title: Skeletal muscle growth and expression of skeletal muscle alpha-actin mRNA and insulin-like growth factor I mRNA in pigs during feeding and withdrawal of ractopamine.
abstract: Sixty crossbred barrows were used to study the effect of ractopamine (a phenethanolamine/beta-adrenergic agonist) treatment and its withdrawal on muscle growth and on the relative abundance of skeletal muscle alpha-actin (sk-alpha-actin) mRNA and of liver and longissimus muscle IGF-I mRNA at 4 wk. Ractopamine was fed (20 ppm) for periods of 2, 4, and 6 wk (six pigs per group). Additional pigs (four per group) were fed ractopamine (20 ppm) for 6 wk and then slaughtered 1, 3, and 7 d after withdrawal of ractopamine. Ractopamine increased (P < .05) longisimus muscle weight and protein content, although protein concentrations were not different. The increased muscle weight and protein content attained by feeding ractopamine for 6 wk was retained when ractopamine was withdrawn. The RNA and DNA concentrations did not change, whereas total DNA and RNA content per muscle was 18 and 26.7% greater, respectively, in ractopamine-treated pigs at 4 wk, but there were no differences at 2 or 6 wk or among the withdrawal groups. The relative abundance of sk-alpha-actin mRNA in the longissimus muscle was 41 and 62% greater (P < .05) in treated animals at 2 and 4 wk but was similar to that in controls at 6 wk and during the withdrawal period. The relative abundance of IGF-I mRNA in liver and longissimus muscle was not altered with ractopamine treatment for 4 wk. These results indicate that the ractopamine-enhanced muscle growth may result from increased myofibrillar gene expression at the pretranslational level, which is maximal with short-term treatment of ractopamine.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Department of Animal Science, Michigan State University, East Lansing 48824.
authors.forename: A L
authors.initials: AL
authors.lastname: Grant
authors.forename: D M
authors.initials: DM
authors.lastname: Skjaerlund
authors.forename: W G
authors.initials: WG
authors.lastname: Helferich
authors.forename: W G
authors.initials: WG
authors.lastname: Bergen
authors.forename: R A
authors.initials: RA
authors.lastname: Merkel
mesh_terms: D000199:Actins / Q000096:biosynthesis* / Q000235:genetics; D000818:Animals; D004247:DNA / Q000032:analysis; D005786:Gene Expression Regulation; D007334:Insulin-Like Growth Factor I / Q000032:analysis / Q000235:genetics; D008099:Liver / Q000187:drug effects / Q000378:metabolism; D008297:Male; D024510:Muscle Development; D009124:Muscle Proteins / Q000096:biosynthesis; D009132:Muscles / Q000187:drug effects / Q000378:metabolism; D010627:Phenethylamines / Q000494:pharmacology*; D012333:RNA, Messenger / Q000096:biosynthesis*; D011897:Random Allocation; D013552:Swine / Q000235:genetics / Q000254:growth & development*
chemical_list: D000199:Actins; D009124:Muscle Proteins; D010627:Phenethylamines; D012333:RNA, Messenger; C060897:ractopamine; D007334:Insulin-Like Growth Factor I; D004247:DNA