Exogenous growth hormone induces somatotrophic gene expression in neonatal liver and skeletal muscle.
The extent to which the local somatotrophic axis is functional in extrahepatic tissues in the neonate is unclear. We therefore determined the expression of growth hormone (GH) receptor (GHR), and insulin-like growth factors I and II (IGF-I and IGF-II) mRNA in liver and skeletal muscle (longissimus) of neonatal pigs given daily intramuscular injections of either recombinant porcine GH (1 mg/kg body wt; n = 6) or saline (n = 5) for 7 days. Exogenous GH increased plasma concentrations of GH 30-fold and IGF-I threefold. Abundances of specific mRNA in liver and muscle were measured by RNase protection assays (values are arbitrary density units). In liver, GH treatment increased GHR (6.0 vs. 9.7; P < 0.01) and IGF-I (5.2 vs. 49.0; P < 0.001) but not IGF-II (19.5 vs. 17.2) mRNA. In muscle, GH treatment increased IGF-I mRNA (13.3 vs. 22.8; P < 0.05) but not GHR (8.3 vs. 9.5) or IGF-II (16.1 vs. 16.9). These results demonstrate that exogenous GH can induce local somatotrophic function predominantly in liver but also in muscle of newborn pigs. Our novel finding on the selective increase in muscle IGF-I but not GHR gene expression suggests differences in posttranscriptional regulation and/or intracellular signaling mechanisms.
Lewis
A J
AJ
Babraham Institute, Babraham, Cambridge CB2 4AT, United Kingdom.
Wester
T J
TJ
Burrin
D G
DG
Dauncey
M J
MJ
D000818:Animals; D000831:Animals, Newborn; D018507:Gene Expression Regulation, Developmental / Q000187:drug effects*; D013006:Growth Hormone / Q000097:blood / Q000235:genetics* / Q000494:pharmacology*; D007334:Insulin-Like Growth Factor I / Q000235:genetics / Q000378:metabolism; D007335:Insulin-Like Growth Factor II / Q000235:genetics / Q000378:metabolism; D008099:Liver / Q000254:growth & development / Q000502:physiology*; D024510:Muscle Development; D018482:Muscle, Skeletal / Q000254:growth & development / Q000502:physiology*; D012333:RNA, Messenger / Q000378:metabolism; D011986:Receptors, Somatotropin / Q000235:genetics; D013552:Swine; D014158:Transcription, Genetic / Q000187:drug effects
D012333:RNA, Messenger; D011986:Receptors, Somatotropin; D007334:Insulin-Like Growth Factor I; D007335:Insulin-Like Growth Factor II; D013006:Growth Hormone