VARIABILITY IN D-2-DOPAMINE RECEPTOR DENSITY AND AFFINITY - A PET STUDY WITH [C-11] RACLOPRIDE IN MAN

The variability of D-2-dopamine receptor binding parameters in man was determined using Positron Emission Tomography (PET) and [C-11]raclopr ide. A saturation analysis based on five PET-experiments was performed in each of ten men and ten women. The mean density of D-2-dopamine re ceptors (B-max) was 28 +/- 6.9 pmol/ml (mean +/- S.D.) and the apparen t affinity (K-d(app)) 9.1 +/- 1.9 pmol/ml. The Hill coefficient was in all subjects close to unity (n(H): 0.999 +/- 0.020), thereby indicati ng binding to a homogeneous class of receptors. No significant differe nces between males and females were found in B-max or K-d(app). The in terindividual difference in B-max was statistically significant (alpha = 0.01). The difference in K-d(app) was not significant. Upregulation of the receptor density (B-max) has been widely discussed as a mechan ism for increased dopaminergic neurotransmission in schizophrenia. Thi s study indicates that receptor density varies considerably in a group of healthy subjects. (C) 1995 Wiley-Liss, Inc.