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PRL
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9445
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6
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p
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222-p213
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176760
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5617
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NM_000948
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P01236
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is a
Peptide Hormone synthesised and secreted by
Lactotrope cells in the
Adenohypophysis (anterior
Pituitary Gland ). It is also produced in other tissues including the
Breast and the
Decidua . Pituitary prolactin secretion is regulated by
Neuroendocrine neurons in the
Hypothalamus , most importantly by neurosecretory
Dopamine neurons of the
Arcuate Nucleus , which inhibit prolactin secretion.
Prolactin has many effects, the most important of which is to stimulate the
Mammary Gland s to produce milk (
Lactation ).
Increased serum concentrations of prolactin during
Pregnancy cause enlargement of the
Mammary Gland s of the breasts and increases the production of milk. However, the high levels of
Progesterone during pregnancy act directly on the breasts to stop ejection of milk. It is only when the levels of this hormone fall after childbirth that milk ejection is possible.
Sometimes, newborn babies (males as well as females) secrete a milky substance from their
Nipple s. This substance is commonly known as
Witch's Milk . This is caused by the fetus being affected by prolactin circulating in the mother just before birth, and usually stops soon after birth.
Another effect, recently discovered by the
University Of Paisley and the Technische Hochschule Zürich, is to provide the body with sexual gratification after sexual acts. The
Hormone represses the effect of
Dopamine , which is responsible for sexual arousal, thus causing the male's
Refractory Period . The amount of prolactin can be an indicator for the amount of sexual satisfaction and relaxation. Unusual high amounts are suspected to be responsible for
Impotence .
Other possible functions of prolactin include the
Surfactant synthesis of the fetal lungs at the end of the pregnancy and
Immune tolerance of the fetus by the maternal organism during
Pregnancy .
There is a , lactation will cease within one or two weeks of the end of demand
Breastfeeding . High prolactin levels also tend to suppress the ovulatory cycle by inhibiting the secretion of both
FSH and
GnRH .
Prolactin is a single chain polypeptide of 199
Amino Acid s with a molecular weight of about 24,000
Dalton s. Its structure is similar to that of
Growth Hormone and
Placental Lactogen . The molecule is folded due to the activity of three
Disulfide Bond s. Significant heterogeneity of the molecule has been described, thus bioassays and immunoassays can give different results due to differing glycosylation, phosphorylation, sulfation, as well as degradation. The non-glycosylated form of prolactin is the dominant form of prolactin that is secreted by the pituitary gland.
is apparently the result of removal of some amino acids, while '''big prolactin''' can be the product of interaction of several prolactin molecules.
Pit-1 is a
Transcription Factor that binds to the prolactin gene at several sites to allow for the production of prolactin in the pituitary gland. A key regulator of prolactin production are
Estrogen s that enhances growth of prolactin producing cells and stimulates prolactin production directly as well as suppressing
Dopamine .
The - encoded by a gene on Chromosome 5p13-14 - interacts with the prolactin molecule as a
Transmembrane Receptor . Thus it contains an extracellular region that binds prolactin, a transmembrane regions, and a cytoplasmatic region. A specific
Second Messenger has not yet been identified. There may be variations among different tissue prolactin receptors.
Prolactin levels may be checked as part of a sex hormone workup, as elevated prolactin secretion can suppress the secretion of FSH and GnRH, leading to
Hypogonadism , and sometimes causing
Erectile Dysfunction in men.
Prolactin levels may be of some use in distinguishing
Epileptic Seizures from
Psychogenic Non-epileptic Seizures .
Hyperprolactinaemia is the term given to having too-high levels of prolactin in the blood.
As a
Contraceptive , demand breastfeeding is said to be more than 90% effective in the first month of post-partum even if no other forms of contraception are used, with decreasing effectiveness in successive months. This effect is said to be responsible for the natural spacing of children seen in countries where contraception is not widely available, and is thought to be an evolutionary means of ensuring adequate care is provided to each newborn. The 90% effectiveness only applies if three criteria are met:
- 1. The mother has no periods at all ( Amenorrhea )
- 2. The baby is exclusively breast-fed
- 3. It is six months or less since birth.
If one or more of these conditions are broken, fertility returns to normal. It is not advised, however, to rely on this method as the only contraceptive for any long period of time.
- Speroff L, Glass RH, Kase NG. Clinical Gynecologic Endocrinology and Infertility. Sixth edition. Lippincott Williams & Wilkins, Baltimore, MD 1999. ISNB 0-683-30379-1.
