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Journal of Animal Science, Vol 72, Issue 1 62-67, Copyright © 1994 by American Society of Animal Science
JOURNAL ARTICLE |
C. Y. Liu, A. L. Grant, K. H. Kim, S. Q. Ji, D. L. Hancock, D. B. Anderson and S. E. Mills
Department of Animal Sciences, Purdue University, West Lafayette, IN 47907.
To determine the temporal effect of ractopamine (Rac), a phenethanolamine, on adipose lipogenic enzyme activity and gene expression, 20 crossbred barrows were fed Rac (20 mg/kg of diet) for 0, 1, 8, or 24 d before slaughter (105 +/- 1 kg). Ractopamine had no effect (P > .05) on the activity of acetyl-coenzyme A carboxylase or malic enzyme in either the middle or outer layers of subcutaneous adipose tissue. Similarly, mRNA abundance for acetyl-coenzyme A carboxylase and the glucose transport proteins Glut 1 and Glut 4 were not affected by Rac in either adipose depot. Despite the inability of Rac to affect adipose tissue metabolism, Rac increased nitrogen retention, longissimus muscle area, and alpha-actin gene expression in skeletal muscle. Results indicate that Rac was not a functional beta-adrenergic agonist toward adipose tissue in this study. We suggest that the response to Rac in adipose tissue is masked by a combination of factors including tissue insensitivity, Rac-dose limitation, inherent partial agonism of Rac, and beta-adrenoceptor down-regulation.
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