Protective Effect of Cystamine and AET given at Various Intervals before Irradiation

Abstract

USING the spleen colony technique described by Till and McCulloch1, we investigated the dose reduction factor for cystamine on haematopoietic stem cells by examining the endogenous colonies in the spleen of control and protected mice. We found that the size of the dose reduction factor varies noticeably with the time which has elapsed between the intraperitoneal injection of cystamine and the irradiation, particularly during the first 15 min after the administration of this radioprotective substance2. In the experiments reported here mice were irradiated at a greater dose rate (436 r./min). We were thus able to shorten the irradiation time and demonstrate that cystamine showed its maximum radioprotective effect from the fourth to the sixth minute after it had been intraperi-toneally injected. Similar results were obtained with 2-p-amino ethyl isothiouronium (AET). The results will be quoted briefly in this article; they will be published in detail elsewhere.