Dietary Fat and Mammary Gland Developmental Growth in the Immature Female Mouse

Abstract

The purpose of this study was to determine whether or not the type of dietary fat can affect mammary gland growth processes in the immature female Balb/c mouse. Groups of immature mice were fed one of the following semi-synthetic diets containing different types of fat, i.e., 5 vegetable oil diets (5% corn oil, 20% corn oil, 20% olive oil, 20% linseed oil, 19% coconut oil-1% corn oil), 2 animal fat diets (20% lard, 19% beef tallow-1% corn oil) and 1 fish oil diet (19% Menhaden oil-1% corn oil). In addition, fishcorn oil diets (20%) containing 3 different levels of corn oil (15%, 10%, 4.5%) and fish oil (5%, 10%, 15.5%) were also examined in these studies. Immature mice were fed these diets from 21 to 45 days of age, ovariectomized at 35 days of age, injected daily with 17β-estradiol (1 μg) and progesterone (1 mg) on day 42–44 and sacrificed on day 45. Mammary ductal expansive growth through the mammary fat pad (mm, nipple to farthest end bud) was determined on the inguinal (no. 4) mammary glands. In mice fed the fish oil diets (19% Menhaden oil-1% corn oil, 15.5% Menhaden oil-4.5% corn oil, 10% Menhaden oil-10% corn oil), significantly (P<0.05) reduced ductal expansive growth of the mammary gland was observed when compared to mice fed the 19–20% vegetable oil or animal fat diets. No significant difference in mammary gland growth was observed among the groups of mice fed the 19–20% vegetable oil or animal fat diets. In addition, significantly (P<0.05) reduced mammary gland ductal expansive growth was observed in mice fed the 5% corn oil diet compared to mice fed the 20% corn oil diet. Mean body weight gains among the dietary groups of mice were not significantly influenced by diet. Thus, among the fat diets examined in this study, only the animals fed the low fat diet (5% corn oil) or the fish oil diets (19% Menhaden oil-1% corn oil, 15.5% Menhaden oil-4.5% corn oil, 10% Menhaden oil-10% corn oil) had impaired (reduced) mammae development. The results of our study clearly demonstrate that developmental growth of the mammary gland in immature female mice can be significantly affected (impaired) by diet, but by only rather extreme dietary intervention, i.e., by reducing fat content by 75% (20% to 5%) or by feeding very high levels of certain fish oils (Menhaden) that are extremely rich in n-3 polyunsaturated fatty acids such as EPA and/or DHA.