Prolactin is 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.
Hyperprolactinaemia may be physiological in the situations described above, but it may also be pathological. Pathological hyperprolactinaemia occurs in:
- Prolactinomas – prolactin-producing pituitary adenomas – most common cause
- Damage to the hypothalamus and infundibular stalk – as this impairs the dopamine-mediated inhibition of prolactin
- Hypothyroidism – as TRH stimulates prolactin
- Dopamine antagonists
- Chronic renal failure – due to decreased excretion
The most common symptoms of hyperprolactinaemia are:
- Decreased gonadotropic effects
- Decreased libido
- Galactorrhoea – non-physiological milk discharge
- Bilateral hemianopsia – if caused by a tumor which compresses the optic chiasm
The cause of the decreased gonadotropic effects should be explained. As the level of prolactin is high will the body try to counteract this by producing more dopamine, which usually suppresses prolactin production. Dopamine fails to do this however, but it does suppress the production of GnRH, which decreases LH and FSH, which decreases testosterone and oestrogen production.
The treatment of choice is dopamine agonists and treating the underlying cause.
55. Disorders of the hypothalamo-pituitary system. Pituitary insufficiency
57. Pathophysiology of growth