- polypeptide hormone 9 amino acids
- first peptide hormone to be sequenced and synthesized (1953).
- single gene arose by duplication of vasopressin gene
- vasopressin is 9 amino acid hormone constricts blood vessels and retain body water.
- hormone degraded by GIT.
- hormone cannot pass the blood-brain barrier.
- Birth - increase in uterine muscle tone and strength of contractions.
- Lactation - hormone released in response to the baby suckling.
- stimulates contraction of muscle cells around mammary glands.
- neural effects