Capillary density of skeletal muscle in dogs exposed to simulated altitude (38556).

Abstract

A number of anatomical and physiological changes have been reported in man and in animals living in chronic hypoxia. It is generally believed that these changes are adaptative in nature, and they help the animal tolerate a low Po2 environment. Possibly these features or mechanisms are optimally developed in man and in animals native to high altitude. However, the study of the acute situation, when a lowland animal is exposed to a low oxygen environment, offers the opportunity to ascertain how fast these changes occur, and, on occasion, provides insight into the underlying mechanisms.Valdivia (1) has found that high altitude guinea pigs (at 4540 m) have a greater number of open capillaries in skeletal muscle than sea level controls. He regarded this as an important adaptative mechanism to chronic hypoxia even though muscle fiber size was approximately the same in all animals. More recently Cassin et al. (2) showed that the number of capillaries per unit surface area in skeletal muscle of rats exposed to 6,...