IN-VIVO QUANTIFICATION OF PULMONARY BETA-ADRENOCEPTOR DENSITY IN HUMANS WITH (S)-[C-11]CGP-12177 AND PET

The in vivo regional distribution of pulmonary beta-adrenoceptors was imaged and quantified in humans with the hydrophilic beta-adrenoceptor antagonist (S)-CGP-12177 labeled with carbon-11 {(S)-[C-11]CGP-121771 and positron emission tomography (PET). Six normal male volunteers and eight patients with hypertrophic cardiomyopathy were studied. PET scanning consisted of transmission (tissue density), (CO)-O-15 (blood volume), and (S)-[C-11]CGP-12177 (beta-adrenoceptor) emission scans. High-specific-activity (S)-[C-11]CGP-12177 (7.1 +/- 2.0 mug, 6.5 +/- 2.1 GBq/mumol) was given intravenously followed by a low-specific-activity (S)-[C-11]CGP12177 injection (34.0 +/- 4.8 mug, 2.3 +/- 0.8 GBq/mumol). Binding capacity (Bmax) was calculated in each region of interest as picomoles per gram by normalizing it to the local extravascular tissue density. In normal subjects, average Bmax for all regions of interest was 14.8 +/- 1.6 (SD) pmol/g, which is similar to previously reported in vitro values. In both groups there were no differences in beta-adrenoceptor density between peripheral and central regions nor between right and left lungs. In patients with hypertrophic cardiomyopathy, extravascular tissue density was 24% higher than in normal subjects; Bmax per milliliter thoracic volume was correspondingly higher but was not different from that in normal subjects when expressed per gram tissue (15.8 +/- 2.6 pmol/g). These data suggest that in vivo beta-adrenoceptor density may be quantifiable in humans with the use of PET. This should offer a means to study physiological regulation through repeat measurements.