Observations on Leukemia in Wistar and Wistar Furth Rats

1. Six-hundred and seventy-three Wistar and W/Fu rats were treated at the age of 4 months with whole body x-ray, orally administered 3MCA or a combination of these agents. All animals were followed until death and 87 per cent were autopsied.

2. Among 303 autopsied animals there were 403 benign and malignant tumors, including 28 leukemias.

3. Differences were noted in the incidence and types of leukemia occurring in both breeds of rats. In Wistars 9 of 11 leukemias were myelogenous and 8 of these followed x-ray exposure.

4. Approximately a 10 per cent incidence of spontaneously occurring mononuclear cell leukemia was found in W/Fu rats; exposure to x-ray apparently decreased the occurrence of leukemia in these rodents. Following oral administration of 3MCA, 13 per cent of W/Fu rats developed acute mononuclear cell leukemia.

5. Results of hematologic, cytologic and histochemical studies on rat leukemia are discussed in this article, and the possible significance of the appearance and disappearance of the distinctive mononuclear cells in the peripheral blood is pointed out.

6. Pathologic findings indicate that the majority of deaths, other than those due to leukemia, were due to pulmonary infections and a great variety of tumors. In leukemic animals enlargement of the spleen was almost universally present and adenopathy, especially involving mediastinal and retroperitoneal glands, was frequently noted. Among 9 myelogenous leukemias in Wistar rats green chloromatous tissues were found in 5 animals.

7. Cytogenetic studies were carried out on direct preparations from the bone marrow in most of the leukemic rats in this series. Aneuploidy was noted in several animals and one W/Fu rat demonstrated a morphologically abnormal "marker" chromosome. In more recent studies improved technics and use of the spleen as a source of metaphase preparations have afforded better opportunities to obtain adequate chromosome preparations in leukemic rats. Further investigations are in progress and special studies are being directed to the viral and cytogenetic aspects of leukemia in the rat.