ORIGINAL ARTICLE

Effect of testosterone and endurance training on glycogen metabolism in skeletal muscle of chronic hyperglycaemic female rats

E van Breda, H Keizer, H Kuipers and G Kranenburg

Nutrition and Toxicology Research Institute Maastricht (NUTRIM), Maastricht University, Maastricht, The Netherlands

Correspondence to:
Correspondence to:
Dr van Breda, PO Box 616, Maastricht, Li 6200 MD, The Netherlands;eric.vanbreda{at}bw.unimaas.nl

Objectives: To investigate in glycolytic and oxidative muscles of trained (nine weeks) and untrained hyperglycaemic female rats the effect of hyperandrogenicity and/or endurance training on energy metabolic properties.

Methods: Glycogen content and activity of muscle enzymes with regulatory functions in glycogen synthesis were examined.

Results: Testosterone treatment increased glycogen content of extensor digitorum longus (EDL) and soleus muscles of hyperglycaemic sedentary (18% and 84% respectively) and hyperglycaemic trained (7% and 16% respectively) rats. In both types of muscle of the hyperglycaemic testosterone treated exercised subgroup, less depletion of glycogen was found than in the untreated group (38% and 87% for EDL and soleus respectively).

Conclusions: The mechanisms by which training and/or hyperandrogenism alone or in combination elicits their specific effects are complex. Differences in sex, surgery, levels of hormones administered, and exercise model used may be the main reasons for the observed discrepancies. Conclusions from the results: (a) hyperandrogenism is not a primary cause of the development of insulin resistance; (b) glycogen content of slow and fast twitch muscle is increased by training through increased glycogen synthase activity. The most plausible explanation for differences between different muscle fibre types is the different levels of expression of androgen receptors in these fibres. Hyperandrogenicity therefore acts on energy metabolic variables of hyperglycaemic animals by different mechanisms in glycolytic and oxidative muscle fibres.

Keywords: female rats; glycogen metabolism; hyperandrogenicity; hyperglycaemia

Abbreviations: EDL, extensor digitorum longus; NS, non-hyperglycaemic sedentary control; NT, non-hyperglycaemic testosterone treated; HS, hyperglycaemic sedentary control; HT, hyperglycaemic testosterone treated; HTrC, hyperglycaemic trained control; HTrT, hyperglycaemic trained testosterone treated; HTrExC, hyperglycaemic exercised control; HTrExT, hyperglycaemic exercised testosterone treated; GSi, active portion of glycogen synthase; GSi+d, total glycogen synthase; GPa, active form of glycogen phosphorylase; GPa+b, total phosphorylase activity

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