NEW or unusual species are being investigated for the purpose of finding animals better suited than the customary mice, rats, and dogs to test chemicals for carcinogenicity. The steppe lemming (Lagarus lagarus, Pall) has been recently introduced into cancer research (Pogosianz, Bolonina and Olshevskaja, 1960).This species was found useful in studies of skin cancer induction with certain polynuclear aromatic hydrocarbons and for transplantation experiments.Recent developments with carcinogenic aromatic amine derivatives have suggested that this class of compounds requires metabolic activation by hydroxylation on the nitrogen (Boyland, Dukes and Grover, 1963;Cramer, Miller and Miller, 1960; Heringlake, Kiese, Renner and Wenz, 1960;Irving, 1964;Miller, Cramer and Miller, 1960; Uehleke, 1964). In order to investigate their potential susceptibility to such chemicals, we determined whether steppe lemmings metabolized 2-acetamidofluorene (AAF) by N-hydroxylation, a reaction performed by a sensitive but not by a resistant species Weisburger et al., 1964a).
MATERIALS AND METHODSAnimals.-Two breeding pairs of steppe lemmings, provided by the Laboratory Animals Centre, Carshalton, Surrey, were raised in transparent plastic mouse cages using Sanicell and hay as bedding. The diet consisted of natural foodstuffs (apples, sweet potatoes, carrots and sunflower seeds) without need for supplementary water. Males were separated from the pregnant females before birth of the litters, usually consisting of 6-9 infants. Females and males were left apart for at least 3 to 4 weeks after parturition; otherwise further pregnancies resulted after the customary gestation period of about 20 days, but with smaller litters and poorer survival of the young.Healthy adult male (8) and female (6) lemmings were selected for the metabolism experiments during which they had free access to apples, carrots, and water.Chemicals.-Commercial 2-acetamidofluorene was recrystallized from 95 % ethanol. [9-14C]-2-Acetamidofluorene (specific activity of 2-33 X 106 c.p.m./mg. or 5-2 X 105 c.p.m./,umole), N-hydroxy-2-acetamidofluorene, and the other hydroxylated derivatives, namely 1-, 3-, 5-, 7-hydroxy-2-acetamidofluorene were prepared by published methods Weisburger and Weisburger, 1958).
