Prolactin

PRL acts to initiate and maintain milk secretion by the mammary glands. It works with other hormones such as oxytocin, which actually causes milk ejection, and oestradiol, progesterone, glucocorticoids, GH, thyroxine and insulin, which prepare the mammary gland for milk production. Other functions are unclear but experimental animals have been shown to produce PRL in response to stress. PRL may also play a part in fertility and maternal behaviour. PRL secretion is under inhibitory control of dopamine. This means that if the link between the hypothalamus and pituitary is severed PRL secretion increases, unlike all other pituitary hormones, where production would decrease without stimulatory control of the hypothalamus. TSH has a stimulatory affect on PRL secretion. Oestradiol increases PRL production and levels of PRL rise during pregnancy and remain high during lactation.

What can go wrong

PRL secreting tumours are a very common type of pituitary tumour. The high levels of PRL lead to loss of reproductive function and inappropriate milk production (galactorrhoea) in males and females although male symptoms are often less obvious. Treatment is with the dopamine agonist bromocriptine. Undersecretion of PRL is very rare and does not have any clinical symptoms.