Breastfeeding: Unraveling the Mysteries of Mother's Milk

, Georgetown University Medical Center

In This Article

Growth Factors and Hormones

The presence of growth factors and hormones in milk and their function has been known for some time (Table VI, VII).[61,62,63,64] Interestingly, the concentration of many growth factors and hormones is higher in a woman's milk than in her plasma. The milk hormones, however, often differ in structure from their maternal serum counterparts, suggesting modification (often post-translational processing such as glycosylation) within the mammary gland. These glycosylated forms often are difficult to detect by standard RIA techniques and have to be quantitated by specific bioassays.[62] The stronger glycosylation protects these bioactive components during passage through the gastrointestinal tract and probably enables the newborn to absorb growth factors and hormones from mother's milk.

It appears that variants of prolactin are present in the circulation of the newborn and that the prolactin acquired from breast milk, and not endogenous prolactin secreted by the newborn's pituitary gland, is essential for the normal development of the neuroendocrine regulation of prolactin in the newborn.[62,65]

Many hormones act in the newborn. While the exact mechanisms of uptake from milk and their mode and site of action in the newborn are known for some, further study is needed to identify these mechanisms for most hormones. Agents in milk seem to stabilize hormones in the gastrointestinal tract of the newborn.

In addition to prolactin, other hormones such as progesterone are present in different form in breast milk than in maternal serum. Transfer of these hormones from milk to infant was documented in some studies directly; in other studies, this transfer is inferred from the documentation of higher serum level of the hormone--for example, thyrotropin releasing hormone (TRH) and somatostatin--in breast-fed than in formula-fed newborns[61]. The milk hormones may also be modified as they pass through the gastrointestinal tract and prior to release into the newborn's blood.


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