Dopamine (prolactin-inhibiting hormone)
Also known as: dopamine, PIH, prolactin-inhibiting factor, tuberoinfundibular dopamine
Dopamine released from tuberoinfundibular neurons into portal blood is the physiological prolactin-inhibiting hormone, holding lactotrophs under constant tonic inhibition.
Overview
Unlike every other anterior pituitary hormone, prolactin is controlled mainly by inhibition. Dopaminergic neurons of the arcuate nucleus (the tuberoinfundibular or A12 group) release dopamine at the median eminence into the portal capillaries. On lactotrophs it binds D2 receptors (Gi-coupled), lowering cAMP, opening K⁺ channels and closing Ca²⁺ channels, which suppresses prolactin secretion, prolactin gene transcription and lactotroph proliferation. Dopamine also mildly inhibits TSH secretion.
Prolactin itself stimulates these dopamine neurons (short-loop feedback). During suckling, afferent nerve signals inhibit tuberoinfundibular dopamine release, allowing a prolactin surge.
- Location
Source: arcuate nucleus (tuberoinfundibular dopaminergic neurons) → median eminence. Target: lactotrophs (D2 receptors).
Function
- Tonically inhibits prolactin secretion and lactotroph growth.
- Mildly inhibits TSH secretion.
- Physiology
Class: catecholamine (amine derived from tyrosine). Receptor: D2 (Gi → ↓cAMP).
- Regulation
Stimulated by prolactin (short-loop feedback); inhibited by suckling, estrogen and stress.
Clinical significance
Drug-induced hyperprolactinaemia
D2 antagonists — antipsychotics (risperidone, haloperidol), antiemetics (metoclopramide, domperidone) — and dopamine-depleting drugs (methyldopa, reserpine) raise prolactin, causing galactorrhoea, amenorrhoea, gynaecomastia and erectile dysfunction.
Dopamine agonist therapy
Cabergoline and bromocriptine shrink prolactinomas and normalise prolactin in most patients; they are first-line therapy even for large tumours. They are also used to suppress lactation.
Compiled from standard anatomy and physiology references — see the Endocrine System sources. For education only; not medical advice.