prolactin

Examples of prolactin in the following topics:

• Physiology of Lactation

  • This stage requires prolactin and oxytocin.
  • At birth, prolactin levels remain high, while the delivery of the placenta results in a sudden drop in progesterone, estrogen, and human placental lactogen levels.
  • This abrupt withdrawal of progesterone in the presence of high prolactin levels stimulates the copious milk production of the lactogenesis II stage.
  • When the breast is stimulated, prolactin levels in the blood rise, peak in about 45 minutes, and return to the pre-breastfeeding state about three hours later.
  • The release of prolactin triggers the cells in the alveoli to make milk.

• Hormonal Regulation of the Reproductive System

  • In addition to producing FSH and LH, the anterior portion of the pituitary gland also produces the hormone prolactin (PRL) in females.
  • Prolactin stimulates the production of milk by the mammary glands, following childbirth.
  • Prolactin levels are regulated by the hypothalamic hormones, prolactin-releasing hormone (PRH) and prolactin-inhibiting hormone (PIH) (which is now known to be dopamine).
  • PRH stimulates the release of prolactin, while PIH inhibits it.

• Mammary Glands

  • Secretory alveoli develop mainly in pregnancy, when rising levels of prolactin, estrogen, and progesterone cause further branching, together with an increase in adipose tissue and a richer blood flow.
  • Milk secretion (lactation) begins a few days later due to reduction in circulating progesterone and the presence of prolactin, which mediates further alveologenesis, milk protein production, and regulates osmotic balance and tight junction function.
  • Their binding ensures correct placement of prolactin receptors on basal lateral side of alveoli cells and directional secretion of milk into lactiferous ducts.
  • During weaning, decreased prolactin, missing mechanical stimulation (baby suckling), and changes in osmotic balance caused by milk stasis and leaking of tight junctions cause cessation of milk production.

• Pituitary Gland Disorders

  • The hypothalamus secretes a number of hormones, often according to a circadian rhythm, into blood vessels that supply the anterior pituitary; most of these are stimulatory (thyrotropin-releasing hormone, corticotropin-releasing hormone, gonadotropin-releasing hormone and growth hormone-releasing hormone), apart from dopamine, which suppresses prolactin production.
  • In response to the releasing hormone rate, the anterior pituitary produces its hormones (TSH, ACTH, LH, FSH, GH) that stimulate effector hormone glands in the body, although prolactin acts directly on the breast gland.
  • Measurement of ACTH and growth hormone usually requires dynamic testing, whereas the other hormones (LH/FSH, prolactin, TSH) can typically be tested with basal levels.

• Overview of the Pituitary Gland

• Phenylketonuria (PKU)

  • Low levels of dopamine lead to high levels of prolactin.
  • By contrast, in classic PKU, prolactin levels would be relatively normal.

• The Anterior Pituitary

  • For example, a prolactinoma is a pituitary adenoma that overproduces prolactin.
  • Prolactin, known as PRL, is a polypeptide hormone whose target is the ovaries and mammary glands.

• Freshwater Environments

  • The eel (Anguilla anguilla) uses the hormone prolactin, while in salmon (Salmo salar) the hormone cortisol plays a key role during this process.

• Labor and Birth

  • When the baby begins suckling at the breast, signals are sent to the hypothalamus causing the release of prolactin from the anterior pituitary, which signals the mammary glands to produce milk.

• Fibrocystic Disease of the Breasts

  • The most important of these hormones are estrogen, progesterone, and prolactin.