Prolactin, Serum

Prolactin is a polypeptide hormone secreted by the anterior pituitary gland. While best known for its role in lactation, prolactin also modulates immune function, reproductive physiology, and dopaminergic tone. It is clinically relevant in the evaluation of amenorrhea, galactorrhea, infertility, and suspected pituitary pathology.

Elevated prolactin (hyperprolactinemia) suppresses gonadotropin-releasing hormone (GnRH), which in turn reduces LH and FSH output — leading to hypogonadism, menstrual irregularity, or infertility. Markedly elevated prolactin (>200 ng/mL) raises suspicion for prolactinoma (pituitary adenoma). Mild elevations can result from medications (antipsychotics, SSRIs), stress, or nipple stimulation.

Prolactin is elevated by dopamine antagonism and by certain anabolic compounds, particularly those in the 19-nortestosterone family, which have progestogenic activity that stimulates prolactin release. In the context of hormonal assessment, prolactin provides information about pituitary function and dopaminergic regulation that complements gonadotropin (LH/FSH) and testosterone measurement.