Influence of the type of dietary fat on developmental growth of the mammary gland in immature and mature female BALB/c mice.

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 and mature female BALB/c mouse. Groups of immature and mature mice were fed one of the following purified semisynthetic diets containing different types of fat, i.e., five vegetable oil diets (5% corn oil, 20% corn oil, 20% olive oil, 20% linseed oil, 19% coconut oil-1% corn oil); two animal fat diets (20% lard, 19% beef tallow-1% corn oil); and one fish oil diet (19% Menhaden oil-1% corn oil). In addition, fish-corn oil diets (20%) containing three 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, given injections daily of 17 beta-estradiol (1 microgram) and progesterone (1 mg) on Days 42 to 44, and sacrificed on Day 45. Mammary ductal expansion through the mammary fat-pad (mm, nipple to farthest end bud) was determined on the inguinal (No. 4) mammary glands. Mature mice were fed these diets from 28 to 128 days of age. Half of these mice were sacrificed between 118 and 128 days of age during the stage of estrus of the estrous cycle. The remaining half were given injections daily of 17 beta-estradiol (1 microgram) and progesterone (1 mg) from 118 to 127 days of age and sacrificed on Day 128. Mammary developmental growth was assessed on inguinal mammary glands by ascription of development scores, determination of epithelial area (mm2), and determination of total DNA levels. In both immature mice and mammotrophic hormone-treated mature mice fed the fish oil diet (19% Menhaden oil-1% corn oil, 15.5% Menhaden oil-4.5% corn oil), significantly (P less than 0.05) reduced developmental growth of the mammary gland was observed when compared to mice fed the 19 to 20% vegetable oil or animal fat diets. No significant difference in mammary gland developmental growth was observed among the groups of mice fed the 19 to 20% vegetable oil or animal fat diets. In immature mice and mammotrophic hormone-treated mature mice, significantly (P less than 0.05) reduced mammary gland developmental growth was observed in mice fed the 5% corn oil diet compared with mice fed the 20% corn oil diet. In mature mice not treated with exogenous mammotrophic hormones, no significant effect of diet on mammae development was observed.(ABSTRACT TRUNCATED AT 400 WORDS)