Visualization of beta-Adrenoceptors Using PET.
PET-investigations of beta-adrenoceptors in heart, lungs, and brain are of great clinical interest. Receptor densities are altered under various pathophysiological conditions. This review gives an overview of PET-research of beta-adrenoceptors. The clinical relevance of in vivo PET-investigations of beta-adrenoceptors is described for heart, lungs, and brain. Results obtained with the available PET-ligands are discussed. [(11)C]CGP 12177 has been successfully applied in patients with cardiac and pulmonary diseases. The complicated labelling procedure prevents widespread use of the radiopharmaceutical. Due to its lipophilicity, [(18)F]-fluorocarazolol is a suitable ligand for cardiac and pulmonary as well as for cerebral sites. Non-specific binding is higher as compared to [(11)C]CGP 12177. Unfavorable toxicity data prevents human use of this ligand. [(11)C]Carazolol shows comparable distribution in heart and lung as [(18)F]fluorocarazolol, but it hardly enters the brain. [(11)C]CGP 12388 displays comparable pharmacokinetics in rats and is much easier prepared than [(11)C]CGP 12177. Therefore [(11)C]CGP 12388 seems a promising PET-ligand for clinical studies of cardiac and pulmonary beta-adrenoceptors. Pilot studies with the long-acting agonist [(11)C]formoterol have indicated that it may be possible to investigate the high affinity state of the beta(2)-subtype.