Enhanced sensitivity of mdx mice to intramuscular injection of compound 48/80

Species-specific differences in the inflammatory response, specifically with regard to mast cells, have been proposed to explain the phenotypic variation among dystrophin-deficient humans, and mdx mice (Gorospe et al., 1994). To test this hypothesis we have intramuscularly injected a mast cell secretogogue into both dystrophin-negative mdx and dystrophin-positive normal mice. Mast cell activity was determined by measuring the activity of mast cell tryptase, while creatine kinase activity was used to determine the course of muscle damage in vivo. Area of damage around the injection site was measured at autopsy, and used as an indication of relative sensitivity to the secretogogue effect of compound 48/80. Mdx mice exhibited more damage in response to intramuscular injection than normal control mice. In addition, mdx mice showed a substantial increase in plasma tryptase activity, followed by a large increase in muscle creatine kinase activity. On the other hand, dystrophin-positive normal controls injected with 48/80 liberated little CK or tryptase activity. These results are consistent with the hypothesis that species-specific differences in mast cell activity, or sensitivity to mast cell products could account for the variation in pathology seen in dystrophin-deficient animals.