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Prolactin

Prolactin is one of the many hormones produced and secreted by the pituitary gland in the brain, it can also be produced in the adipose (fat) cells, uterus, and breast tissues. The homeostasis of prolactin is dependent on two hormones; dopamine which inhibits its synthesis in the pituitary gland, and estrogen which promotes it.
Prolactin’s function is involved in a variety of processes in both men and women, but its effects are more dominant in women; its main function is to promote lactation during nursing. Excess of prolactin causes detrimental effects, and it is important to diagnose and address hyperprolactinemia.

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Healthy prolactin levels

The normal range of prolactin levels can vary depending on the lab kits but generally is < 25 ng/ml in adult women, and it increases in pregnancy to reach between 34 and 386 ng/ml with the highest peak being during labor then gradually goes back to normal around 6 weeks after delivery. Prolactin levels in men are lower, usually less than 15 ng/ml.

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Implications of high prolactin levels

Concentrations of prolactin in the blood may increase due to different factors, but most commonly due to a dysfunction in its production and secretion at the pituitary level.

Non-pituitary causes include antipsychotic treatment (e.g., haloperidol, risperidone, olanzapine, phenothiazines) which have been well evidenced to do so. Some antidepressants have also been reported to be culprits (e.g., citalopram, paroxetine, or fluoxetine) but no conclusion can be fully drawn from the studies so close monitoring may be suggested on an individual basis.

Another cause could be hypothyroidism, as a high concentration of thyroid-releasing hormone enhances the secretion of prolactin. Hormonal contraceptives are also known to cause hyperprolactinemia due to high estrogen levels.

The main reason for hyperprolactinemia is due to a disorder in the anterior pituitary gland where prolactin is synthesized and secreted. This is a prolactinoma, a benign tumor in the pituitary gland that causes an unhinged excess production of prolactin leading to increased blood concentrations. The tumor is non-cancerous and is treated with conventional therapy and not chemotherapy. In extreme, resistant cases surgery or radiotherapy may be needed.
Prolactinoma occurs in men and women, but more regularly in women younger than the age of 50. The disease is non-hereditary, meaning there is no family history involved.

Symptoms of high prolactin levels

To gauge the importance of treatment, one should know what the side effects of high prolactin levels are. For example, more generally, the increased size of the pituitary gland in prolactinoma may compress surrounding tissues in the brain causing headaches and blurry vision. More symptoms of hyperprolactinemia are going to be sex and age dependent.

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Women younger than 50 years old, or those who have not reached menopause yet, will have a variety of symptoms related to high concentrations that all can be traced back to how prolactin affects the normal functioning of the ovaries. Prolactin interferes in the ovarian production of hormones such as estrogens and progesterone. Its surplus will cause a decrease in estradiol leading to:
Disruption in menstruation, sometimes halting them (referred to as amenorrhea)
Infertility due to anovulation
Menopausal symptoms like decreased libido and vaginal abnormalities
Milk discharge even when not nursing (referred to as galactorrhea)
Secondary hormonal changes like acne and hirsutism
Osteoporosis if left untreated for a long time.

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Women who have already gone through menopause will not experience any manifestations until late as the disease progresses without treatment.
Men are affected differently, for example, they will not experience infertility despite prolactin disrupting the normal function of the testes. Hyperprolactinemia will cause a decrease in testosterone production and a disturbance in sperm development, leading to:
Decreased energy levels.
Decreased libido.
Weakened muscle mass.
Gynecomastia
Osteoporosis if left untreated for a long time.

Dopamine Agonists

They are the first-line treatment and include two agents: Bromocriptine and Cabergoline. They act by increasing dopamine concentration which inhibits the production and secretion of prolactin in the anterior pituitary gland. Bromocriptine follows a daily regimen, to be taken with food to minimize gastrointestinal side effects.

Hormonal therapy in women

As mentioned, hyperprolactinemia causes a decrease in estradiol which drags on the various ailments. Supplementing with estrogen and progesterone therapy may be an option in women who cannot tolerate dopamine agonist treatment for whatever reason.

Professional procedures

Surgery and radiation therapy are options in cases where prolactinoma is resistant to dopamine agonist treatment, or when there is a relapse after discontinuation of treatment. Both interventions aim to reduce the size of the pituitary gland which will reduce production and secretion. Radiation may be less effective because it takes time to see effects and is often a second choice after surgery.

Conclusion

Prolactin is a crucial hormone in the well-being of the reproductive system as it affects both ovarian and testicular functions. Hyperprolactinemia can be due to either a benign tumor in the pituitary gland known as prolactinoma or due to different treatments. It is not a life-threatening condition but still requires medical attention due to its effect on the quality of life.
How to reduce prolactin is fairly straightforward. The majority of patients respond well to dopamine agonist regimens which can be employed across a variety of patients. Women who are on these therapies and plan on getting pregnant are advised to discontinue treatment before pregnancy, and if the prolactinoma is not yet resolved, they are referred to surgery as an ultimate option to reduce high prolactin levels.