. Basic mechanisms in radiobiology. 90 After sublethal doses, the inhibition of citric acid synthesis in spleen and thymus was reversible. After 200 r, citric acid formation in the spleen showed an initial decrease to less than half the normal value. This was follow- ed by a gradual return toward normal. At 14 days after 200 r, the ability of the spleen to accumulate citric acid was the same as in normal animals. After 400 r, the same initial type of depression occurred but it was greater in amount and the reversal took place at a slower rate. The results of these experiments and similar findi
. Basic mechanisms in radiobiology. 90 After sublethal doses, the inhibition of citric acid synthesis in spleen and thymus was reversible. After 200 r, citric acid formation in the spleen showed an initial decrease to less than half the normal value. This was follow- ed by a gradual return toward normal. At 14 days after 200 r, the ability of the spleen to accumulate citric acid was the same as in normal animals. After 400 r, the same initial type of depression occurred but it was greater in amount and the reversal took place at a slower rate. The results of these experiments and similar findings on thymus glands are shown in Figure 2. In these studies we obtained a correlation between the X- ray exposure and amount of inhibition. A correlation between the exposure and rate of reversal was also noted with the higher dose requiring a longer time for reversal. At this point, while we are talking about low doses of X-rays, perhaps it should be mentioned that we feel that studies using sublethal amounts of radia- tion are more valuable in searching for the mechanism of acute radiation damage in animals than is the lethal dose. This viewpoint is one for which there is a great deal of supporting evidence from experiments with other toxic agents. The arsenicals, for example, produce their inhibitory effects on sulfhydryl enzymes. DAYS AFTER X-RAY Figure 2. Durationof effects of single doses of X-rays on the ability of rat tissues to accumulate citric acid after fluoroace- tate treatment. A. Spleen, 200 r. B. Thy- mus, 200 r. , 400 r. D. Thymus, 400 r, E. Liver, 200 r. F. Liver, 400 r. (This charthas been published in a paper by , Cochran and inProc. Soc. Exp. Biol. andMed. 76, 422-427 1951). at doses far below the lethal. The agents that have strong inhibitory action on cholinesterase also are effective at doses that are far below lethal. We might expect that any action that is of importance in connection with the primary bio- chemical mechani
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