Suitability of CGP-12177 and CGP-26505 for quantitative imaging of β-adrenoceptors

[H-3]GP-12177, a non-selective beta-adrenoceptor antagonist, and [H-3]CGP-26505, a beta-1-selective beta-adrenoceptor antagonist, were intravenously administered to rats. 94-97% of the injected radioactivity disappeared from plasma with t1/2 0.2 and 0.5 min. Total/non-specific binding ratios of 5.4 and 6.9 (CGP-12177) or 2.0 and 2.8 (CGP-26505) were maintained in heart and lung from 10 to 40 min post-injection. Labelled plasma metabolites appeared after > 20 min (CGP-12177) or within 2 min (CGP-26505). No metabolites were found in the heart. CGP-12177 binds to blood cells, but CGP-26505 does not. CGP-12177 can be used for PET imaging of total (beta-1 and beta-2) adrenoceptors in the heart and lung of experimental animals, but CGP-26505 is less suitable for in vivo analysis of the beta-1-subpopulation.