What is the effect of estrogen on prolactin during pregnancy?

• A. Estrogen inhibits prolactin release from the anterior pituitary
• B. Estrogen stimulates prolactin release
• C. Estrogen has no effect on prolactin
• D. Estrogen eliminates prolactin production

Answer: (A)

Estrogen during pregnancy helps prepare the breasts for lactation but keeps milk production from starting. It does this, in part, by inhibiting prolactin release from the anterior pituitary. That inhibition prevents milk secretion while the breasts are developing and the placenta is supplying high levels of estrogen and progesterone. After delivery, estrogen (and progesterone) levels fall, the inhibitory environment is removed, and prolactin can act to stimulate milk production in response to infant nursing. This is why pregnancy shows breast development with no milk production yet, and lactation begins postpartum when the hormonal blockade is lifted.