In vivo morphometric analysis of muscle microcirculation in dystrophic mice.

In order to test the vascular hypothesis of muscular dystrophy, the gracilis muscle in 6- to 7-week-old C57BL/6J-dy2J normal and dystrophic mice was studied using in vivo quantitative morphometric techniques to determine the total length and surface area of capillaries in which blood was flowing per unit volume of muscle. Individual capillary lengths, diameters, and red blood cell velocities were also quantified. During resting conditions, the capillary density(length per unit volume of muscle) and surface area are increased significantly in dystrophic muscle compared to normal muscle. Under fully vasodilated conditions, the capillary density and surface area are similar in normal and dystrophic muscle. Individual capillary lengths, diameters, and red blood cell velocities are also similar in normal and dystrophic muscle under resting conditions. These results indicate that, contrary to the vascular hypothesis, dystrophic muscle at rest has increased capillary density, surface area, and blood flow. It is postulated that the increased capillary density in dystrophic muscle at rest is secondary to muscle fiber breakdown.