FAILURE OF HIGH-FAT DIETS TO PROMOTE MAMMARY CANCERS IN SPONTANEOUSLYHYPERTENSIVE RATS

Rat strains differ in their susceptibilities to chemically-induced mam mary carcinogenesis. The present study tested the hypothesis that the spontaneously hypertensive rat (SHR) strain is resistant to mammary ca rcinogenesis. Resistance would imply the presence of the mammary carci noma suppressor (MCS) gene. Therefore, we also wanted to test the abil ity of this gene to inhibit mammary tumor promotion in the presence of high fat diets. Female SHRs were treated with DMBA (5 mg/rat) at 50 d ays of age and transferred to either a 20% corn oil or 19% menhaden oi l + 1% corn oil diet one week later. At 17 weeks post-DMBA none of the rats in either group developed mammary carcinomas. Multiple palpable nodules formed in the mammary gland indicating that initiation had occ urred. We conclude that the SHR strain is genetically resistant to DMB A-induced mammary carcinogenesis by mechanisms involving a blockade of promotion.