Angiotensin 1 is a decapeptide (ten amino acids), which is converted to angiotensin 2 (eight amino acids). The latter has more hypertensive effect and also stimulates the release of aldosterone from adrenal gland. Methionine enkephalin is a pentapeptide found in brain.

Functions: It has opiate-like function and inhibits the sense of pain. Bradykinin and kallidin are mono and decapeptides.