What Is Prolactin and Why Does It Disrupt Male Sexual Function?

We frankly do not know why men have prolactin-producing capability at all. Prolactin serves an important function in women, but only at a specific moment in their reproductive lives. At the end of a woman’s pregnancy, her pituitary produces and releases generous amounts of prolactin into the bloodstream to stimulate breast-milk production. Nursing mothers usually have no menstrual periods because prolactin levels, when elevated, extinguish the pulses of pituitary hormones required to activate the normal menstrual cycle. When a woman stops nursing, prolactin levels decrease, pulsatile pituitary hormone secretion resumes, and menstrual function returns.

How does this relate to impotence in men? The same hormonal events that cause hyperprolactinernic women to stop menstruating while they are nursing also causes hyperprolactinemic men to become impotent.

Elevated serum prolactin levels create two problems that are inimical to sexual potency. With high serum prolactin levels, normal pulsatile GnRH and LH secretion does not proceed. This is why nursing mothers stop menstruating. Without pulsatile LH release, a man’s testicle is stranded without adequate stimulation and cannot produce its full ration of testosterone. Serum testosterone levels then fall. But giving more testosterone is not the remedy because elevated serum prolactin levels also prevent the body from responding normally to testosterone.

Two treatments — one surgical, the other medical — curtail excessive prolactin secretion by the pituitary.

Surgical removal of the prolactin-secreting pituitary tumor eliminates the source of excessive prolactin. Unfortunately, excision of only the pituitary tumor, while desirable, is not always feasible. Whittling away at the pituitary mass does make a significant dent in prolactin secretion but rarely decreases it to the normal range. In these cases, impotence persists.

Doctors have discovered that a chemical in the body called dopamine normally reins in pituitary prolactin secretion in men. Without dopamine, prolactin levels increase. A selective doparnine deficiency in the hypothalamus is therefore presumed to be responsible for hyperprolactinernia in men. By restoring dopamine levels to normal, pituitary prolactin production is suppressed.

Three medications, bromocriptine (Parlodel), pergolide (Permax), and cabergoline (Dostinex) have doparninelike properties, and any of them can

be an effective dopamine surrogate. When hyperprolactinemic men or women are treated with bromocriptine (Parlodel), pergolide (Permax) or cabergoline (Dostinex), serum prolactin levels promptly return to normal. Continued treatment is required to keep prolactin levels fully suppressed.

This treatment has been effective in two respects. Lowering serum prolactin levels to normal restores sensitivity to the sexual effects of testosterone. As serum prolactin levels fall, serum testosterone levels increase and potency returns. Bromocriptine (Parlodel) or cabergoline (Dostinex) treatment also decreases pituitary tumor size and shrinks prolactin-secreting tumor tissue.

In some impotent hyperprolactinernic men, bromocriptine (Parlodel) or cabergoline (Dostinex) treatment alone suffices. Men with recent onset of impotence and small pituitary tumors are more likely to respond. Other men, especially those with large pituitary tumors, are not able to revitalize their own testosterone-producing capability without the additional help of testosterone injections or patches. Once serum prolactin levels are normalized, these impotent men regain their responsiveness to the sexually stimulating effects of testosterone.

Vincent was forty-one, weak, fatigued, impotent, about to lose his business and maybe his wife. His doctor noted that Vincent had unusually low blood pressure and small testicles. X-rays disclosed an enlarged pituitary, and blood tests established that — as a consequence of inadequate stimulation from his pituitary — adrenal, thyroid, and testicular hormone production were subnormal. Treatment with adrenal and thyroid hormones so invigorated Vincent that he was able to return to work, and his business prospered. Testosterone injections normalized serum testosterone levels, but he remained impotent. Ordinarily, testosterone-deficient men experience a brisk increase in sexual desire and potency with testosterone therapy. Treatment failures occur in men who have, in addition to their testosterone deficiency, other problems such as neuropathy, vascular disease, depression, or hyperprolactinemia. In Vincent’s case, hyperprolactinemia was the culprit. His large pituitary gland, incapable of supporting function of his adrenal, thyroid, or testicle, was not totally inert, for it continued to produce prolactin in exorbitant amounts. Only when bromocriptine treatment normalized serum prolactin levels were testosterone injections effective in restoring Vincent’s sexual drive and potency.

Bromocriptine was the treatment of choice once it was established that Vincent’s sexual problems were linked with his high serum prolactin level. At that time, bromocriptine was the only medication available to normalize his serum prolactin level.

Subsequently another prolactin-lowering medication, pergolide (Permax), was made available. Both bromocriptine and pergolide will lower prolactin production, but to be effective, they must be taken every day. Cabergoline (Dostinex) also lowers prolactin production but differs from bromocriptine and pergolide because of its long duration of action. Taken once a week, or at most twice weekly, cabergoline is all that is needed to normalize serum prolactin and testosterone levels in the majority of hyperprolactinemic men and women.

Pituitary tumors are not the only causes of hyperprolactinemia. Many drugs used to treat high blood pressure, emotional problems, and gastric problems can compromise the action of doparnine and allow prolactin levels to increase. These problem drugs include reserpine (Serpasil), methyldopa (Aldomet), chlorpromazine (Thorazine), trifluoperazine (Stelazine), thioridazine (Mellaril), haloperidol (Haldol), prochlorperazine (Compazine), and metoclopramide (Reglan).

One Response to “What Is Prolactin and Why Does It Disrupt Male Sexual Function?”

  1. Joseph says:

    I am taking Dostinex for prolactinoma. Can you please tell me at what level prolactin suppresses testosterone? I’m attempting to get an idea of when my testosterone level may begin to return to normal. My prolactin level started out at 125 times normal and is down to 7 times normal, but testosterone is not rising.

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