Induction of manganese superoxide dismutase activity in the mouse heart by X-irradiation

X-irradiation was found to cause a dose and time dependent increase in manganese superoxide dismutase (MnSOD) activity in mouse heart. After 15.4 Gy of 250 kVp X-rays, two peaks of MnSOD activity were found in irradiated heart. The initial rise reached a peak at one hour, was followed by a decline at 4 hours, and then a second peak occurred at 12 hours post-irradiation. The pattern was shown to be reproducible and specific for MnSOD. It was not due to heart hypertrophy. Investigation of the molecular mechanisms responsible for the enhancement of MnSOD activity in X-irradiated heart by enzymatic assay, antibody assay and in vivo translation studies has shown that the enhancement of MnSOD activity at the second peak was due to an increase in the synthesis of MnSOD in X-irradiated heart. The mechanism responsible for the enhancement of MnSOD activity at the first peak seems to operate at a different level of control from the second peak. Our present data suggests that some form of MnSOD precursor may exist in the normal mouse heart and may be responsible for the first peak