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Journal of Electron Microscopy Advance Access published online on October 23, 2009
Journal of Electron Microscopy, doi:10.1093/jmicro/dfp053
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© The Author 2009. Published by Oxford University Press on behalf of Japanese Society of Microscopy. All rights reserved. For permissions, please e-mail: journals.permissions@oxfordjournals.org

Morphological changes in murine skeletal muscle in response to exercise and mesterolone

Karina Fontana1,2, Kathryn E. White3,*, Gerson E. R. Campos4, Maria-Alice da Cruz-Höfling2 and John B. Harris5

1 Department of Pharmacology, Faculty of Medical Sciences
2 Department of Histology and Embryology, Institute of Biology, University of Campinas—UNICAMP, P.O. Box 6109, Campinas 13083-970, SP, Brazil
3 3EM Research Services, Institute of Neuroscience, Newcastle University, Framlington Place, Newcastle upon Tyne NE2 4HH, UK
4 Department of Anatomy, Institute of Biology, P.O. Box 6109, University of Campinas—UNICAMP, Campinas 13083-970, SP, Brazil and
5 Medical Toxicology Centre, Newcastle University, Framlington Place, Newcastle upon Tyne NE2 4HH, UK

* To whom correspondence should be addressed. E-mail: k.e.white{at}ncl.ac.uk

Light and electron microscopy and quantitative morphometry were used to determine the effects of exercise and mesterolone on the soleus muscles of mice. Both exercise and mesterolone caused a significant hypertrophy of extrafusal muscle fibres. The hypertrophy of Type I fibres was greater than that of Type II fibres. There was no hyperplasia. Mitochondria were more numerous and larger than in the muscles of sedentary animals. Capillarity increased and small centrally nucleated muscle fibres appeared, usually in small clusters and most often in the muscles of animals exposed to mesterolone. A small proportion of satellite cells exhibited signs of activation but there were more in the muscles of mesterolone-treated animals than after exercise. Muscles from animals that had been both exercised and treated with mesterolone exhibited the largest changes: muscle mass and muscle fibre hypertrophy was greater than in all other groups of animals, capillarity was higher and >30% of all recognized satellite cells exhibited signs of activation. Groups of small centrally nucleated muscle fibres were commonly seen in these muscles. They appeared to be the result of splits in the form of sprouts from existing muscle fibres. With both exercise and mesterolone, alone or in combination, there was an increase in the proportion of Type I muscle fibres and a decrease in the proportion of Type II.

Keywords     soleus muscle, mesterolone, physical exercise, hypertrophy, mitochondria, satellite cells

Received     23 April 2009, accepted 22 September 2009


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