Regulation of porcine insulin-like growth factor I and growth hormone receptor mRNA expression by energy status.
Regulation of insulin-like growth factor I (IGF-I) and growth hormone (GH) receptor mRNA in liver and muscle by energy status was assessed in 2-mo-old pigs by altering thermoregulatory demand and energy intake over a 5-wk period to produce a range of plasma IGF-I concentrations from 3.5 +/- 0.7 to 28.9 +/- 6.2 nmol/l. These values were related directly to growth rates (0.06 +/- 0.02 to 0.44 +/- 0.01 kg/day) and total hepatic IGF-I mRNA levels. Increased growth rates were accompanied by an increase in hepatic class 1 and class 2 IGF-I mRNA levels and an increase in the ratio of class 2 to class 1 IGF-I mRNA in liver, suggesting a distinct role for class 2 expression in the endocrine growth response. High levels of class 1 transcripts and a virtual absence of class 2 transcripts characterized all muscle tissues examined, and there was no correlation with plasma IGF-I levels. This suggests that growth promotion in response to increased energy status is regulated via endocrine hepatic IGF-I rather than via a paracrine response. The levels of GH receptor mRNA were positively correlated with overall growth rate (P < 0.005) in liver and negatively correlated (P < 0.05) in muscle, indicating distinct tissue-specific effects of energy status.
Weller
P A
PA
Department of Cellular Physiology, Agricultural and Food Research Council Babraham Institute, Cambridge, United Kingdom.
Dauncey
M J
MJ
Bates
P C
PC
Brameld
J M
JM
Buttery
P J
PJ
Gilmour
R S
RS
D000818:Animals; D016375:Antisense Elements (Genetics); D001483:Base Sequence; D001833:Body Temperature Regulation; D017931:DNA Primers; D004734:Energy Metabolism; D005786:Gene Expression Regulation; D006128:Growth / Q000502:physiology*; D007334:Insulin-Like Growth Factor I / Q000096:biosynthesis*; D008099:Liver / Q000254:growth & development / Q000378:metabolism*; D008969:Molecular Sequence Data; D024510:Muscle Development; D009132:Muscles / Q000378:metabolism*; D016133:Polymerase Chain Reaction; D012313:RNA / Q000302:isolation & purification; D015347:RNA Probes; D012333:RNA, Messenger / Q000032:analysis / Q000096:biosynthesis*; D011986:Receptors, Somatotropin / Q000096:biosynthesis*; D012044:Regression Analysis; D013552:Swine; D014158:Transcription, Genetic
D016375:Antisense Elements (Genetics); D017931:DNA Primers; D015347:RNA Probes; D012333:RNA, Messenger; D011986:Receptors, Somatotropin; D012313:RNA; D007334:Insulin-Like Growth Factor I