An ultrastructural and histological analysis of the effects of cold acclimation on vertebrate skeletal muscle

Abstract

1. 1.|The effects of cold acclimation on the fibre size of several skeletal muscles of rats, mice, pigeons, frogs and goldfish was determined. 2. 2.|Significant decrease in fibre size was noted in the pectoralis major (superficial part) and gastrocnemius of the rat and the pectoralis (superficial part) of the pigeon. No significant change in fibre size was observed in any of the poiklotherm muscles examined. 3. 3.|Ultrastructural analysis of red muscle fibres of the rat and the pigeon showed no significant change in mitochondrial content of a given fibre size. In the frog triceps brachii, a significant increase in the mitochondrial content was observed. 4. 4.|A relationship has been established between red fibre size and mitochondrial content for several species of homeotherms which suggests that with decreased muscle fibre size, mitochondrial content increases. Cold acclimation resulted in decreased fibre size in several homeotherms with a concomitant increase in mitochondrial content. 5. 5.|In the poikilotherms examined no change occurred in muscle fibre size but mitochondria increased significantly. The significance of these results in terms of the requirements of homeotherms and poikilotherms during cold acclimation is discussed.