The Mechanism of Radiation Protection by Histamine and Other Biological Amines

Abstract
The effects in the same strain of mouse of histamine, tryptamine, [beta] phenylethylamine, epinephrine and nor-epinephrine on O2 tension in the spleen, blood pressure, and 30-day survival after a lethal dose of X-rays were followed. CBA mice were given 675 r and C57 Bl, 700r. Blood pressure was measured by a manometer connected to a cannula inserted into the carotid artery. O2 tension was measured polarographically using a Pt electrode (at 0.6 V) inserted into the spleen, the current being proportional to O2 tension. Histamine (0.3 mg.) immediately before irradiation is strongly protective for CBA mice but 10-20 mg. affords little protection to C57B1 mice. This is correlated with the depression of the blood pressure in the two strains. Although 10 [mu]g phenergan completely inhibits the blood pressure effects of histamine it only partially reverses the radio-protection. Epinephrine and nor-epinephrine (30 [mu]g.) both increase blood pressure in CBA mice, yet only epinephrine protects against radiation. Dibenamine (10 [mu]g.) partially reverses both the blood pressure and protective effects of epinephrine. Atropine abolishes both the reduction in blood pressure and the protection afforded by 20 [mu]g carbaminoylcholine. This imperfect correlation between effects on blood pressure and radiation protection contrasts with the complete quantitative correlation between protection by these drugs and combinations of drugs and reduction in O2 tension in the spleen. Reduction of O2 tension below 50% of normal protects against irradiation by whatever means it is achieved, including reduced O2 content of inspired air. Reduction of O2 tension to 10% of normal gives maximum protection, equivalent to a 30% reduction of X-ray dose.