Increased Radioresistance in Mice Injected with Urethan One Day before X-Irradiation

Abstract

>Adult female (C57LxA)F/sub 1/ mice received two intraperitoneal injections of an aqueous solution of urethane (1 mg/g body wt), one day apart. Twenty-four hours after the last injection, the mice were exposed to a single acute dose of 250 kvp x rays in the midlethal or lethal range. The 30-day LD/sub 50/ for the urethane-treated mice was found to be 970 r; the LD/sub 100/ was 1010 r. The corresponding values for the control irradiated mice were 790 r and 840 r, respectively. The radioprotective effect of urethane was not seen when the drug was administered 30 minutes before irradiation, nor when the mice were irradiated 7 days after the last urethane injection. The protective effect was not duplicated by pre-radiation exposure (1 or 2 days prior) to 100 r, 200 r, or 300 r. Non-irradiated mice given two daily injections of urethane as above exhibited a marked drop within 24 hours, in the total nucleated cell count of femoral marrow and peripheral blood accompanied by a definite increase in the myeloidflymphoid cell ratio of the blood. The resultssuggest that urethane- induced alterations in cell population of bone marrow are accompanied by an increase in the number of relatively radioresistantmore » cell types, involved in myelopoiesis. (auth)« less