Activation of insulin-like growth factor gene expression during work-induced skeletal muscle growth

• Published in: The American journal of physiology Vol. 259; no. 1 Pt 1; p. E89
• Main Authors: DeVol, D L, Rotwein, P, Sadow, J L, Novakofski, J, Bechtel, P J
• Format: Journal Article
• Language: English
• Published: United States 01.07.1990
• Subjects: Animals; Female; Gene Expression Regulation; Hypertrophy; Hypophysectomy; Insulin-Like Growth Factor I - genetics; Insulin-Like Growth Factor II - genetics; Muscles - pathology; Muscles - physiology; Physical Exertion; Rats; Rats, Inbred Strains; Reference Values; RNA, Messenger - genetics; RNA, Messenger - isolation & purification; Somatomedins - genetics
• ISSN: 0002-9513
• DOI: 10.1152/ajpendo.1990.259.1.e89

We have investigated the hypothesis that there is local regulation of insulin-like growth factor (IGF) gene expression during skeletal muscle growth. Compensatory hypertrophy was induced in the soleus, a predominantly slow-twitch muscle, and plantaris, a fast-twitch muscle, in 11- to 12-wk-old female Wistar rats by unilateral cutting of the distal gastrocnemius tendon. Animals were killed 2, 4, or 8 days later, and muscles of the nonoperated leg served as controls. Muscle weight increased throughout the experimental period, reaching 127% (soleus) or 122% (plantaris) of control values by day 8. In both growing muscles, IGF-I mRNA, quantitated by a solution-hybridization nuclease-protection assay, rose by nearly threefold on day 2 and remained elevated throughout the experimental period. IGF-II mRNA levels also increased over controls. A more dramatic response was seen in hypophysectomized rats, where IGF-I mRNA levels rose by 8- to 13-fold, IGF-II values by 3- to 7-fold, and muscle mass increased on day 8 to 149% (soleus) or 133% (plantaris) of the control contralateral limb. These results indicate that signals propagated during muscle hypertrophy enhance the expression of both IGF genes, that modulation of IGF-I mRNA levels can occur in the absence of growth hormone, and that locally produced IGF-I and IGF-II may play a role in skeletal muscle growth.