SIMULTANEOUS EVALUATION BY A DOUBLE LABELING METHOD OF DRUG-INDUCED UPTAKE INHIBITION AND RELEASE OF DOPAMINE IN SYNAPTOSOMAL PREPARATION OF RAT STRIATUM

Crude synaptosomal preparations from corpora striata of rat were preloaded with [14C]DA [dopamine], rinsed and then incubated with [3H]DA and the drug to be tested. During the 5 min of the second incubation, DA uptake and release rates were time- and temperature-dependent. On this double labeling test, nomifensine, cocaine, benztropine and amphetamines displayed IC50 [median inhibitory concentration] and release curves similar to those obtained from separate uptake and release studies. In the presence of high concentrations of iprindole, amitriptyline and butriptyline (> 3 .times. 10-6 M), a [14C]DA release was observed which closely coincided with an apparent inhibition of [3H]DA uptake. This double labeling test allows the determination of the participation of the releasing effect of drugs in their apparent inhibition of DA uptake.