What is prolactin?

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What is prolactin?

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Prolactin is a protein hormone that is secreted from the pituitary gland (at the base of the animals' brain). It is normally found at elevated levels in serum during maintenance of the corpus luteum, at the beginning of the anestrus period, and during early lactation.

What does prolactin do?

Prolactin as it name suggests, it the primary hormone for production of milk from the mammary glands. Prolactin also has effects on the maintenance of the corpus luteum which during pregnancy, helps the mother remain pregnant.

Is prolactin used for any specific tests or treatment during pregnancy?

At this time, no. However, drugs that lower the levels of circulating prolactin have 3 main applications:

1: Terminating an undesirable pregnancy

2: Management of breeding by reducing the duration of diestrus and anestrus

3: Prevention of lactation

There are also a few drugs that mimic the effects of prolactin such as sulpiride and domperidone. They are used when there may be a need to induce lactation such as creating a nurse-maid for a litter of puppies whose mother has just died. They can also be used to help supplement natural lactation in a bitch that was receiving hormones during pregnancy that may have suppressed milk production e.g. progestins.

How are these drugs used?

Anti-prolactin drugs like cabergoline and bromocriptine are actually dopamine antagonists. In the hormonal network of the brain, dopamine and serotonin secreting neurons signal the pituitary to release prolactin. By blocking the effects of dopamine, the levels of prolactin are reduced as well.

After 30 days of gestation, reduction of prolactin can by itself, or in conjunction with other drugs, cause the corpus luteum to regress and end maintenance of pregnancy or terminate diestrus (non-pregnant). Since dogs are completely dependent on functioning corpora lutea to maintain pregnancy, ending the lifespan of the CL's ends the pregnancy or shortens the period of diestrus. These drugs can also be used in late anestrus, to shorten the length of this part of the cycle. Shortening the length of diestrus and anestrus can be desirable to dog breeders, especially if access to a particular male is limited to certain time of year, or if they are trying to produce puppies for availability at a certain time of year.

Interruption of lactation may be necessary in cases such as false pregnancy where the bitch is lactating heavily or in the case of a bitch that lost her puppies soon after birth and is still lactating heavily use of these drugs can help to prevent further medical issues incl. mastitis. There may even be indications for odder medical cases such as lactation secondary to a hormonally active pituitary tumor.

I think my dog may be pregnant. She was bred about 3 weeks ago. Can we start an anti-prolactin drug now to terminate this pregnancy as it is unwanted?

Well, to be perfectly honest. Most reports of bitches being bred are actually false, even when witnessed by an owner. Dogs can mount each other for reasons other than sexual reproduction. A coital tie, with is formed by the dog's penis locking in the vagina of the bitch, usually takes over 30 minutes to subside. Although fertile breedings can take place without a coital tie, one should not assume a fertile breeding based off of a report of dogs mounting for a few minutes. In this case, it would be desirable to confirm pregnancy by ultrasound or other diagnostic test (see what is relaxin) and end the pregnancy with medications only if confirmed. For breedings that took place in a timeframe that is shorter that what can be identified by ultrasound, there are anti-progestin drugs (currently only available outside of the U.S.) that can be used to end the lifespan of the CL's

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