Histochemical differences in flight and leg muscles of the pigeon.

Muscle fibers of flight (pectoralis major) and leg muscles (gastrocnemius) of the adult pigeon were classified based on succinate dehydrogenase (SDH) activity and myosin adenosine triphosphatase (ATPase) activity following preincubation at various pH's. The fiber structure in semithin as well as ultrathin sections was also evaluated. The pectoral muscle was composed almost entirely of the type IIB red fiber, with type IIB white fibers representing only 3.4% of the total fibers; and the average diameter of the type IIB red fibers was 26.8μm±6.3, whereas that of the type JIB white was 50.9μm±7.9. The pectoral muscle also contained a larger amount of fat droplets and mitochondria in the type IIB red fiber, while relatively smaller amounts of fat droplets and mitochondoria were found in the IIB white fiber. These findings suggest that the major part of pigeon pectoral muscle should be categorized as a fast-twitch (alkali-stable ATPase, Type JIB) and fatigue resistant (high oxidative staining). The leg muscle of pigeon was divided into three types, the type I fiber, the type IIA and IIB fiber. Fiber diameter of the three fiber types was not much different, and the fiber population was 23.0% type I, 33.3% type IIA and 43.6% type IIB. Regarding histochemical properties, the flight and leg muscles were very different in their muscle fibers, thus reflecting the different functions of the two muscles.