Evaluation of the micronucleus test in peripheral blood erythrocytes by use of the splenectomized model.

Abstract

The micronucleus (MN) test detects the effect of mu-tagenic agents on chromosomes by identification of acentricfragments and/or lost chromosomes that form micronuclei(1, 2). The spleen of some animals, including humans, is re-sponsible for removal from the circulation of erythrocyteswith MN or Howell-Jolly bodies, as well as cells with otherabnormalities (3, 4). Thus, the presence of micronucleatederythrocytes (MNE) can be considered a sign of splenic ab-sence or dysfunction (3, 5). The presence of MNE is a charac-teristic in humans after the spleen is removed, and highernumbers of MNE are found when splenectomized individu-als are exposed to genotoxic agents (4, 6, 7).The classic method for the study of MN is to count them inpolychromatic erythrocytes (PCE) of bone marrow, 24 or 48 hafter administration of the agent to be tested, because afterthis time polychromatic erythocytes become normochromatic(1, 8). Scoring of MNE from rats exposed to any chemical hasrecently been proposed as a model (9), as has the study of MNin peripheral blood PCE of mice (10, 11). The number of PCEvaries in mammalian species, however, and some healthymammals do not have PCE in peripheral blood (e.g., cows, don-keys, sheep, goats, and horses) (12). Other species, like mice,have high numbers (0.17 to 0.28%) (13), whereas species likecats have low numbers (0 to 0.11%) (12, 14). In our laboratory,the mean PCE value of 33 cats was 0.05%, compared with thatof mice, which had a value that was 80-fold higher. For this rea-son, PCE cannot be counted in all species. Thus, the count of to-tal erythrocytes (poly- and normochromatic erythrocytes) ismore appropriate in experiments of repeated exposure togenotoxic agents (7, 15).Most work has been done using a single administration ofthe agent to be tested and observing the results 24 or 48 h later,because the PCE appear in the circulation after this period be-fore becoming mature normochromatic cells. By counting thetotal erythrocytes, the number of MNE can be followed overtime or after repeated exposures (16). The aim of the study re-ported here was to determine which common laboratory spe-cies, with intact spleen or with spleen removed surgically, islikely to be a reliable model or sensitive indicator for the MNtest, using peripheral blood erythrocytes.Animals studied were 7 mongrel dogs (