Hyperprolactinemia is an inevitable consequence of treatment with
antipsychotic agents to some extent because
prolactin response to
antipsychotics is related to
dopamine blockade. Recent studies have suggested that polymorphisms of the
dopamine receptors are associated with therapeutic response to
antipsychotics. Thus, we studied the effects of major polymorphisms of
dopamine-related genes on plasma concentration of
prolactin. Subjects were 174 schizophrenic patients (68 males, 106 females) receiving 3 mg twice daily of
risperidone for at least 4 weeks. Sample collections were conducted 12 h after the bedtime dosing. Five
dopamine-related polymorphisms (Taq1A, -141C ins/del for DRD2, Ser9Gly for DRD3, 48 bp VNTR for DRD4, Val158Met for COMT) were identified. The mean (+/-SD) plasma concentration of
prolactin in females was significantly higher than males (54.3+/-27.2 ng/ml versus 126.8+/-70.2 ng/ml, p<0.001). No
dopamine-related polymorphisms differed the plasma concentration of
prolactin in males or females. Multiple regression analyses including plasma drug concentration and age revealed that plasma concentration of
prolactin correlated with gender (standardized partial correlation coefficients (beta)=0.551, p<0.001) and negatively with age (standardized beta=-0.202, p<0.01). No correlations were found between
prolactin concentration and
dopamine-related polymorphisms. These findings suggest that plasma
prolactin concentrations in females are much higher than in males but the
dopamine-related variants are not predominantly associated with plasma concentration of
prolactin.