Effect of chronic administration of verapamil in Duchenne muscular dystrophy.

1. In DMD patients the effect of chronic treatment with verapamil was investigated in the p-nitrophenylphosphatase from erythrocytes, the CK and LDH in serum and the functional activity of the muscle. 2. A different behaviour in the p-nitrophenylphosphatase from untreated compared to treated DMD patients and controls is supported by the following findings: (a) values of "n" altered in F- inhibition of the enzyme with Hill coefficients -1.43, -2.18 and -2.19; (b) Arrhenius plots between 16 and 40 degrees C with inflection points for the enzyme from treated DMD patients and controls and not from untreated DMD patients. 3. Although CK and LDH in serum and the muscular evaluation showed no statistical difference between both groups, evidence is presented that in treated DMD patients the interaction membrane-enzyme is different from untreated DMD patients.