Expansion
GnRH, TRH, CRH and GHRH stimulate; dopamine and somatostatin inhibit
Expansion
| Hypothalamic factor | Pituitary effect |
|---|---|
| GnRH | Stimulates LH and FSH |
| TRH | Stimulates TSH (and prolactin) |
| CRH | Stimulates ACTH |
| GHRH | Stimulates growth hormone |
| Somatostatin | Inhibits growth hormone and TSH |
| Dopamine | Inhibits prolactin |
They reach the anterior pituitary through the hypophyseal portal system, a rare example of a portal circulation, allowing tiny quantities to act without systemic dilution.
Two clinically exploited quirks:
- Pulsatility: GnRH given in pulses stimulates, but given continuously it downregulates receptors and suppresses gonadotrophins. This is why GnRH agonists such as goserelin are used to induce chemical castration in prostate cancer, after an initial testosterone flare
- Dopamine inhibition of prolactin: dopamine agonists (cabergoline, bromocriptine) treat prolactinoma, while dopamine antagonists (antipsychotics, metoclopramide) cause hyperprolactinaemia with galactorrhoea and amenorrhoea
Somatostatin analogues such as octreotide treat acromegaly and neuroendocrine tumours.