Kathryn is pregnant and very eager to breast-feed after the baby is born. Her friend gives her a supplement to encourage prolactin secretion and Kathryn starts to take it during pregnancy. The supplement works and Kathryn's blood level of prolactin increases. She does not begin lactating during pregnancy because
A. maternal plasma levels of prolactin are low during pregnancy.
B. the high levels of estrogen and progesterone in maternal plasma inhibit the effects of prolactin.
C. the breast ducts do not develop until after parturition.
D. the low levels of circulating estrogen and progesterone during pregnancy inhibit milk synthesis by the breasts.
E. high levels of androgens inhibit milk synthesis by the breasts.
Answer: B
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