Blood flow and oxygen consumption in active soleus and gracilis muscles in cats

The results of the present study indicate that, although there are quantitative differences, there are no fundamental, qualitative differences in the vascular and metabolic responses to muscle contraction between slow-twitch soleus muscle and fast-twitch gracilis muscle in cats. Vascularly isolated muscles were perfused under free-flow conditions and were stimulated to contract isometrically for 12 min. Venous outflow was measured with a drop counter. Resting blood flow (6.3 +/- 1.3 ml . min-1 . 100 g-1) and oxygen consumption (0.27 +/- 0.04 ml O2 . min-1 . 100g-1) in soleus muscle did not differ significantly from the respective values in gracilis muscle. Blood flow increased by as much as sixfold above control values in both soleus and gracilis muscles in response to muscle contraction. Oxygen consumption increased linearly as a function of muscle performance in both muscles. However, the oxygen cost per kilogram of force developed was about threefold greater in gracilis compared with soleus muscle. The lower oxygen cost of contraction, coupled with an apparent maximal oxygen consumption twice that of gracilis muscle, enabled soleus muscle to maintain a greater level of muscle performance.