Chronic hypoxia does not affect guinea pig skeletal muscle capillarity

The soleus and gastrocnemius muscles of chronically hypoxic guinea pigs were analyzed for capillary supply and myoglobin concentration. Weanling male guinea pigs were exposed to a simulated altitude of 5,100 m and an average ambient temperature of 22% C for 2, 4, 6, 10 and 14 weeks (range of BW 244--965 g). The soleus and gastrocnemius-plantaris muscles of one leg were analyzed for myoglobin concentration while the soleus and medial head of the gastrocnemius of the contralateral leg were cut at the midpoint, frozen and sectioned in a cryostat. The myosin ATPase method was used to visualize fibers and capillaries. Values of muscle weight, fiber cross sectional area, capillary density, capillary to fiber ratio and the number of capillaries around the fiber were compared to the values of the same parameters from normoxic guinea pigs selected to match the average body weights of the hypoxic animals. The growth rates of the two groups were not different. No significant differences in the regression lines for the normoxic and hypoxic animals were found so that when the data were combined no significant differences in the normoxic lines were introduced by adding the values of the hypoxic animals. The myoglobin values were significantly higher only in the hypoxic soleus after 14 weeks of exposure.