Histochemical evidence of changes in fuel metabolism induced in red, white and intermediate muscle fibres of streptozotocin-treated rats.

The present study provides histochemical evidence supporting the operation of the 'glucose-fatty acid cycle' in skeletal muscles taken 5 days after the administration of a single injection of streptozotocin. It also indicates that the cycle is more important in fast-oxidative-glycolytic (FOG) and slow-oxidative (SO) fibres than in fast-glycolytic (FG) fibres. Data from muscles taken 14 and 28 days after treatment suggest that lipid catabolism becomes progressively less important with time, and that muscles from longer-term diabetic rats rely on the aerobic and anaerobic breakdown of glucose by FOG and FG fibres to meet their cellular energy requirements. Although SO fibres appeared initially to be the least affected by streptozotocin-induced diabetes, the decline in their metabolic capabilities ultimately seemed to be greater than that in FOG fibres. Transformations in the biochemical characteristics of FOG and SO fibres occurred 14-28 days after streptozotocin treatment, in the absence of changes in actomyosin-ATPase activity. This supports the view that the division of skeletal muscle fibres into three or four distinct types on the basis of myosin- or actomyosin-ATPase activity is an oversimplification of the true situation.