- Prolactin (PRL) is a peptide hormone secreted by anterior pituitary and is critical for lactation and breast development in women.
- Regulatory Axis
- Prolactin is synthesized and secreted by lactotrophs of the anterior pituitary. Synthesis and secretion of pituitary PRL is under control of the hypothalamus via releasing and inhibitory hormones. Hypothalamic TRH acts as the releasing hormone whereas hypothalamic dopamine acts as an inhibitory hormone, although inhibition by dopamine is likely the dominant control mechanism. Additionally, prolactin secretion appears to be under negative feedback control as high levels of prolactin induce hypothalamic secretion of dopamine.
- Prolactin is only found at significant levels in pregnant or lactating women. During pregnancy, the levels of PRL steadily increase, reaching a peak immediately before delivery. Following birth of the child, PRL levels decline to their low, pre-pregnancy levels; however, they then display rapid peaks whenever suckling at the nipple occurs.
- Breast Development: Together with estrogen and progesterone, prolactin induces proliferation and growth of mammary glands during puberty and again during pregnancy.
- Lactation: Prolactin stimulates mammary glands to synthesize milk.
- Inhibition of ovulation: Prolactin inhibits hypothalamic release of GnRH, resulting in decreased ovulation. This explains why breast-feeding tends to promote reversible infertility.
- Prolactin deficiency results in defective lactation during pregnancy. Prolactin deficiency may arise within a context of generalized hypopituitarism especially when Sheehan Syndrome is the etiology.