Prolactin, the milk "let down" hormone-- hyperprolatinemia and pituitaryadenoma.


Lactation is the word used to describe the production of milk from the mammary gland of a mammal. Also called breast-feeding, it is an excellent way to supply a baby with the right nutrition, antibodies, and hydration that evolution has provided for the prolongation of our species. Besides the nutritional benefit, the psychological advantage of bonding is brought to its most loving peak in this beautiful act of nurturing. Sometime in late pregnancy there is a rise of a hormone secreted by cells in the pituitary gland of the brain. Called prolactin.

It is what is termed the "milk let-down hormone." Besides stimulating the milk glands and ducts to manufacture and secrete milk, it also plays a role in blunting the entire menstrual and ovarian cycle so that breast-feeding women are less likely to become pregnant. This is a survival trick of mammals, because the survival of a baby in the past was dependent on not having to compete with a suckling rival.

It is true that some women can become pregnant while breast-feeding, but this only happens if ovulation occurs. The women who get pregnant for some reason overcome the blunting effect of prolactin and make follicles in their ovaries from which they ovulate. An outward sign for a breast-feeding woman is whether she is having regular periods or not while lactating. If she isn't, then she's probably not ovulating regularly and pregnancy is unlikely; if she is, then she's also ovulating regularly and is more likely to conceive.

This blunting of the entire menstrual cycle can be used to a gynecologist's advantage as an important clue. One of the questions we ask when a woman is having only rare periods is whether there is any discharge from her breasts. A bloody discharge, of course, is often but not always a warning signal of cancer.

But white, clear, or milky liquid expressible from the nipple is a sign of lactation.  A drop can be placed on a slide and actually sent in as a Pap smear. Mere lactation will yield a negative Pap.

A woman with sparse periods who can express liquid from her breasts needs a prolactin level, a blood test that can actually tell if too much is being produced. If the prolactin level comes back normal, then this merely means that her breasts are exquisitely sensitive to normal amounts of prolactin. This is innocent, and all that need be done is repeat the prolactin blood test every six months while the patient experiences the nipple discharge. In fact, there used to be an old profession wherein women who continued to lactate long after weaning their own children would actually rent themselves out to women who worked or who had difficulty breast-feeding themselves. Called "Wet Nurses," they would breast-feed under employment. The formula business made them extinct.

Too Much Prolactin

Turning to those women who are lactating because they have too much prolactin, an elevated blood test indicates a problem with the pituitary gland where the prolactin is made. A pituitary adenoma is a benign glandular overgrowth in this gland that cranks out extra prolactin, causing the problem. A woman's periods will be affected, and with this there will be ovulation dysfunction. A high prolactin, called "hyperprolactinemia," will then affect ovulation and cause infertility.

If the gland continues to grow, it can cause problems in the brain. The pituitary gland sits under the brain, over the nose, tucked between the two trunks of the optic nerves as they make their way from the brain to the retina. Although a pituitary adenoma is benign, it can nevertheless cause pressure effects on brain structures as a "space-occupying" lesion.

As it grows it presses on the optic nerve, diminishing vision in those areas of the visual fields supplied by the nerve fibers there. The first visual fields to go will be peripheral vision. A trip to an ophthalmologist is necessary as part of this evaluation. A Magnetic Resonance Imaging (MRI) or CAT scan is used to actually see this benign tumor.

It used to be that neurosurgery was done to remove the adenoma. Because it sat under the brain, the surgical approach was up the nose and through the floor of the skull. (It would be unfeasable to reach it from the top of the head!)This surgery is rare today, because the same medicine used to dry up the breasts after delivery in those choosing to bottle-feed is also used to shrink up a pituitary adenoma. Ironically, this drug is no longer used to dry up the breasts after routine deliveries, because there were reports of severe complications in hypertensive women with it. In our practice we used it to dry up the breasts for over ten years without incident before we stopped prescribing it, as recommended for the FDA..

But it is still a tremendously beneficial drug in women with pituitary adenomas, saving countless neurosurgeries. True, there are those pituitary adenomas that do not respond, but the number of surgeries for this has plummeted.  The blood level of prolactin can be used to judge the success of the treatment (it'll fall).

The endocrine (glandular) system in a woman is an amazing consortium of ups and downs, rises and falls, peaks and troughs, all synchronized to keep the human race going.  As mammals, lactation is a special gift to us, and it is truly ironic that this bodily function otherwise used for nurturing and cuddling can be one of the most dangerous non-malignancies affecting fertility, vision, and even a woman's life.

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