Abstract
Summary
Capillarity and fiber composition were studied by the ATPase technique in frozen muscle samples of mongrel guinea pigs from sea level (SL)(body weight: 200-637 g) and from the Peruvian Andes at 3900 m (HA)(body weight: 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 always higher in the gastrocnemius (718/mm 2 SL, 757/mm 2 HA) than in the soleus (600/mm 2 SL, 657/mm 2 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 two muscles: C:F = 7.04 × 10−4 FCSA + 0.064, r = .94 in the gastrocnemius, C:F = 5.54 × 10−4 FCSA + 0.048, r = .97, in the soleus. The soleus had only slow twitch oxidative fibers, the gastrocnemius showed three fiber types. No differences in fiber composition in either muscle were observed with hypoxia. It appears that this 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 one capillary.
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