Prolactin
Prolactin (PRL) is a 199-amino-acid peptide hormone secreted by lactotroph cells of the anterior pituitary gland. It is named for its primary role in lactation, but has remarkably diverse functions across reproduction, immune modulation, metabolism, and social behavior.
Regulation: Dopamine as the Key Inhibitor
Unlike most anterior pituitary hormones, prolactin is tonically inhibited by the hypothalamus rather than stimulated:
- Dopamine (from hypothalamic tuberoinfundibular neurons) → D2 receptors on lactotrophs → inhibits prolactin release
- TRH (thyrotropin-releasing hormone) → stimulates prolactin release
- Suckling stimulus → afferent neural signals → suppresses dopamine → prolactin surge
- Estrogen → sensitizes lactotrophs and reduces dopaminergic inhibition
This dopamine–prolactin axis explains why dopamine antagonists (antipsychotics such as haloperidol, risperidone, and others) cause hyperprolactinemia as a major side effect.
Primary Role: Lactation
Prolactin drives milk production (lactogenesis):
- During pregnancy, prolactin levels rise steadily, but milk production is blocked by high progesterone and estrogen.
- After delivery, progesterone and estrogen fall → prolactin action on mammary glands is no longer blocked → milk synthesis begins.
- Suckling maintains prolactin secretion: each nursing episode causes a prolactin spike, sustaining lactation.
- Prolactin also suppresses GnRH/LHRH → suppresses ovulation → lactational amenorrhea (natural post-partum infertility).
Secondary Roles
Immune modulation:
- Prolactin receptors (PRLR) are expressed on T-cells, B-cells, and NK cells
- Prolactin promotes lymphocyte proliferation and cytokine production
- Has been proposed as a link between psychological stress and immune function
Social bonding and parental behavior:
- Prolactin rises in fathers after interacting with newborns — cross-species finding in mammals and birds
- In pair-bonding species, prolactin promotes affiliative behavior and parental care
- Elevated prolactin in both parents correlates with investment in offspring
- Linked to dopamine reward circuits: high prolactin may damp dopaminergic reward for new sexual partners, reinforcing pair-bond fidelity
Other roles: Regulates water/salt balance, promotes immune tolerance of fetus during pregnancy, modulates pain perception.
Hyperprolactinemia
Elevated prolactin is one of the most common endocrine disorders. Causes:
| Cause | Mechanism |
|---|---|
| Dopamine antagonist drugs | Antipsychotics, metoclopramide (antiemetic), domperidone |
| Prolactinoma | Benign pituitary tumor (most common pituitary adenoma) |
| Hypothyroidism | Elevated TRH → stimulates prolactin |
| Pregnancy/breastfeeding | Normal physiological rise |
| Nipple stimulation/stress | Reflex rise |
Symptoms of hyperprolactinemia:
- In women: galactorrhea (spontaneous milk), amenorrhea, infertility, low libido
- In men: hypogonadism, low testosterone, erectile dysfunction, gynecomastia
Treatment: Dopamine agonists (cabergoline, bromocriptine) — directly suppress prolactin production by activating D2 receptors on lactotrophs. Highly effective; most prolactinomas regress without surgery.
Prolactin and Antipsychotics
Second-generation (“atypical”) antipsychotics vary in D2 blockade strength → variable prolactin elevation:
- High elevation: risperidone, paliperidone, haloperidol
- Moderate: amisulpride
- Low/none: clozapine, quetiapine, aripiprazole (D2 partial agonist → actually lowers prolactin)
Monitoring prolactin is important in long-term antipsychotic treatment, especially in young patients (bone density, reproductive health).
see also
Tags: HormoneNeurotransmitter science ai-generated
Superlink: 052 🫧Hormone und Neurotransmitter
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Erstellt: 01-09-22 11:14