Growth and skeletal muscle microvascularity in the guinea pig

Abstract

The ATPase technique was used to visualize capillaries and to determine fiber composition in thin (10 μm) transverse slices of soleus and gastrocnemius muscles of growing guinea pigs with body weights from 89 to 1274 g. Mean fiber cross-sectional area ( FCSA ) increased from 754 to 3143 μm 2 as the soleus weight increased from 0.02 to 0.28 g and from 436 to 3694 μm 2 as the gastrocnemius weight increased from 0.20 to 3.30 g. Capillary density (CD) decreased hyperbolically with increasing FCSA from 1292 to 424 cap/mm 2 and from 1529 to 547 cap/mm 2 in the presence of a concomitant increase in the number of capillaries around the fiber (CAF) from 2.49 to 5.29 and from 3.08 to 7.24 and an increase in capillary to fiber ratio ( C F ) from 0.47 to 1.78 and from 0.57 to 2.68 in the soleus and gastrocnemius, respectively. The percentage of capillaries shared by three fibers (SF = 3) decreased, while the percentage of capillaries with SF = 2 increased with increasing FCSA in both muscles. While growth caused a significant decrease in skeletal muscle CD, factors such as increased CAF, C F , and myoglobin concertration, associated with changes in fiber geometry and capillary distribution, probably compensate for the lower CD and assure adequate O 2 delivery as the guinea pigs grow.