Class A. Rhodopsin family

   Biogenic amine [Fig]

   Neuropeptide

   Cardiovascular peptide

   Pituitary hormone

   Hypothalamic hormone

   Pancreatic peptide

   Gut peptide

   Complement peptide

   Chemokine

   Base and nucleoside

   Lipid

   Vision

   Chemoreception

     Olfactory

   Other

 Class B. Secretin receptor family

 Class C. Metabotropic glutamate receptor family

 Others