High fat intake lowers hepatic fatty acid synthesis and raises fatty acid oxidation in aerobic muscle in Shetland ponies

Publisher: Cambridge University Press

E-ISSN: 1475-2662|86|1|31-36

ISSN: 0007-1145

Source: British Journal of Nutrition, Vol.86, Iss.1, 2001-07, pp. : 31-36

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Abstract

The metabolic effects of feeding soyabean oil instead of an isoenergetic amount of maize starch plus glucose were studied in ponies. Twelve adult Shetland ponies were given a control diet (15 g fat/kg DM) or a high-fat diet (118 g fat/kg DM) according to a parallel design. The diets were fed for 45 d. Plasma triacylglycerol (TAG) concentrations decreased by 55 % following fat supplementation. Fat feeding also reduced glycogen concentrations significantly by up to 65 % in masseter, gluteus and semitendinosus muscles (P<0·05, P<0·01 and P<0·01 respectively). The high-fat diet significantly increased the TAG content of semitendinosus muscle by 80 % (P<0·05). Hepatic acetyl-CoA carboxylase and fatty acid synthase activities were 53 % (P<0·01) and 56 % (P<0·01) lower respectively in the high-fat group, but diacylglycerol acyltransferase activity was unaffected. Although carnitine palmitoyltransferase-I (CPT-I) activity in liver mitochondria was not influenced, fat supplementation did render CPT-I less sensitive to inhibition by malonyl-CoA. There was no significant effect of diet on the activity of phosphofructokinase in the different muscles. The activity of citrate synthase was raised significantly (by 25 %; P<0·05) in the masseter muscle of fat-fed ponies, as was CPT-I activity (by 46 %; P<0·01). We conclude that fat feeding enhances both the transport of fatty acids through the mitochondrial inner membrane and the oxidative capacity of highly-aerobic muscles. The higher oxidative ability together with the depressed rate of de novo fatty acid synthesis in liver may contribute to the dietary fat-induced decrease in plasma TAG concentrations in equines.