Prolactin (PRL) is a single chain polypeptide hormone which is secreted by the anterior cells of the pituitary gland. The control of prolactin secretion is regulated by the hypothalamus through the release of dopamine (prolactin inhibiting factor), serotonin (prolactin releasing factor) and thyrotropin releasing hormone (TRH). 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.The primary function of prolactin is to stimulate and maintain lactation in women in the postpartum period. Elevated levels may be detected during the eighth week of pregnancy with levels continuing to rise throughout gestation. In the absence of breast feeding prolactin levels return to normal within three weeks of giving birth. Abnormally high levels of prolactin are often associated with female infertility, male impotence and infertility and primary hypothyroidism. The pathological causes of hyper-prolactinaemia include pituitary adenomas (prolactinomas), diseases of the hypothalamus, renal failure, hypothyroidism and ectopic tumours. Prolactin deficiencies in normal individuals however, are rare.
Various drugs are known to either increase of decrease Prolactin levels, for example, L-dopa suppresses the secretion of prolactin and bromocriptine inhibits Prolactin secretion, the latter is therefore used in the treatment of hyper-prolactinaemia. Increased prolactin secretion is seen following the administration of certain drugs, such as phenothiazines (psychotropic drug) and reserpine (anti-hypertensive drug), oestrogen therapy also tends to cause elevated prolactin levels.
Female: 59 – 619IU/mL
Male: 45 – 375 IU/mL
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