Lack of effect of dietary fat on the growth and estrogen sensitivity of the MT‐W9B transplantable mammary tumor

Abstract

The growth rate and the estrogen responsiveness of the MT‐W9B transplantable mammary tumor were examined in female Wistar‐Furth rats which were fed diets containing either 0.5% or 20% fat for 50–60 days. Estrogen responsiveness was determined by changes in progesterone receptor concentration in response to estrogen deprivation and replacement. This parameter was also measured in the uterus as a normal tissue control. Progesterone receptor levels in tumor and uterus were reduced by ovariectomy to a similar extent in rats fed either low‐ or high‐fat diets. In addition, estrogen induction of the progesterone receptor in ovariectomized rats was not altered by dietary fat intake. Growth of the MT‐W9B tumor was not affected by either diet or endocrine manipulation. Uterine growth, as expected, was dependent on estrogen status, but both the growth and its sensitivity to estrogen manipulation were independent of the fat content of the diet. These data suggest that dietary fat does not influence the sensitivity of normal or neoplastic tissue to estrogen action.