Prolactin

Overview

Prolactin, also known as lactotropin or mammotropin, is a polypeptide hormone secreted primarily by the lactotroph cells of the anterior pituitary gland. It is a monomeric 23 kDa protein, but larger circulating forms exist, such as big prolactin (a dimer) and macroprolactin (big-big prolactin), which are high molecular mass complexes of prolactin and IgG autoantibodies.

It is best known for its role in lactation and breast development, stimulating the growth of mammary alveoli and enabling milk production. Its secretion is primarily regulated by the hypothalamus through dopamine (prolactin-inhibiting hormone), while thyrotropin-releasing hormone (TRH) and suckling act as stimulants.

Beyond reproduction, it also influences maternal and paternal behavior, plays a role in fertility, and is involved in immune regulation, metabolism, and bone health.

Symptoms

Abnormal levels can cause a wide range of symptoms depending on whether levels are elevated (hyperprolactinemia) or reduced (hypoprolactinemia):

1. High Prolactin (Hyperprolactinemia):
   1. In women: Irregular or absent menstrual periods, galactorrhea (milk discharge unrelated to childbirth), infertility, vaginal dryness, painful intercourse, acne, and excessive body or facial hair.
   2. In men: Reduced libido, erectile dysfunction, gynecomastia, infertility, and sometimes osteoporosis.
   3. General symptoms: Headaches and vision problems are associated with pituitary tumors (prolactinomas).
2. Low Prolactin (Hypoprolactinemia):
   1. Insufficient milk production postpartum
   2. Symptoms of pituitary gland dysfunction (e.g., fatigue, loss of secondary sexual characteristics)
   3. Infertility in women and men

Causes

These levels may become abnormal due to physiological, pathological, or pharmacological factors:

1. Causes of Low Prolactin:
   1. Postpartum pituitary necrosis (Sheehan’s syndrome)
   2. Anterior pituitary impairment due to tumors (e.g., craniopharyngioma)
   3. Parasellar diseases or pituitary surgery/radiation, Head injury
   4. Infections (e.g., tuberculosis, histoplasmosis)
   5. Infiltrative diseases (e.g., sarcoidosis, hemochromatosis, lymphocytic hypophysitis)
2. Causes of High Prolactin:
3. Pathological: Pituitary tumors (prolactinoma), hypothyroidism, polycystic ovarian syndrome (PCOS), chronic renal failure, severe liver failure, spinal cord lesions, hypophysitis, or hypophyseal stalk lesions.
   1. Physiological: Pregnancy, breastfeeding, nipple stimulation, exercise, stress, sleep, and seizures.
   2. Pharmacological: Use of dopamine antagonists, monoamine oxidase inhibitors, cimetidine, verapamil, and TRH stimulation tests.

Risk Factors

Several conditions and populations are at greater risk of abnormal levels:

1. Women of Reproductive Age: More prone to hyperprolactinemia due to PCOS, pituitary tumors, or hormonal imbalances.
2. Pregnant and Postpartum Women: Naturally elevated prolactin for lactation; deficiency may impair milk production.
3. Men with Fertility Issues: Low testosterone, erectile dysfunction, or gynecomastia may be linked to prolactin excess.
4. Patients with Thyroid Disorders: Hypothyroidism can increase prolactin secretion.
5. Individuals with Pituitary Tumors: Prolactinomas directly elevate hormone levels.
6. Those Undergoing Long-Term Medication: Drugs that block dopamine or affect hypothalamic regulation raise prolactin levels.
7. Patients with chronic systemic illness, such as chronic renal failure, severe liver disease, or infiltrative conditions, can alter prolactin regulation.

Prevention

While prolactin abnormalities are not always preventable, several strategies help reduce risks and manage conditions effectively:

1. Regular Screening and Monitoring:
   1. Indicated in cases of infertility, irregular menstrual cycles, unexplained galactorrhea, erectile dysfunction, or suspected pituitary tumors.
   2. Normal reference ranges:
      1. Children & Adolescents: 5.0–20.0 ng/mL
      2. Non-pregnant Women: <25.0 ng/mL
      3. Pregnant Women: 80–400 ng/mL
      4. Men: <20.0 ng/mL
2. Laboratory Testing:
   1. Collect 3.0 mL of blood in a plain red-capped tube and separate the serum promptly.
   2. Methods include ELISA and chemiluminescence assays.
3. Lifestyle Measures:
   1. Managing stress and sleep to stabilize prolactin levels.
   2. Avoiding unnecessary medications known to elevate prolactin.
4. Managing Underlying Disorders:
   1. Treat thyroid dysfunction, PCOS, or pituitary conditions promptly.
   2. Address chronic illnesses like renal or liver failure that alter hormone metabolism.
5. Fertility and Lactation Support:
   1. Hormonal therapy may be required for women with recurrent miscarriages, infertility, or inadequate milk production.
   2. Monitoring in postpartum women ensures sufficient prolactin activity for lactation.