Dopamine D1 and D2 receptor selectivities of phenyl-benzazepines in rhesus monkey striata

Several phenyl-benzazepine compounds, putatively selective dopamine D1 receptor agonists, have been used to study the effects of dopamine D1 receptor stimulation in rodents and nonhuman primates. However, the dopamine receptor selectivities of these compounds have not been established in nonhuman primates. Accordingly, the relative selectivities of six phenyl-benzazepines for dopamine D1-like and D2-like receptors were assessed in rhesus monkey and, for comparison, rat striata. The compounds tested had higher affinity for D1 than D2 receptors in both species; however, their selectivity varied by up to three orders of magnitude. GTP (100 microM) reduced agonist binding at the high-affinity state of the dopamine D1 receptor, but the magnitude of the effect of GTP did not reliably predict a compound's efficacy. Furthermore, a history of cocaine self-administration did not appear to influence dopamine receptor binding characteristics in the rhesus monkeys in this study. The present results will aid the comparison of dopamine receptor binding characteristics and behavioral effects of D1 dopamine receptor agonists.