Variability in D2‐dopamine receptor density and affinity: A PET study with [11C]raclopride in man

Abstract

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 (B_max) was 28 ± 6.9 pmol/ml (mean ± S.D.) and the apparent 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 indicating binding to a homogeneous class of receptors. No significant differences between males and females were found in B_max or K_d^app. The interindividual difference in B_maxwas statistically significant (α = 0.01). The difference in K_d^app was not significant. Upregulation of the receptor density (B_max) 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.