Differential effects of the enantiomers of 3-PPP on dopamine D1-receptors of isolated rabbit retina.

The effects of (+)- and (-)-3-PPP on cAMP levels of rabbit retina were investigated in vitro in the absence or presence of exogenous dopamine. In some experiments, a pre-incubation with reserpine was undertaken to deplete endogenous dopamine before the test. (+)- and (-)-3-PPP were found to be a weak dopamine-agonist and a weak dopamine-antagonist, respectively. Thus, the 3-PPP enantiomers may have opposite actions at the level of postsynaptic dopamine receptors, as previously suggested by studies in vivo.