Growth factor messenger RNA levels in muscle and liver of steroid-implanted and nonimplanted steers.
Ribonuclease protection assays were used to measure steady-state semimembranosus muscle and/or hepatic levels of IGF-I, IGFBP-3, IGFBP-5, hepatocyte growth factor (HGF), and myostatin messenger RNA (mRNA) in steers implanted from 32 to 38 d with Revalor-S, a combined trenbolone acetate and estradiol implant. Insulin-like growth factor-ImRNA levels were 69% higher (P < 0.01, n = 7) in the livers of implanted steers than in the livers of nonimplanted steers. Similarly, IGF-I mRNA levels were 50% higher (P < 0.05, n = 7) in the semimembranosus muscles of implanted steers than in the same muscles from nonimplanted steers. Hepatic IGFBP-3 mRNA levels were 24% higher (P < 0.07, n = 7) in implanted steers than in nonimplanted steers. Hepatic HGF and IGFBP-5 mRNA levels did not differ between implanted and nonimplanted steers. Similarly, muscle IGFBP-3, IGFBP-5, HGF, and myostatin mRNA levels were not affected by treatment. Previous data from these same steers have shown that circulating IGF-I and IGFBP-3 concentrations were 30 to 40% higher (P < 0.01, n = 7) in implanted steers than in nonimplanted, control steers. Additionally, the number of actively proliferating satellite cells that could be isolated from the semimembranosus muscle was 45% higher (P < 0.01, n = 7) for implanted steers than for nonimplanted steers. Viewed together, these data suggest that increased muscle IGF-I levels stimulate increased satellite cell proliferation, resulting in the increased muscle growth observed in Revalor-S implanted steers.
Animal Growth and Development Laboratory, Department of Animal Science, University of Minnesota, St. Paul 55108, USA.
M E
ME
White
B J
BJ
Johnson
M R
MR
Hathaway
W R
WR
Dayton
D045930:Anabolic Agents / Q000008:administration & dosage / Q000494:pharmacology*; D000818:Animals; D001483:Base Sequence; D002417:Cattle / Q000378:metabolism*; D004338:Drug Combinations; D004343:Drug Implants; D004958:Estradiol / Q000008:administration & dosage / Q000494:pharmacology*; D017228:Hepatocyte Growth Factor / Q000096:biosynthesis / Q000235:genetics; D018969:Insulin-Like Growth Factor Binding Proteins / Q000096:biosynthesis* / Q000235:genetics; D007334:Insulin-Like Growth Factor I / Q000096:biosynthesis* / Q000235:genetics; D008099:Liver / Q000187:drug effects / Q000378:metabolism; D008297:Male; D018482:Muscle, Skeletal / Q000187:drug effects / Q000378:metabolism; D055435:Myostatin; D016133:Polymerase Chain Reaction; D012333:RNA, Messenger / Q000378:metabolism; D016212:Transforming Growth Factor beta / Q000096:biosynthesis / Q000235:genetics; D014204:Trenbolone Acetate / Q000008:administration & dosage / Q000031:analogs & derivatives* / Q000494:pharmacology*
D045930:Anabolic Agents; D004338:Drug Combinations; D004343:Drug Implants; D018969:Insulin-Like Growth Factor Binding Proteins; D055435:Myostatin; D012333:RNA, Messenger; D016212:Transforming Growth Factor beta; D004958:Estradiol; D017228:Hepatocyte Growth Factor; D007334:Insulin-Like Growth Factor I; D014204:Trenbolone Acetate