Abstract
Objectives: Normal muscle growth is accompanied by capillary proliferation, which usually lags behind the increase in muscle size, causing a decline in mean capillary density (CD). It is not known, however, how the capillary distribution is affected and what impact it has on the oxygenation of the muscle.
Methods: The capillarization of soleus muscles of rats (64–425 g) was determined with the method of capillary domains. As well as quantifying CD, capillary to fiber ratio (C:F), and fiber size, this method provides a measure of the heterogeneity of capillary spacing. Capillary locations were used to mathematically model oxygenation levels within the muscle.
Results: The increase in muscle mass was largely attributable to 5-fold increase in fiber size, accompanied by a more than 3-fold rise in C:F. The mismatch between rates of angiogenesis and muscle growth resulted in a decrease in CD. However, the heterogeneity of capillary spacing was unaffected (heterogeneity index logRSD: 0.091 ± 0.013; mean ± SD) as was muscle PO2, with modal values between 4 and 60 mmHg (0.5 and 8 kPa).
Conclusions: Angiogenesis during normal muscle growth does not maintain CD, but with similar heterogeneity of capillary spacing it preserves the potential for adequate intramuscular oxygenation.
The authors appreciate the help of J.A.M. Evers and M. de Jong with the digitizing of the fibers and capillaries.