Exposure to flaxseed or its lignan component during different developmental stages influences rat mammary gland structures.

Reduction of the highly proliferative terminal end bud (TEB) structures in the developing mammary gland by differentiation to alveolar buds (ABs) and lobules has been suggested to be protective against mammary cancer. Flaxseed is high in alpha-linolenic acid (ALA) and secoisolariciresinol diglycoside (SDG). SDG is the precursor of mammalian lignans, which can affect mammary gland structures. Thus, the objective of this study was to determine the effect of lifetime, gestation and lactation or after-weaning exposure to 5 or 10% flaxseed or SDG and flaxseed oil components on the mammary gland structures of virgin female rat offspring at post-natal day 50. Lifetime or gestation and lactation exposure to flaxseed altered mammary gland structure development, whereas exposure to flaxseed after weaning had no effect. Lifetime or gestation and lactation exposure to 5% flaxseed caused endocrine changes, as suggested by delayed puberty onset and reduced number of estrous cycles. These changes reduced exposure to endogenous estrogens, leading to atrophy of mammary TEB structures. SDG, but not flaxseed oil, at the level found in 5% flaxseed produced similar effects as 5% flaxseed. This suggested that the lignans were the component in flaxseed responsible for the observed effects. Lifetime or gestation and lactation exposure to 10% flaxseed also caused endocrine changes, as suggested by early puberty onset and lengthened cycles due to prolonged estrus. This increased exposure to endogenous estrogens and stimulated mammary gland differentiation, as indicated by fewer TEBs and more ABs. Thus, lifetime or gestation and lactation exposure to 5 or 10% flaxseed induced structural changes in the mammary gland that may potentially reduce mammary cancer risk.