Effects of high dietary fat on the total DNA and receptor contents in rats with 7,12-dimethylbenz[a]anthracene-induced mammary carcinoma

The influence of high dietary fat on the malignant intensity and the hormone receptors of 7,12-dimethylbenz[a]anthracene (DMBA)-induced mammary carcinoma in female Sprague-Dawley rats were analyzed by the tumor incidence and growth, the DNA histogram type, the DNA index, the S-phase fraction, and the estrogen receptor (ER) and progesterone receptor (PgR) assays. The rats were fed either a low-fat (0.5% corn oil) diet or a high-fat (20% corn oil) diet after the DMBA administration. Tumor incidences in the low-fat and the high-fat diet groups were 46 and 86%, respectively (p less than 0.01). Tumors in the high-fat diet group were also significantly larger than those in the low-fat group. Average tumor latent period was significantly shorter in the high-fat diet group, comparing with that in the low-fat diet group (p less than 0.01). Sixty-nine percent of the tumors in the high-fat diet group had aneuploid type, while only 8% of those in the low-fat diet group had aneuploid type. The DNA index and S-phase fraction also were significantly higher in the high-fat diet group (p less than 0.01). But the ER and PgR contents were not different between both groups. Therefore, these results suggest that a high dietary fat could increase the malignant intensity of the tumor but does not influence the hormonal responsiveness of these tumors.