Opposite effects of methylene blue and ascorbate on lipid peroxidation in muscles. Correlation with the redox state. I. Experiments on satisfied frogs.

Homogenates of heart, stomach and rectus abdominis muscles of the frog have shown different degrees of malondialdehyde (MDA) formation. MDA content was highest in heart, and lowest in stomach musculature. The resultant tissue redox-state potential (RSP) and redox potential (E'0) in homogenates determined potentiometrically also showed differences with opposite signs in relation to MDA levels. An electron acceptor, methylene blue (MB), decreased but an electron donor, ascorbate (Asc), increased the MDA level in each of the muscles. These effects were dependent upon the concentration of MB and Asc and proportional to the control MDA content in each muscle. Thus an inverse interdependence between MDA level and redox state existed even when a positive change in redox potentials was induced by MB, and also when a negative change was induced by Asc. Since there was a close negative correlation between the changes of MDA concentration and redox potential in the homogenates, it is strongly suggested that the changes of redox state in muscle are implicated in the processes leading to lipid peroxidation (LP).