Increased capillary supply in skeletal muscle of guinea pigs acclimated to cold.

The ATPase technique was used to visualize blood capillaries and to study fiber composition in 10-micrometer transverse sections of guinea pig gastrocnemius and soleus muscles. A control group of newborn, weanling, juvenile and adult male guinea pigs (GP) (BW = 89-1274 g) was studied in a 20-24 degrees C environment (22 degrees C GP) while 2-3 week old animals were exposed continuously to 5 degrees C for 2-18 weeks before sacrifice (5 degrees C GP) (BW = 239-1074 g). Body weight gain was not affected by cold exposure; however, the gastrocnemius and soleus muscles of the 5 degrees C GP grew at a slower rate than did the muscles of the 22 degrees C GP.

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.