[H-3]Pramipexole: a selective radioligand for the high affinity dopamine D-2 receptor in bovine striatal membranes

The characterization of [H-3]pramipexole binding to bovine striatal membran es is reported in full experimental detail. According to kinetic experiment s, saturation and competition studies a single binding site can be selectiv ely labeled which turned out to be the high affinity D-2 receptor. Addition of GPP(NH)P resulted in almost complete loss of specific binding. The bovi ne D-2 subtype shows high sequence identity with the human D-2 receptor ind icating that the heterologous competition assays are of interest for the ev aluation of neurotropic drug candidates. Using the representative D-2 agoni sts (I)-7-OH-DPAT, (-)-3-PPP and (S)-7-dipropylaminotetrahydroindolizine th e same rank order of affinities was determined as described for rat striata labeled with [H-3]pramipexole. however, the Ki values turned out to be sig nificantly higher. Furthermore, the system facilitates structure activity r elationship studied on D-2 affinity modulating peptides. Using L-prolyl-L-l eucyl-glycinamide as an example a significant increase of specific radiolig and binding could be measured.