Abstract
Summary
The same total dose of 9 mg of N- methylnitrosourea (MNU) was given intrarectally to two groups of ICR/Ha mice by varying the dose rate and frequency. Thirty individual doses of 0.3 mg each three times per week induced large bowel neoplasms with high incidence after the 17th week, compared with six doses of 1.5 mg each three times per week which also led to leukemia in all mice until the 18th week. Small adenomatous nodules of the lung appeared in almost all mice of both groups. In the large intestine, adenocarcinomas and adenomas were found in the distal colon and rectum, and squamous cell carcinomas at the anal canal. Intrarectal instillation of carcinogenic chemicals such as MNU to mice is a good method to develop animal models for colon carcinogenesis, and also other target organs.
We thank Dr. Napoleon E. Magadia, Mr. Ching-Quo Wong, and Miss Alzbeta Hulanova for excellent technical assistance. Also, Dr. Elizabeth K. Weis-burger and Dr. Harry B. Wood, Jr., National Cancer Institute, for providing Af-methylnitrosourea.
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