PRL

Prolactin (PRL), also known as luteotropic hormone or luteotropin, is a protein that is best known for its role in enabling mammals, usually females, to produce milk. It is secreted by the pituitary gland on the instruction of chemical signals from the hypothalamus. Prolactin plays an essential role in metabolism, regulation of the immune system, and pancreatic development.

Overview

Prolactin is a peptide hormone primarily associated with lactation. In females, high circulating levels after childbirth trigger milk production. However, prolactin is not exclusive to females or lactation; it is found in males and non-lactating females in smaller amounts and has various functions in the body, including a role in the immune response and as a regulator of behavior and reproductive physiology.

Structure and Function

Prolactin is a single-chain protein hormone closely related to growth hormone and placental lactogen. It is synthesized and secreted by lactotroph cells in the anterior pituitary gland. Its secretion is regulated by the hypothalamus, primarily through the inhibitory hormone dopamine. Factors such as emotional stress, pregnancy, and physical stimulation of the breasts can influence prolactin release.

Effects

Beyond its primary role in lactation, prolactin has over 300 functions in the body. It affects water and electrolyte balance, helps regulate the immune system, and supports the development of the pancreas. In some species, prolactin is involved in parental behaviors, such as nesting and care of the young.

Clinical Significance

1. 1. 1. Hyperprolactinemia

An excess of prolactin, known as hyperprolactinemia, can lead to a variety of symptoms. In women, it may cause galactorrhea (production and spontaneous flow of breast milk), amenorrhea (absence of menstrual periods), and infertility. In men, high levels of prolactin can lead to erectile dysfunction, decreased libido, and infertility. Hyperprolactinemia can be caused by various factors, including pituitary tumors (prolactinomas), certain medications, and thyroid disease.

1. 1. 1. Hypoprolactinemia

Conversely, low levels of prolactin, or hypoprolactinemia, are less common and less understood. It can be associated with inadequate milk production in postpartum women.

Diagnosis and Treatment

Diagnosis of prolactin disorders typically involves blood tests to measure the hormone's levels, alongside imaging studies like MRI to identify potential pituitary tumors. Treatment depends on the underlying cause. Dopamine agonists are commonly used to treat hyperprolactinemia by inhibiting prolactin secretion. In cases of prolactinoma, surgery or radiation therapy may be necessary.

Conclusion

Prolactin is a versatile hormone with key roles in reproduction, lactation, and overall health. While often associated with pregnancy and breastfeeding, its influence extends to many areas of physiology and behavior. Understanding prolactin's functions and how to manage its disorders is crucial for reproductive health and beyond.