Muscle regeneration. The effect of hypophysectomy on cell proliferation and expression of insulin-like growth factor-I.
Against the background of the importance of growth hormone (GH) for normal muscle growth, a study was performed to investigate whether lack of GH after hypophysectomy affects the cell proliferation and the local production of insulin-like growth factor-I (IGF-I) in the early stages of muscle regeneration in adult rats. The level of IGF-I in the serum of hypophysectomised rats was reduced to about 30% of that of controls. The incorporation of [methyl-3H]thymidine into the regenerating muscle showed a peak 6 days after the operation and then gradually declined to the end of the period of study 30 days after initiation of regeneration by ischemic necrosis. The DNA content rose to a maximum level after 6-8 days, and remained high after 30 days. There was no major difference in the incorporation of [3H]thymidine in regenerating muscle of hypophysectomised and control rats, but the DNA concentration in the regenerating muscles of hypophysectomised rats was significantly reduced after 30 days. There was a corresponding reduction in the number of nuclei per muscle fibre, indicating that hypophysectomy has a small effect on the cell proliferation during the early stages of muscle regeneration. Immunohistochemical demonstration of IGF-I in the regenerating muscle revealed the transient presence of immunoreactive material in satellite cells and myotubes after 6 to 8 days of regeneration but no immunoreactivity after 30 days. No obvious difference was observed between hypophysectomised and control rats, indicating that the endogenous production of IGF-I in regenerating skeletal muscle can occur independently of GH.
Department of Pathology, Sahlgren Hospital, Göteborg, Sweden.
H
H
Sommerland
M
M
Ullman
E
E
Jennische
A
A
Skottner
A
A
Oldfors
D000818:Animals; D001345:Autoradiography; D002455:Cell Division / Q000187:drug effects; D004247:DNA / Q000032:analysis; D005260:Female; D013006:Growth Hormone / Q000494:pharmacology; D007016:Hypophysectomy; D007150:Immunohistochemistry; D007334:Insulin-Like Growth Factor I / Q000097:blood / Q000276:immunology; D009132:Muscles / Q000166:cytology / Q000502:physiology*; D011506:Proteins / Q000032:analysis; D051381:Rats; D012038:Regeneration; D013936:Thymidine / Q000378:metabolism
D011506:Proteins; D007334:Insulin-Like Growth Factor I; D013006:Growth Hormone; D004247:DNA; D013936:Thymidine