Variability in D2-dopamine receptor density and affinity: a PET study with [11C]raclopride in man.

The variability of D2-dopamine receptor binding parameters in man was determined using Positron Emission Tomography (PET) and [11C]raclopride. A saturation analysis based on five PET-experiments was performed in each of ten men and ten women. The mean density of D2-dopamine receptors (Bmax) was 28 +/- 6.9 pmol/ml (mean +/- S.D.) and the apparent affinity (Kdapp) 9.1 +/- 1.9 pmol/ml. The Hill coefficient was in all subjects close to unity (nH: 0.999 +/- 0.020), thereby indicating binding to a homogeneous class of receptors. No significant differences between males and females were found in Bmax or Kdapp. The interindividual difference in Bmax was statistically significant (alpha = 0.01). The difference in Kdapp was not significant. Upregulation of the receptor density (Bmax) has been widely discussed as a mechanism for increased dopaminergic neurotransmission in schizophrenia. This study indicates that receptor density varies considerably in a group of healthy subjects.