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Prolactin has a wide variety of effects. It stimulates the mammary glands to produce milk (): increased serum concentrations of prolactin during pregnancy cause enlargement of the mammary glands and prepare for milk production, which normally starts when levels of progesterone fall by the end of pregnancy and a suckling stimulus is present.
The release of prolactin triggers the cells in the alveoli to make milk. Prolactin also transfers to the breast milk. Some research indicates that prolactin in milk is greater at times of higher milk production, and lower when breasts are fuller, and that the highest levels tend to occur between 2 a.m. and 6 a.m. [7]
Hyperprolactinemia, characterized by abnormally high levels of prolactin, may cause galactorrhea (production and spontaneous flow of breast milk), infertility, and menstrual disruptions in women. In men, it can lead to hypogonadism, infertility and erectile dysfunction. Prolactin is crucial for milk production during pregnancy and lactation.
Prolactin gene transcription is responsible for the production of prolactin. Prolactin is involved in the maturation of mammary glands and their secretion of milk in association with oxytocin, estrogen, progesterone, glucocorticoids, and others. Prolactin has numerous other effects in both sexes. [3]
Prolactin, produced in the anterior lobe of the pituitary gland, is the major hormone responsible for milk production.During pregnancy, the level of prolactin rises to trigger the development of mammary tissue in the breast to prepare it for milk supply. [17]
With suckling from the infant, prolactin and oxytocin are secreted and mediate milk production and letdown, respectively. [20] [21] [29] Prolactin suppresses the secretion of LH and FSH, which in turn results in continued low levels of estrogen and progesterone, and temporary amenorrhea (absence of menstrual cycles) occurs. [29]
High levels of prolactin are necessary for lactation, however there is no direct correlation between baseline levels of prolactin and quantity of milk production. [5] One aspect of supply regulation that has been identified is that breast milk contains a peptide called feedback inhibitor of lactation (FIL).
By the twentieth week of gestation, mammary glands have reached a sufficient level of development to generate milk components as a result of stimulation by prolactin. [33] Post-lactational involution refers to the process of breast tissue returning to its normal state after milk production stops due to a decrease in prolactin levels. [33]