Observations on Leukemia in Wistar and Wistar Furth Rats

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

2. Among 303 autopsied animals there were 403 benign and malignanttumors, 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 apparentlydecreased 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 ratleukemia are discussed in this article, and the possible significance of theappearance and disappearance of the distinctive mononuclear cells in theperipheral blood is pointed out.

6. Pathologic findings indicate that the majority of deaths, other than thosedue to leukemia, were due to pulmonary infections and a great variety oftumors. 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 leukemiasin Wistar rats green chloromatous tissues were found in 5 animals.

7. Cytogenetic studies were carried out on direct preparations from thebone marrow in most of the leukemic rats in this series. Aneuploidy wasnoted in several animals and one W/Fu rat demonstrated a morphologicallyabnormal "marker" chromosome. In more recent studies improved technicsand use of the spleen as a source of metaphase preparations have affordedbetter opportunities to obtain adequate chromosome preparations in leukemic rats. Further investigations are in progress and special studies arebeing directed to the viral and cytogenetic aspects of leukemia in the rat.

Submitted on December 4, 1964 Accepted on January 25, 1965