Abnormality in fibre type distribution of soleus and plantaris muscles in non-obese diabetic Goto-Kakizaki rats.

1. Fibre type distributions of the slow soleus and fast plantaris muscles were investigated in 5-, 9- and 20-week-old male Goto-Kakizaki (GK) rats, as an animal model of non-obese diabetes, and were compared with those of age-matched non-diabetic Wistar rats. 2. Bodyweight and both soleus and plantaris muscle weights were lower in GK rats than in Wistar rats, regardless of age. In addition, both relative soleus and plantaris muscle weights per bodyweight were lower in GK rats than in Wistar rats, regardless of age. 3. In the soleus muscle, a higher percentage of type I fibres and a lower percentage of type IIA fibres were observed in 5- and 9-week-old GK rats. In addition, there were no type IIA fibres in 20-week-old GK rats. 4. In the plantaris muscle, there were no differences in fibre type distribution of 5-week-old GK rats. However, a higher percentage of type IIB fibres and a lower percentage of type I and type IIA fibres were observed in 9- and 20-week-old GK rats. In addition, there were no type I fibres in 20-week-old GK rats. 5. These results indicate that the decreased percentage of high-oxidative fibres (e.g. type IIA fibres in the soleus muscle and type I and type IIA fibres in the plantaris muscle) of the diabetic animals is concerned with an impairment in insulin sensitivity and glucose metabolism and is not related to bodyweight.