The cytoarchitecture and capillary supply in the skeletal muscle of growing dogs
Aquin, L.; Banchero, N.
Journal of Anatomy 132(Pt 3): 341-356
1981
ISSN/ISBN: 0021-8782 PMID: 7298487 Document Number: 177427
The sternothyroid, gastrocnemius and hindlimb flexor digitorum superficialis muscles of 22 dogs were quick frozen and treated with the ATPase technique to visualize capillaries and to typify fibers. The dogs' ages ranged from 6 days to 1 yr and body weight from 224 g to 23.0 kg. In the 6 days old animals the gastrocnemius and flexor digitorum muscles contained only FG fibers and the mean fiber cross sectional areas were 67 and 89 .mu.m2, respectively. In the adult animal these muscles contained only 1-2% FG fibers. There were 56% FOG and 42% SO fibers in the flexor digitorum muscle and these numbers were reversed in the gastrocnemius muscle. The fiber cross sectional areas of the gastrocnemius and flexor digitorum muscles of the adult dog were 6347 and 5234 .mu.m2, respectively. The sternothyroid muscle showed 2 fiber types (FG and SO) even in the youngest dog. In the adult the fiber populations were similar to the other 2 muscles: FOG, 53%; SO, 40% and FG, 7%. Over the entire body weight range, the fiber cross sectional areas of the sternothyroid muscle increased from 264 to 3189 .mu.m2. There were wide variations of fiber cross sectional area within the same cross section of muscle. In the sternothyroid muscle of the adult animal the number of capillaries around the fiber was linearly related to the areas which varied greatly within the same cross section. The capillary density in each of these muscles did not change over the entire range of body weights but was higher in the sternothyroid than in the gastrocnemius or flexor digitorum muscles. The means were 705 .+-. 41, 520 .+-. 29 and 539 .+-. 28 capillaries/mm2, respectively. The capillary to fiber ratio (C/F) increased linearly with increasing fiber cross sectional area in each of the muscles. C/F ranged from 0.04-2.70, 0.07-2.83 and 0.26-2.62 in the gastrocnemius, flexor digitorum and sternothyroid muscles, respectively. The low values of capillary density were maintained constant by absolute increases in the number of capillaries in the muscles. O2 diffusion into the innermost parts of the fibers was facilitated by an increase in the ellipticity of the fibers with increasing fiber cross sectional area and by a spiralling of the capillaries around the fibers of the adult animals.