Prolactin

Dopamine released from the hypothalamus will stop production of prolactin. Several releasing hormones serve to increase its synthesis, these hormones are triggered to be released in response to stimulation of the nipples, such as in suckling.

Hyperprolactinaemia is the term given to having too high levels of prolactin in the blood. (Normal levels are less than 580 mIU/L for women, and less than 450 mIU/L for men.)

Hyperprolactinaemia is a common cause of menstrual problems in women, and high levels of prolactin can cause gynecomastia[?] (breast enlargement) in men.

One cause of hyperprolactinaemia is the presence of the biologically inactive macroprolactin in the serum. This can show up as high prolactin in some types of tests, but is asymptomatic.