Physiology, Prolactin

Excerpt

Prolactin is a polypeptide hormone responsible for lactation, breast development, and hundreds of other actions needed to maintain homeostasis. The chemical structure of prolactin is similar to the structure of growth and placental lactogen hormones. Together, they form the "prolactin/growth hormone/placental lactogen" family, which is characterized by a conserved helix bundle protein composition. All hormones in this family derive from a common ancestral gene.

Prolactin is composed of 199 amino acids after the proteolytic cleavage of the signal peptide from the prolactin prohormone (pre-prolactin) and posttranslationally modified. It is common knowledge that the anterior pituitary synthesizes and secretes prolactin and dopamine-mediated hypothalamic regulation; however, the central nervous system, the immune system, the uterus, and the mammary glands are all capable of producing prolactin. Nipple stimulation, light, olfaction, and stress can all contribute to the initiation of prolactin synthesis in these tissues. Other factors that stimulate prolactin production include thyrotropin-releasing hormone (TRH), estrogen (pregnancy), and dopamine antagonists (antipsychotics). Males have characteristically low levels of prolactin. Abnormal elevation in males is suggestive of a potential underlying pathological process like a pituitary adenoma or a medication adverse effect, which warrants further evaluation. Prolactin is low in males and non-lactating non-pregnant females.