Effect of exogenous chicken growth hormone (cGH) administration on insulin-like growth factor-I (IGF-I) gene expression in domestic fowl.
The effects of chicken growth hormone (cGH) infusion on insulin-like growth factor (IGF-I) gene expression in rapidly-growing, meat-type chickens was investigated. Chicken GH was infused either continuously or in a pulsatile fashion to 8-week-old birds during a 7-day period. Following cGH infusion, both IGF-I peptide and IGF-I mRNA content were measured in selected tissues. Steady-state IGF-I mRNA abundance was determined by a solution hybridization nuclease protection assay using total cellular RNA obtained from liver, heart, kidney, spleen, epiphyseal growth plate cartilage, gastrocnemius and pectoralis muscles. Continuous infusion of cGH elicited a two-fold increase in IGF-I peptide concentration in the kidney (P < 0.05), while all other tissues remained unchanged by cGH treatment under this infusion pattern. Pulsatile cGH infusion produced a two-fold increase in IGF-I peptide content in the liver, gastrocnemius, and pectoralis muscles (P < 0.05). In contrast with the levels of IGI-I peptide, relative steady-state IGF-I mRNA content was two-fold higher in liver and spleen of birds treated continuously with cGH, but was decreased to 35 and 55% of control birds in heart and pectoralis muscle. Pulsatile cGH infusion resulted in a 64% increase in IGF-I mRNA in the liver and remained unchanged in other tissues. Under both patterns of administration, changes in IGF-I mRNA were not reflected by changes in tissue IGF-I peptide levels. Overall correlations between tissue IGF-I mRNA and peptide levels were low and not significant in the tissues studied, except for liver under pulsatile infusion, in which IGF-I peptide levels paralleled changes in IGF-I mRNA. We conclude that, in chickens, exogenous cGH treatment stimulates hepatic IGF-I transcription and translation only when the pattern of infusion mimics the natural episodic pattern of GH secretion. The low correlation between IGF-I peptide and mRNA levels in extra-hepatic tissues may indicate differential responsiveness to GH in birds, and that in some tissues IGF-I levels are under GH-independent transcriptional controls.
Rosselot
G
G
United States Department of Agriculture, Growth Biology Laboratory, Agricultural Research Service, Beltsville, MD 20705, USA.
McMurtry
J P
JP
Vasilatos-Younken
R
R
Czerwinski
S
S
D000818:Animals; D002645:Chickens; D015870:Gene Expression / Q000187:drug effects; D013006:Growth Hormone / Q000008:administration & dosage*; D006321:Heart / Q000187:drug effects; D007262:Infusions, Intravenous; D007334:Insulin-Like Growth Factor I / Q000235:genetics* / Q000378:metabolism; D007668:Kidney / Q000187:drug effects / Q000378:metabolism; D008099:Liver / Q000187:drug effects / Q000378:metabolism; D018482:Muscle, Skeletal / Q000187:drug effects / Q000378:metabolism; D009206:Myocardium / Q000378:metabolism; D010369:Pectoralis Muscles / Q000187:drug effects / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D013154:Spleen / Q000187:drug effects / Q000378:metabolism; D014018:Tissue Distribution
D012333:RNA, Messenger; D007334:Insulin-Like Growth Factor I; D013006:Growth Hormone