Using a tetrazolium salt (INT), three of the Krebs cycle dehydrogenase systems were studied in homogenates of four regions of the gastrointestinal tract of the rat following either x-rays or mixed gamma-neutron radiation (in the "G-I death" dose range) delivered to the whole body (WBR). Microchemical assays were done at intervals after irradiation (10-20 minutes, 1, 2, and 3 days). There was a fall in activity as early as 10-20 minutes post-irradiation which increased in magnitude by the second and third day, for all regions studied. The gamma-neutron irradiations were relatively more effective than were the x-rays in bringing about this depression in malate-, succinate- and isocitrate-dependent dehydrogenase activity. These studies clearly indicate that the activity of the three assayed Krebs cycle dehydrogenase systems in these regions of the gastrointestinal tract was below normal after exposure to whole-body radiation. The functional capacity of the Krebs cycle appears impaired which may account, in part, for some of the functional derangements seen in such animals.

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