Beta-mercaptoethylamine effect on radiation dose-response characteristics of granulocyte and lymphocyte counts.

The dose-reducing effects of substances given prior to irradiation may differ according to the end point studied. A well-known example is the small effect of an injection of 3-mercaptoethylamine (MEA) on testicles as compared to bone marrow or intestines, for which local concentration differences are apparently responsible (1, 2). Opinion is divided on whether initial leukopenia is affected by the various. protective agents that cause early leukocyte recovery and reduced mortality Cronkite et at. (3, 4) reported no diminution of initial damage in mice pretreated with glutathione. Bacq et al. (5) with MEA and Dacquisto et al. (6) with 3-mercaptoethylguanidine (MEG) considered that there was little if any reduction in initial leukopenia. On the other hand, Patt et al. (7) found less depression in both granulocyte and lymphocyte counts 4 days after 800 R in rats pretreated with cysteine than in controls. Urso et al. (8), using MEG, and Doherty and Shapira (9), using S,2aminoethylisothiourea dibromide (AET), showed what appears to be a protective effect on femoral bone marrow as early as 2 days after irradiation. In the bone marrow of rats pretreated with MEA, De et al. (10) report a reduced amount of mitotic inhibition 1 day after irradiation with 500 R. In some of the studies separate granulocyte and lymphocyte counts were not stated, early granulocyte mobilization was not taken into account, and the radiation doses used were too high to allow for effects on early lymphocyte counts. In several cases mean counts were given without error terms, making it difficult to form an opinion as to whether or not significance might have emerged with greater numbers. One should, in principle, be able to distinguish between true dose-reducing effects and effects restricted to recovery (11, 12). The distinction could be masked, however, if interfering toxic effects were present. The possibility of such toxic effects of the protective agents was not discussed in the reports mentioned above.