Differences in DMBA-induced mammary neoplastic responses in two lines of Sprague-Dawley rats

Abstract

It has been reported that female Sprague-Dawley rats obtained from a U.S. source and studied in the U.S. gave a larger and more rapid mammary neoplastic response to radiation than did female Sprague-Dawley rats obtained from a Dutch source and studied in The Netherlands. To learn if the different mammary neoplastic responses of the two ‘lines’ of Sprague-Dawley rats are due to inherent differences between the lines of rats or due to differences in experimental conditions, two groups of rats from the American source and one group from the Dutch source were studied for their response to a chemical carcinogen, dimethylbenzanthracene (DMBA), at the same laboratory. When 10 mg of DMBA per 100 g body wt was given by stomach tube to 28 rats from the Dutch source, 367 days later approximately 25% of these rats had developed mammary carcinomas and approximately 18% had developed mammary fibroadenomas. When the same dose of DMBA was given to rats from the U.S. source, 300 days later 90 and 100% had developed mammary carcinomas and 83 and 95% had developed mammary fibroadenomas. Similar trends were found for the number of neoplasms per rat and the mean time of appearance of the neoplasms. It was concluded that there are inherent differences between Sprague-Dawley rats obtained in the U.S. and Sprague-Dawley rats obtained in The Netherlands in regard to their mammary neoplastic responses to DMBA, as well as in their responses to radiation. Genetic differences between the two lines were confirmed by establishing dissimilarities in the expression of erythrocyte antigens coded for by RT1 (major histocompatibility complex).