Development of tumours in Syrian hamsters during prolonged experimental exposure to nas.

In several series of experiments, nas was introduced into the buccal pouch or oesophagus of Syrian hamsters or applied to the dorsal skin. In one series, nas was administered to six consecutive generations of hamsters. No tumours appeared at the site of administration, although changes appeared in the mucosa of the buccal pouch and the oesophagus. Tumours in organs remote from the site of application developed only in those series in which nas was introduced into the buccal pouch. The commonest site of tumorigenesis was the liver, followed by the adrenal glands, the forestomach, and the genital organs. Tumours occurred in 17.6% of the experimental animals compared with 3.5% of the controls.

Comparative study of the carcinogenic activities of nas and some chemical carcinogens when introduced into the buccal pouch of the Syrian hamster.

Studies were carried out on the carcinogenic effects of nas, 7,12-dimethylbenz-[a]anthracene (DMBA), DMBA+nas, dimethylnitrosamine (DMNA), diethylnitrosamine (DENA), and N-methyl-N-nitrosourea (MNU) when introduced into the buccal pouch of the Syrian hamster. Nas alone induced no tumours in the buccal pouch but tumours at other sites occurred in 18.8% of the treated animals, compared with 4.4% of the controls. Three of 11 hamsters treated with DMBA alone developed tumours. No tumours appeared in the buccal pouch following treatment with DMBA + nas but they developed at other sites in 6 of the 11 hamsters treated. DMNA and DENA induced no macroscopic changes in the mucous membrane of the buccal pouch. Following DMNA administration, tumours developed only in the liver; no tumours developed following the application of DENA. Tumours developed at various sites, including the buccal pouch, in 20 of the 25 hamsters treated with MNU.