GLOSSARY

Amine hormones are small hormones derived from a single amino acid (mainly tyrosine or tryptophan); despite their shared chemical origin, they behave differently, some acting like peptides (water-soluble) and others like steroids (fat-soluble).

Types

• Catecholamines (from tyrosine): adrenaline, noradrenaline, and dopamine; water-soluble, with membrane receptors (GPCRs), a very short half-life (about 1–2 minutes), and storage in vesicles.
• Thyroid hormones (from two tyrosines plus iodine): T4 and T3; fat-soluble, with nuclear receptors, bound to carrier proteins, and a long half-life (T4 about 7 days).
• Melatonin (from tryptophan): from the pineal gland; membrane receptors (MT1 and MT2); regulates circadian rhythm.
• Serotonin (from tryptophan): mainly a neurotransmitter and paracrine signal (about 90 percent in the gut).

The Catecholamine Synthesis Pathway