Prolactin

Prolactin is a hormone produced by the anterior pituitary in pregnancy, sleep, lactation, stress, physical exercise and hypoglycaemia. It stimulates the growth of glandular tissue in the breast and is necessary to produce milk. Prolactin inhibits FSH and LH.

Dopamine usually inhibits the secretion of prolactin. TRH stimulates the production of prolactin.

Pathologically elevated prolactin is called hyperprolactinaemia, and decreased prolactin is called hypoprolactinaemia.

Hyperprolactinaemia

Hyperprolactinaemia is the increased production of prolactin. It's a relatively rare disorder. Not all cases are patholohical, as it can occur physiologically in case of pregnancy, nipple stimulation, and stress.

Etiology

Pathological hyperprolactinaemia occurs in:

Prolactinoma (most common cause)
Damage to the hypothalamus or infundibulum
Hypothyroidism
Dopamine antagonist drugs (like antipsychotics and certain antiemetics)
Chronic kidney disease – due to decreased excretion

A prolactinoma is a prolactin-producing pituitary adenoma. Damage to the hypothalamus or infundibulum impairs the dopamine-mediated inhibition of prolactin. TRH stimulates prolactin, and so prolactin may be elevated in severe hypothyroidism. Dopamine antagonist drugs inhibit the dopamine D2 receptor, thereby inhibiting dopamine's inhibitory effects on prolactin secretion.

Pathophysiology

As the level of prolactin is pathologically high the synthesis of dopamine is increased to attempt to inhibit prolactin synthesis. This is not sufficient or able to reduce the prolactin level back to normal. As a side effect of the increased dopamine synthesis, dopamine will suppress the production of GnRH, which decreases LH and FSH, which decreases androgen and oestrogen production.

Clinical features

The most common symptoms of hyperprolactinaemia are:

Decreased gonadotropic effects
- Hypogonadism
- Amenorrhoea
- Infertility
- Gynaecomastia
- Decreased libido
Galactorrhoea – non-physiological milk discharge
Bilateral hemianopsia – if caused by a tumor which compresses the optic chiasm

Management

The treatment of choice is dopamine agonists and treating the underlying cause.