Studies of Mechanisms of Chemical Radiation Protectionin vivo

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Abstract
I. Pure oxygen respired at 45 p.s.i. gauge-pressure by rate during or immediately after whole-body x-irradiation did not significantly alter LD50 (30 days) and LD95 (30 days) survival doses, II. Oxygen respired at 60 p.s.i. gauge-pressure completely abolished the protective effect in vivo of histamine and adrenalin and substantially reduced that of 5-hydroxytryptamine (5HT). The radio-protective actions of cysteamine, cystamine, 1-cysteine and AET, were slightly reduced at 60 p.s.i., but cyanide potentiated this reduction for cystamine and 5HT. III. Polarographic measurement of tissue oxygen-tensions for oxygen respired at pressures up to 60 p.s.i. gave a linear relation between the partial pressure of oxygen respired and the subcutaneous tissue oxygen-tension. 5HT and cystamine caused a significant reduction in the slope of this line, but this seemed insufficient to explain radiochemical protection solely in terms of pharmacologically-induced intercellular anoxia. Manometric measurements of arterial and venous blood oxygen-tensions supported the polarographic findings. IV. Various agents which gave good protection against irradiation also protected against oxygen poisoning. However, in rats and mice, many other compounds tested gave marked protection against oxygen poisoning but failed to affect radiosensitivity significantly.