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This Article Full Text Full Text (PDF) All Versions of this Article: 582/3/1303    most recent jphysiol.2007.127639v1 Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Heinemeier, K. M. Articles by Schjerling, P. Search for Related Content PubMed PubMed Citation Articles by Heinemeier, K. M. Articles by Schjerling, P. Related Collections Skeletal Muscle and Exercise

¹ Institute of Sports Medicine, Bispebjerg Hospital, Copenhagen, Denmark
² Department of Physiology and Biophysics, University of California, Irvine, CA, USA
³ Department of Molecular Muscle Biology, Copenhagen Muscle Research Centre, Rigshospitalet, Copenhagen, Denmark
⁴ Department of Biomedical Sciences, University of Copenhagen, Denmark

Acute exercise induces collagen synthesis in both tendon and muscle, indicating an adaptive response in the connective tissue of the muscle–tendon unit. However, the mechanisms of this adaptation, potentially involving collagen-inducing growth factors (such as transforming growth factor--1 (TGF--1)), as well as enzymes related to collagen processing, are not clear. Furthermore, possible differential effects of specific contraction types on collagen regulation have not been investigated. 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. RNA was extracted from medial gastrocnemius and Achilles tendon tissue 24 h after the last training bout, and mRNA levels for collagens I and III, TGF--1, connective tissue growth factor (CTGF), lysyl oxidase (LOX), metalloproteinases (MMP-2 and -9) and their inhibitors (TIMP-1 and 2) were measured by Northern blotting and/or real-time PCR. In tendon, expression of TGF--1 and collagens I and III (but not CTGF) increased in response to all types of training. Similarly, enzymes/factors involved in collagen processing were induced in tendon, especially LOX (up to 37-fold), which could indicate a loading-induced increase in cross-linking of tendon collagen. In skeletal muscle, a similar regulation of gene expression was observed, but in contrast to the tendon response, the effect of eccentric training was significantly greater than the effect of concentric training on the expression of several transcripts. In conclusion, the study supports an involvement of TGF--1 in loading-induced collagen synthesis in the muscle–tendon unit and importantly, it indicates that muscle tissue is more sensitive than tendon to the specific mechanical stimulus.

(Received 4 January 2007; accepted after revision 30 May 2007; first published online 31 May 2007)
Corresponding author K. M. Heinemeier: Institute of Sports Medicine, Bispebjerg Hospital – Building 8, 1st floor, 23 Bispebjerg Bakke, DK-2400 Copenhagen NV, Denmark. Email: katjaheinemeier{at}hotmail.com

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