Growth hormone induces muscle fibre type transformation in growth hormone-deficient rats.
The effect of recombinant human growth hormone (rhGH) on growth and composition of muscle was studied in growth hormone-deficient rats (dw/dw) treated for 10 days with either rhGH (GH) or with placebo (PLA). Age-matched control rats (DW/dw) (AGE) were treated as PLA. Growth rate increased (P < 0.05) when rats were treated with rhGH and plasma insulin-like growth factor-1 concentration was higher (P < 0.05) in GH and AGE than in PLA. The wet weight of the soleus (SOL) and the extensor digitorum longus muscles (EDL) was less in PLA compared to GH and AGE (P < 0.05). In the SOL, the amount of myosin heavy chain (MHC) I was lower (69.1 +/- 1.7%) (Mean +/- SEM) in PLA compared to both GH (85.3 +/- 2.3%) and AGE (76.4 +/- 1.6%) (P < 0.05). At the same time the amount of MHC IIA/IIX was higher (30.9 +/- 2.2%) in PLA compared to GH (14.7 +/- 2.3%) and AGE (23.6 +/- 1.6% (P < 0.05)). In EDL, treatment with rhGH did not significantly affect MHC-isoforms or the fibre type composition, but 11% more MHC IIB and 11% less MHC IIA/IIX was observed in PLA compared to AGE (P < 0.05) suggesting a long-term effect of growth hormone. MHC-isoform data were confirmed using histochemistry. In addition, in the SOL, the maximal activity of 3-hydroxyacyl-CoA dehydrogenase (HAD) in GH and AGE was higher (22 and 27%, respectively) than in PLA (P < 0.05). In the EDL, no differences were observed in maximal activity of HAD. In conclusion, the data support a role for growth hormone in muscle fibre growth and differentiation.
Daugaard
J R
JR
Copenhagen Muscle Research Centre, August Krogh Institute, University of Copenhagen, Denmark.
Laustsen
J L
JL
Hansen
B S
BS
Richter
E A
EA
D000367:Age Factors; D000818:Animals; D002454:Cell Differentiation / Q000187:drug effects / Q000502:physiology; D004392:Dwarfism / Q000188:drug therapy* / Q000378:metabolism; D013006:Growth Hormone / Q000172:deficiency* / Q000494:pharmacology*; D006579:Heterozygote; D007334:Insulin-Like Growth Factor I / Q000235:genetics / Q000378:metabolism; D008297:Male; D018485:Muscle Fibers, Skeletal / Q000737:chemistry / Q000166:cytology* / Q000187:drug effects*; D018482:Muscle, Skeletal / Q000737:chemistry / Q000166:cytology; D018995:Myosin Heavy Chains / Q000032:analysis; D051381:Rats; D011922:Rats, Mutant Strains
D007334:Insulin-Like Growth Factor I; D013006:Growth Hormone; D018995:Myosin Heavy Chains