Abstract
Ractopamine (RAC) causes fat deposition and/or fatty acid synthesis reduction and increases the rate of protein synthesis and muscle growth. However, there are few scientific studies detailing the mechanism of action of RAC and its possible metabolic pathways in swine. The objective of this study was to evaluate the effect of RAC on lipid metabolism of finishing pigs. Subcutaneous and retroperitoneal fat, muscle, and blood samples were collected at slaughter. Forty pigs were fed different RAC levels (ppm): 0, 5, 10, 15, and 20. RAC did not affect lipoprotein lipase activity in any of the tissues. There were no changes in insulin levels, but a linear increase in serum triacylglycerol, total cholesterol, and HDL-cholesterol (HDL-c) was seen. The insulin-dependent glucose transport (GLUT4) and fatty acid synthase amounts present in animals' adipose tissue did not differ, but the muscle GLUT4 presented a negative quadratic effect. The smallest GLUT4 amount (0.959) was estimated for 15.5 ppm of RAC. Serum glucose increased linearly, while a linear decrease in glycogen content was detected. The results indicate that RAC acts upon lipid metabolism in order to stimulate lipolysis, while there are changes in carbohydrate metabolism that might support lean growth in these animals.
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