Effect of Hypoxia on the Capillarity of Guinea Pig Skeletal Muscle

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Abstract
Capillarity and fiber composition were studied by the ATPase technique in frozen muscle samples of mongrel guinea pigs from sea level (SL) (body wt: 200-637 g) and from the Peruvian Andes [South America] at 3900 m (HA) (body wt: 350-795 g). Capillary density (CD), capillary to fiber ratio (C:F), fiber cross sectional area (FCSA) and fiber composition were measured in the soleus and the central portion of the medial head of the gastrocnemius. CD was higher in the gastrocnemius (718/mm2 SL, 757/mm2 HA) than in the soleus (600/mm2 SL, 657/mm2 HA). No correlation between CD and body weight (BW) was found. Mean FCSA was linearly related to BW. At a given BW, FCSA was greater in the HA than in the SL animals. C:F increased linearly with FCSA in the SL and the HA groups but the relationships were different in the 2 muscles: C:F = 7.04 .times. 10-4 FCSA + 0.064 (r [correlation coefficient]) = .94 in the gastrocnemius, C:F = 5.54 .times. 10-4 FCSA + 0.048, r = .97, in the soleus. The soleus had only slow twitch oxidative fibers, the gastrocnemius showed 3 fiber types. No differences in fiber composition in either muscle were seen with hypoxia. Apparently the degree of hypoxia was not enough to produce changes in capillarity or in fiber composition. The increase in C:F as FCSA increases apparently maintains constant the mass of tissue perfused by 1 capillary.

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