Neuropeptides
Short peptides that set physiology and behavior from the brain outward.
oxytocin · vasopressin · CRH · TRH
Overview
The posterior pituitary releases two closely related nonapeptides — oxytocin and vasopressin (ADH) — synthesized in the hypothalamus and differing by only two amino acids, yet governing very different physiology: social bonding and parturition versus water retention and vascular tone.
The hypothalamic releasing hormones — CRH, TRH, GnRH — sit at the top of the major endocrine axes, each triggering a specific anterior-pituitary output (ACTH, TSH, and the gonadotropins respectively).
Neuropeptides illustrate how small sequence differences and receptor distribution, not size, encode specificity — a recurring theme across the peptide-hormone system.
Key signals
Parturition, lactation, and social/affiliative behavior.
Also called ADH; renal water retention and vasoconstriction; osmotic control.
Apex of the HPA stress axis; drives pituitary ACTH release.
Drives pituitary TSH release; sets thyroid-axis tone.
Reference notes
- Oxytocin and vasopressin differ by two residues yet act on distinct receptor families — a textbook case of sequence-level specificity.
- Releasing hormones are pulsatile; continuous (non-pulsatile) exposure can desensitize the downstream axis (notably GnRH).
- Central versus peripheral receptor distribution explains why these peptides have both behavioral and physiological roles.