Endocrinology of lactation.

Hormones are necessary for the growth of mammary glands, for initiation of the secretory process, and for the maintenance of an established lactation in all mammals. Hormonal changes which occur in late pregnancy and the early postpartum period are described and graphed. This data was derived from research with animal models and relevant human data. Enzymatic and cytologic differentiation of the mammary gland and limited mammary secretion begin during late pregnancy. This constitutes the 1st stage of lactogenesis. The 2nd stage consists of a great increase in lactation secretion occurring 0-4 days before delivery. Quantities of milk produced are very variable. The role of all the following hormones in lactogenesis are described: prolactin; adrenocorticotropin (ACTH, which stimulates glucocorticoid secretion); estrogens; placental lactogens. Maintenance of intense lactation also depends on a complex of hormones. Prolactin seems to be the most important hormone at this stage of the process. Milk secretion continuation is reliant on constant milk removal.