Journal of Animal Science, Vol 72, Issue 1 62-67, Copyright © 1994 by American Society of Animal Science

JOURNAL ARTICLE

Limitations of ractopamine to affect adipose tissue metabolism in swine

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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