Endocrinology of reproduction half of pregnancy, progesterone and prolactin prepare the mammary glands for lactation. Estrogens and progesterone promote mammary epithelial cell proliferation resulting in the formation of the primary and secondary ductal structure. Progesterone induces formation of tertiary side-branches in the mammary glands during puberty and during the luteal phase of the menstrual cycle upon which lobuloalveolar structures form under the influence of prolactin. Prolactin stimulates lactogenesis. hCG appears to be soporific during pregnancy; levels of hCG correlate with sleep changes during pregnancy, and administration of hCG increases sleep in rats likely via neuronal LHCGR. Endocrinology of reproduction Hormonal regulation occurs at
Breast development the breasts by inducing the expression of the progesterone receptor (PR) in breast epithelial tissue. In contrast to the case of the PR, ER expression in the breast is stable and differs relatively little in the contexts of reproductive status, stage of the menstrual cycle, or exogenous hormonal therapy. During pregnancy, pronounced breast growth and maturation occurs in preparation of lactation and breastfeeding. Estrogen and progesterone levels increase dramatically, reaching levels by late pregnancy that are several hundred-fold higher than usual menstrual cycle levels. Estrogen and progesterone cause the secretion of high levels of prolactin from the anterior pituitary, which