Postnatal changes in capillary density of rat sternomastoid muscle.

The changes in muscle capillarity during postnatal growth have been difficult to study using standard histochemical methods. This laboratory has proposed the use of a lectin, Griffonia simplicifolia I (GSI), as a histochemical marker that may be appropriate for developing muscle. The purpose of the study was to compare the capillary densities (capillaries per muscle fiber) determined by the GSI lectin method, alkaline phosphatase-periodic acid-Schiff (APase-PAS) staining method, and by direct counting from 1-micron plastic sections. Sternomastoid muscles from 10-day or 6-wk-old rats were used. Results from the 10-day rats showed that the GSI method and the 1-micron method gave comparable results (1.44, 1.58 capillaries per fiber), which were significantly higher than that with APase-PAS (0.56). Capillary densities in the white region of the sternomastoid from 6-wk-old rats were identical (2.80) using both the GSI and APase-PAS methods. In contrast, the GSI method yielded significantly higher capillary densities in the red region than did the APase-PAS method (4.80 vs. 3.83). These results indicate that the GSI method for visualizing capillaries is a sensitive method for visualizing capillaries in muscle during the postnatal and juvenile growth period.