Limitations of ractopamine to affect adipose tissue metabolism in swine.
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.
Liu
C Y
CY
Department of Animal Sciences, Purdue University, West Lafayette, IN 47907.
Grant
A L
AL
Kim
K H
KH
Ji
S Q
SQ
Hancock
D L
DL
Anderson
D B
DB
Mills
S E
SE
D000103:Acetyl-CoA Carboxylase / Q000235:genetics / Q000378:metabolism; D000273:Adipose Tissue / Q000187:drug effects* / Q000201:enzymology / Q000378:metabolism; D000818:Animals; D015152:Blotting, Northern; D015536:Down-Regulation; D005786:Gene Expression Regulation; D051272:Glucose Transporter Type 1; D051275:Glucose Transporter Type 4; D008291:Malate Dehydrogenase / Q000235:genetics / Q000378:metabolism; D008297:Male; D009004:Monosaccharide Transport Proteins / Q000235:genetics / Q000378:metabolism; D009124:Muscle Proteins; D009132:Muscles / Q000187:drug effects / Q000378:metabolism; D010627:Phenethylamines / Q000494:pharmacology*; D012333:RNA, Messenger / Q000096:biosynthesis; D013552:Swine / Q000235:genetics / Q000378:metabolism*
D051272:Glucose Transporter Type 1; D051275:Glucose Transporter Type 4; D009004:Monosaccharide Transport Proteins; D009124:Muscle Proteins; D010627:Phenethylamines; D012333:RNA, Messenger; C060897:ractopamine; D008291:Malate Dehydrogenase; C030574:malate dehydrogenase (decarboxylating); D000103:Acetyl-CoA Carboxylase