AN IMPROVED METHOD FOR THE MOUSE-LIVER MICRONUCLEUS TEST

We have developed a very practical method for performing the liver mic ronucleus test in mice. Using this method, we evaluated 11 different t ypes of mutagens, including, 2-acetylaminofluorene, amsacrine, benzene , cyclophosphamide, diethylnitrosamine, 4-dimethylamino-3'-methylazobe nzene, N-ethyl-N-nitrosourea, fluorouracil, mitomycin C, potassium chr omate (VI) and selenious acid. In order to assess the sensitivity of o ur method, the peripheral blood reticulocyte micronucleus test was per formed in the same mouse. Animals were given test chemicals once and u nderwent partial hepatectomy (PH) 24 h later in order to induce mitoti c stimulation. Peripheral blood was sampled 0, 24, 48 and 72 h after t reatment. The incidence of micronucleated hepatocytes was determined 5 days after PH. As a result, diethylnitrosamine and 4-dimethylamino-3' -methylazobenzene, known as liver carcinogens, increased the incidence of micronucleated cells in the liver only. Positive reactions for ben zene, on the other hand, were found in the peripheral blood reticulocy tes only. The other chemicals showed positive reaction in the liver an d peripheral blood reticulocytes with almost the same maximum response of micronucleus induction. Our method was found to have the advantage over Cliets' liver micronucleus test in that it required much less ti me and was easier to perform procedures and highly sensitive in detect ing clastogens. It can be used in combination with the peripheral bloo d reticulocyte micronucleus test to evaluate test chemicals in two tis sues, the liver and the bone marrow, in the same animal. We propose a method of combining this test with the peripheral blood reticulocyte m icronucleus test for efficient screening for the clastogenic potential of new chemicals in vivo.