title: Short-term strength training and the expression of myostatin and IGF-I isoforms in rat muscle and tendon: differential effects of specific contraction types.
abstract: In skeletal muscle, an increased expression of insulin like growth factor-I isoforms IGF-IEa and mechano-growth factor (MGF) combined with downregulation of myostatin is thought to be essential for training-induced hypertrophy. However, the specific effects of different contraction types on regulation of these factors in muscle are still unclear, and in tendon the functions of myostatin, IGF-IEa, and MGF in relation to training are unknown. Female Sprague-Dawley rats were subjected to 4 days of concentric, eccentric, or isometric training (n = 7-9 per group) of the medial gastrocnemius, by stimulation of the sciatic nerve during general anesthesia. mRNA levels for myostatin, IGF-IEa, and MGF in muscle and Achilles' tendon were measured by real-time RT-PCR. Muscle myostatin mRNA decreased in response to all types of training (2- to 8-fold) (P < 0.05), but the effect of eccentric training was greater than concentric and isometric training (P < 0.05). In tendon, myostatin mRNA was detected, but no changes were seen after exercise. IGF-IEa and MGF increased in muscle (up to 15-fold) and tendon (up to 4-fold) in response to training (P < 0.01). In tendon no difference was seen between training types, but in muscle the effect of eccentric training was greater than concentric training for both IGF-IEa and MGF (P < 0.05), and for IGF-IEa isometric training had greater effect than concentric (P < 0.05). The results indicate a possible role for IGF-IEa and MGF in adaptation of tendon to training, and the combined changes in myostatin and IGF-IEa/MGF expression could explain the important effect of eccentric actions for muscle hypertrophy.
authors.affiliation: Institute of Sports Medicine, Bispebjerg Hospital-Bldg. 8, 1st Floor, 23 Bispebjerg Bakke, DK-2400 Copenhagen NV, Denmark. katjaheinemeier@hotmail.com
authors.forename: K M
authors.initials: KM
authors.lastname: Heinemeier
authors.forename: J L
authors.initials: JL
authors.lastname: Olesen
authors.forename: P
authors.initials: P
authors.lastname: Schjerling
authors.forename: F
authors.initials: F
authors.lastname: Haddad
authors.forename: H
authors.initials: H
authors.lastname: Langberg
authors.forename: K M
authors.initials: KM
authors.lastname: Baldwin
authors.forename: M
authors.initials: M
authors.lastname: Kjaer
mesh_terms: D000818:Animals; D005260:Female; D005786:Gene Expression Regulation; D006984:Hypertrophy; D007334:Insulin-Like Growth Factor I / Q000235:genetics / Q000378:metabolism*; D007537:Isometric Contraction / Q000502:physiology; D009119:Muscle Contraction / Q000502:physiology*; D018482:Muscle, Skeletal / Q000378:metabolism* / Q000473:pathology; D055435:Myostatin; D010805:Physical Conditioning, Animal / Q000502:physiology*; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D011897:Random Allocation; D051381:Rats; D017207:Rats, Sprague-Dawley; D013710:Tendons / Q000378:metabolism*; D016212:Transforming Growth Factor beta / Q000235:genetics / Q000378:metabolism*
chemical_list: C525913:Mstn protein, rat; D055435:Myostatin; D020033:Protein Isoforms; D012333:RNA, Messenger; D016212:Transforming Growth Factor beta; D007334:Insulin-Like Growth Factor I