Chronic treatment with SCH 23390, a selective dopamine D-1 receptor antagonist, decreases dopamine metabolism in rat caudate nucleus.

Chronic treatment (18 days; 0.1 and 0.5 mg/kg per day) with the selective dopamine (DA) D-1 receptor antagonist, SCH 23390, significantly reduced the concentration of homovanillic acid (HVA) and the ratios of HVA/DA and DOPAC/DA in the nucleus caudatus of the rat but did not change the metabolism of DA in the prefrontal cortex, substantia nigra or the A10 area. Furthermore, the concentrations of noradrenaline were dose dependently decreased in the A10 area during SCH 23390 treatment. It is concluded that chronic DA D-1 receptor blockade causes changes in the metabolism of DA similar to those caused by classical neuroleptics.