INFLUENCE OF ESTROGENS ON THE ACUTE X-IRRADIATION SYNDROME

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Abstract
The observation of Treadwell and coworkers that pretreatment with estradiol benzoate improves the survival of male mice after lethal X-irradiation has been confirmed. The estrogenic protective effect occurs in female mice also. Benzestrol (a synthetic estrogen), but not progesterone and testosterone, is also effective. The time of injn. of estrogen relative to the time of irradiation is critical, for estradiol is most effective when it is given 10 days before the exposure. Expts. are cited which indicate that presence of the adrenals is not essential for the estrogenic protective action. Estradiol in dosage sufficient to protect against X-rays does not influence survival after poisoning with a nitrogen mustard. A leukopenia with maximal depression around 10-14 days after estrogen injn. has been observed. The reduction in heterophils is more marked and somewhat more consistent than the lymphocyte response. Little change is noted in erythrocyte count. Leucocytes are decreased to the same levels in both the estrogen-treated and control irradiated animals, although maximal depression and recovery occur earlier in the former. The more rapid recovery of leucocytes in irradiated mice which received a prior injn. of estrogen resides in the heterophil component. The anemia of radiation is also less severe in the estrogen-treated animals. Significantly, the maximal estrogenic protective effect is observed when mice are irradiated during their leukopenic period. The possibility is considered that estrogen stimulation renders myelopoietic tissue more resistant to X-rays, perhaps because these tissues are in a proliferative phase during or shortly after the irradiation.