Effect of 3‐PPP, a putative dopamine autoreceptor agonist, on [3H]ligand binding to dopamine receptors of calf and rat striatum

Abstract

Abstract3‐(3‐Hydroxyphenyl)‐N‐n‐propyliperidine (3‐PPP) is most effective in inhibiting [3H]apomorphine binding in rat striatal membranes, with Ki values of 63 nM. 3‐PPP was six to 27 times less effective when it competed with the binding of [3H]dopamine or [3H]spiperone in calf and rat striatal membranes. At concentrations up to 10 μM, 3‐PPP failed to substitute for dopamine in the activation of adenylate cyclase in rat striatal membranes. 3‐PPP at 4.8‐5 μM caused 50% inhibition of catecholamine uptake in synaptosomes of corpus striatum and hypothalamus, therefore appearing to be a relatively weak uptake inhibitor. The higher affinity of 3‐PPP for [3H]apomorphine binding sites is consistent with its binding to a subset of dopamine receptors which are characterized by a high affinity for both the agonist and antagonist of dopamine.