INDUCTION OF TUMOURS IN RAT BY A SINGLE ORAL DOSE OF N-NITROSOMETHYLUREA

N-methyl-N-nitrosourea was given in a single intragastric dose of 90 mg./kg. body wt to three groups of young Wistar rats, since previous biochemical experiments had led to the prediction that this dose would produce a high incidence of tumours of the kidney. Rats from the first group were kept until they died or were obviously ill. Thirty-one survived more than 1 month. Tumours were found in the kidney (15), small intestine (6), large intestine (16), jaw (odontoma) (2), and skin (keratoacanthoma) (8). In the squamous stomach, tumours greater than 3 mm. diameter were found in nine rats; in 15 other animals numerous small white nodules were found on the squamous mucosa. The microscopic appearance of the tumours is described. Rats from the second experiment were killed in groups of four at intervals from 6 to 29 weeks after the dose. The first tumours of the stomach and small intestine were found 10 weeks after the dose. Tumours of the large intestine, skin and kidney were found 20 weeks after the dose. Rats killed at intervals between 2 hours and 3 weeks after the dose showed pathological change particularly in the thymus, lymph nodes and bone marow. There was a marked reduction of all cell types in the bone marrow and an acute leucopoenia persisted for 2 weeks after the dose. The results of a general histological survey are reported. We are very grateful to Dr. W. H. Butler and Dr. B. Terracini for their advice on the classification of some of the pathological specimens, and to Mr. I. F. Gaunt, B.Sc., M.I. Biol., of the British Industrial Biological Research Association, for the blood and marrow counts, and Mr. R. F. Legg, A.I.M.L.T., who prepared the photomicrographs. © 1969, The British Empire Cancer Campaign for Research. All rights reserved.