Capillary growth in chick skeletal muscle with normal maturation and hypertrophy.

Tissue capillarity and tissue enzyme activity (citrate synthase and lactate dehydrogenase) were determined for two red muscles and two white muscles from the domestic chicken during normal maturation and, for one red muscle, during muscle hypertrophy. Muscle fiber cross sectional area increased with muscle mass during normal maturation and with the additional increase in muscle mass following hypertrophy. Normal maturation and hypertrophy did not affect lactate dehydrogenase activity or citrate synthase activity for the muscles with anaerobic fiber types. Citrate synthase activity per unit muscle mass was positively correlated with muscle capillary density for the muscles with aerobic fiber types. Capillary to fiber ratios increased with fiber size and were significantly higher in muscles with aerobic fibers than in muscles with nonaerobic fibers. However, capillary densities decreased with maturation and with fiber hypertrophy. For each of the muscles sampled, the number of capillaries per unit linear distance of muscle fiber perimeter was independent of muscle fiber growth during normal maturation and during hypertrophy. The results from the present work are consistent with the hypothesis that muscle fiber type and muscle fiber surface area may be the primary determinants of capillary growth during normal maturation and during fiber hypertrophy.