This is a hormone produced by the anterior pituitary gland. Prolactin is a polypeptide hormone composed of 199 amino acid residues.
Synthesis:
- synthesised by cells of the pituitary (lactotrophs)
- only small amounts of prolactin are stored in the pituitary gland
Release:
- under inhibitory dopaminergic control and stimulatory thyroid releasing hormone (TRH) control
- increased release at night
- in females - increased release during puberty
- androgens may have a modest inhibitory effect on release
- released in response to stress e.g. exercise
- prolactin levels are high during pregnancy - oestrogen causes an increase in numbers of lactotrophs
- during lactation, suckling of the breast results in an increased release of prolactin
Actions:
- breast - milk protein synthesis and excretion in ducts and lobules
- contraceptive effect - seen with high levels of prolactin
- has no established function in males
What level of prolactin is significant?(1)
- mildly increased prolactin levels (400-600mu/L) may be physiological and asymptomatic but higher levels are usually pathological
- very elevated levels (above 5,000mu/L) usually imply a prolactin-secreting pituitary tumour
Note that reference ranges vary between laboratories.
Notes:
- prolactin secretion varies with time, resulting in serum levels being 2-3 times higher at night than during the day. The levels of prolactin in normal individuals also tend to rise in response to physiological stimuli, including sleep, exercise, pregnancy and surgical stress (2)
- most patients with a prolactinoma are women
Reference: