Muscles of diabetic (db/db) mice: fibre size, fibre type and the effects of a thermogenic, beta-adrenoceptor agonist.

The size and morphological characteristics of muscles from diabetic obese (db/db) mice and their normal lean littermates were investigated. The soleus muscles were similar in size in diabetic and normal mice but the biceps brachii and gastrocnemius were significantly lighter in the diabetic animals. In the biceps brachii the small size resulted from an overall reduction in fibre diameter, which was most acute in the fast white fibres, and an increase in the proportion of smaller fast intermediate fibres. Treatment of diabetic mice with BRL 26830 a thermogenic, beta-adrenoceptor agonist, restored the weight, fibre diameter and fibre type composition of the biceps brachii to that of lean littermates. This treatment also increased the weight of the gastrocnemius, together with its protein content. Since BRL 26830 restored normoglycaemia in the diabetic mice, without decreasing their body weight, we suppose that it improved insulin action in their muscles and this, in turn, stimulated muscle growth.