Prolactin

from Wikipedia, the free encyclopedia
Prolactin
Prolactin
Ribbon representation according to PDB  1N9D

Existing structural data : 1n9d , 1rw5 , 2q98 , 3d48

Properties of human protein
Mass / length primary structure 198 AS ; 22.9  kDa
Identifier
Gene name PRL
External IDs
Occurrence
Homology family Prolactin
Parent taxon Vertebrates

Prolactin or prolactin ( PRL ), also called lactotropic hormone ( LTH ), lactotropin or lactotropin , is a hormone that is produced in the lactotropic cells (acidophilic, approx. 20% of the adenohypophysis) in the anterior pituitary gland and primarily for the growth of the mammary gland is responsible during pregnancy and for milk secretion ( lactation ) during breastfeeding , and also has psychological functions. In the bitch , prolactin is responsible for maintaining the corpus luteum in the second half of the cycle (also during pregnancy) .

structure

The primary structure of human prolactin consists of 198 amino acids with a molecular mass of 22892 Daltons . The tertiary structure of the polypeptide is determined by three disulfide bridges . There is a structural similarity to somatotropin .

The gene locus is on chromosome 6 .

function

This hormone stimulates the growth and differentiation of the mammary gland during pregnancy and leads to milk production (lactation) in mammals during lactation . Prolactin also suppresses follicle rupture (ovulation), as the pulsatile (but not basal) release of the gonadotropins ( LH and FSH ) necessary for this is inhibited. In humans, this contraceptive effect ( lactation menorrhea method ) , which has only been researched in more detail since the 1990s, depends on the duration and frequency of breastfeeding.

Prolactin triggers brood care behavior in all mammal species examined so far, as well as in many other vertebrates , both in females and in males if they are involved in brood care. In humans, too, shortly before the birth of the child, an increase in the prolactin level of the pregnant woman's partner can be observed, albeit a significantly lower one than in the mother.

In the European eel ( Anguilla anguilla ), the prolactin regulates a change in the gill epithelium . As a result, the eel adapts to the different osmotic environments of the seawater or freshwater during its catadromic migration (see also readiness to act ).

production

The release of prolactin is regulated by messenger substances from the hypothalamus and occurs in a (not very pronounced) circadian day-night rhythm, increasingly during the second half of the night. The release of prolactin is subject to a complex interplay of several factors, with inhibition by the neurotransmitter dopamine (= prolactostatin) being an essential control mechanism. For this reason, dopamine agonists (e.g. ergot alkaloids ) are used as the agent of choice for prolactin-producing tumors (see below), as they not only lower the prolactin concentration in the blood serum , but usually also significantly reduce the tumor size. In contrast to dopamine, other hypothalamic factors have a stimulating effect on prolactin release, such as TRH , VIP , angiotensin II , endogenous opioids , oxytocin and the hypothetical prolactin-releasing hormone ( PRH ), the presence of which, however, has not yet been proven. To date, however, no hormone has been discovered whose primary effect is to stimulate prolactin release. The PRH is therefore only a hypothesis. Furthermore, the release is promoted by stress , non-REM sleep and hypoglycaemia . This is of practical importance insofar as an increased prolactin concentration in the blood (e.g. in the context of a pronounced hypothyroidism ) can prevent or delay ovulation (see above).

The ambient temperature also has a significant influence on the prolactin level. This increases with increasing temperature, while it decreases with decreasing temperature. However, the ambient humidity has no effect.

Overproduction

An increased prolactin level often leads to the absence of ovulation and the absence of menstruation in women. When milk flow or disorders of the menstrual cycle in a woman who does not breastfeed, the Prolaktinwert should be determined. Before each operation on a tumor of the pituitary gland , the prolactin level is determined to determine whether it is a prolactinoma . In the case of prolactinomas, drug therapy is often successful and surgery is superfluous.

A continuously increased prolactin value indicates various disorders and diseases. It is known as hyperprolactinemia . In (adult) men, the normal value (♂) for prolactin is below 15 ng / ml.

  • Normal value (♀): 2–25 ng / ml
  • Gray area (♀): 25–200 ng / ml
  • clearly pathological :> 200 ng / ml

A prolactin value in the gray range (25–200 ng / ml) is determined during the breastfeeding phase, with hypothyroidism , when taking various medications (especially neuroleptics such as amisulpride and risperidone or drugs such as cannabis ), with neurogenic (e.g. safely increased after epileptic seizures ) and psychiatric disorders, irritation of the thoracic nerves, e.g. B. Herpes zoster , endometriosis , acute and chronic physical and psychological stressful situations , during pregnancy , after an orgasm, after intensive manipulation of the breast, after protein-rich food and high beer consumption.

If the value exceeds 200 ng / ml, a tumor of the pituitary gland (prolactinoma) can be assumed. A prolactinoma can lead to secondary hypogonadism because high levels of prolactin disrupt the pulsating secretion of the sex hormones LH and FSH .

As part of breast cancer treatment , a low prolactin levels is desirable since prolactin can promote tumor growth.

Individual evidence

  1. ↑ UniProt P01236
  2. ↑ Klinke, Pape, Silbernagl (ed.): Physiology . 5th edition. Thieme, Stuttgart 2005, ISBN 3-13-796005-3 , p. 533 .
  3. ↑ Ludvik, Kraupp, Luger (Ed.): Endocrinology and Metabolism . 4th edition. Facultas.wuv, Vienna 2010, ISBN 978-3-7089-0537-2 , p. 83 f .
  4. ↑ Silbernagl, Lang (ed.): Pocket Atlas of Pathophysiology . 2nd Edition. Thieme, Stuttgart 2005, ISBN 978-3-13-102192-2 , p. 260 .
  5. ↑ H. Schmidt-Mathiessen, P.-H. Althoff, B. Barde, H. Becker, JSE Dericks-Tan, E. Jungmann, DK Lüdecke, W. Saeger, Kv Werder: Hyperprolactinemia - Prolactinomas: Physiology - Clinic - Therapy . Ed .: Ortrun Jürgensen. Springer-Verlag, Heidelberg 2013, ISBN 978-3-642-73609-4 , p. 69 .

Web links