Prolactin
Why in News?
A study highlighted the link between high prolactin (hyperprolactinemia), recurrent pregnancy loss, and conditions like PCOS/PMOS, bringing attention to prolactin testing in infertility work‑ups.
About Prolactin
- Definition: Prolactin (also called luteotropic hormone or lactogen) is a polypeptide protein hormone mainly responsible for breast development and triggering milk production.
- Origin: It is synthesized and secreted by specialized cells called lactotrophs located in the anterior pituitary gland at the base of the brain.
- Presence: Both men and women have baseline levels of prolactin in their blood, though it is naturally higher in women.
Functions of Prolactin
- Lactation: It initiates and maintains milk synthesis (lactogenesis) in the mammary glands. (Note: It works permissively with oxytocin; prolactin makes the milk, while oxytocin causes milk ejection or let-down).
- Reproductive Regulation: High levels of prolactin act as a temporary, natural contraceptive by suppressing Gonadotropin-Releasing Hormone (GnRH), which subsequently lowers the luteinizing hormone (LH) and follicle-stimulating hormone (FSH) required for ovulation.
- Broader Functions: Beyond reproduction, it plays roles in over 300 separate biological processes, including immune regulation, metabolic homeostasis, and stress responses.
How Prolactin is Controlled?
- Dopamine (The Brake): Unlike most hormones, prolactin is under continuous inhibitory control. The brain chemical dopamine acts as a brake; more dopamine means less prolactin.
- Estrogen (The Accelerator): Estrogen stimulates the pituitary gland to produce more prolactin, which causes levels to spike naturally during pregnancy.
- Thyrotropin-Releasing Hormone (TRH): TRH stimulates prolactin release.
- Diurnal Fluctuations: Prolactin levels are dynamic, naturally peaking during deep sleep and temporary periods of physical stress or strenuous exercise.
Hyperprolactinaemia (High Prolactin Levels)
When prolactin remains abnormally high outside of pregnancy or breastfeeding, it causes several clinical symptoms:
When prolactin remains abnormally high outside of pregnancy or breastfeeding, it causes several clinical symptoms:
- Symptoms in Women: Irregular or entirely absent menstrual cycles (amenorrhea), unexpected milky breast discharge (galactorrhea), vaginal dryness, and difficulty conceiving.
- Symptoms in Men: Decreed testosterone, reduced sex drive (libido), erectile dysfunction, lowered sperm count, and occasionally breast enlargement (gynecomastia).
- Common Causes:
- Prolactinoma: A benign, non-cancerous tumour on the pituitary gland that overproduces the hormone.
- Medications: Anti-dopaminergic drugs (antipsychotics, antidepressants, certain blood pressure or acid reflux medications) that lower dopamine, thereby removing the "brake" on prolactin.
- Medical Conditions: Primary hypothyroidism (underactive thyroid raises TRH, which forces prolactin up), chronic kidney disease, or liver failure.
Diagnosis and Management
- Testing: Diagnosed through a standard serum prolactin blood test. Doctors recommend testing under fasting conditions and resting states to avoid transient spikes caused by stress.
- Imaging: If levels are severely elevated, a brain MRI is used to check the pituitary gland for micro- or macro-prolactinomas.
- Treatment:
- First-line medications: Dopamine agonists such as Cabergoline or Bromocriptine mimic dopamine in the brain to lower prolactin levels and shrink tumours effectively.
- Adjusting Prescriptions: If triggered by a medication, a doctor may adjust or swap the offending pharmaceutical.
