipids, but the consequences for muscle lipid metabolism and insulin sensitivity are not clear. We investigated whether PPAR-alpha activation improves insulin sensitivity in insulin-resistant rats and compared the effects with PPAR-gamma activation. Three-week high fat-fed male Wistar rats were untreated or treated with the specific PPAR-alpha agonist WY14643 or the PPAR-gamma agonist pioglitazone (both 3 mg x kg(-1) x day(-1)) for the last 2 weeks of high-fat feeding. Like pioglitazone, WY14643 lowered basal plasma levels of glucose, triglycerides (-16% vs. untreated), and leptin (-52%), and also muscle triglyceride (-34%) and total long-chain acyl-CoAs (LCACoAs) (-41%) (P < 0.05). In contrast to pioglitazone, WY14643 substantially reduced visceral fat weight and total liver triglyceride content (P < 0.01) without increasing body weight gain. WY14643 and pioglitazone similarly enhanced whole-body insulin sensitivity (clamp glucose infusion rate increased 35 and 37% and glucose disposal 22 and 15%, respectively, vs. untreated). Both agents enhanced insulin-mediated muscle glucose metabolic index (Rg') and reduced muscle triglyceride and LCACoA accumulation (P < 0.05). Although pioglitazone had more potent effects than WY14643 on muscle insulin sensitization, this was associated with its greater effect to reduce muscle LCACoA accumulation. Overall insulin-mediated muscle Rg' was inversely correlated with the content of LCACoAs (r = -0.74, P = 0.001) and with plasma triglyceride levels (r = -0.77, P < 0.001). We conclude that even though WY14643 and pioglitazone, representing PPAR-alpha and PPAR-gamma activation, respectively, may alter muscle lipid supply by different mechanisms, both significantly improve muscle insulin action in the high fat-fed rat model of insulin resistance, and this effect is proportional to the degree to which they reduce muscle lipid accumulation.
Ye
J M
JM
Garvan Institute of Medical Research, Sydney, Australia. j.ye@garvan.unsw.edu.au
Doyle
P J
PJ
Iglesias
M A
MA
Watson
D G
DG
Cooney
G J
GJ
Kraegen
E W
EW
D000818:Animals; D004041:Dietary Fats / Q000008:administration & dosage* / Q000494:pharmacology; D005947:Glucose / Q000378:metabolism; D015309:Glucose Clamp Technique; D006946:Hyperinsulinism / Q000378:metabolism; D007333:Insulin Resistance / Q000502:physiology*; D050356:Lipid Metabolism; D008297:Male; D018482:Muscle, Skeletal / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D018160:Receptors, Cytoplasmic and Nuclear / Q000502:physiology*; D012016:Reference Values; D014157:Transcription Factors / Q000502:physiology*
D004041:Dietary Fats; D018160:Receptors, Cytoplasmic and Nuclear; D014157:Transcription Factors; D005947:Glucose