DOPAMINE D-1 RECEPTOR AGONISTS DISPLAY A DIFFERENT INTRINSIC ACTIVITY IN RAT, MONKEY AND HUMAN ASTROCYTES

Measuring dopamine D-1 receptor stimulated cyclic AMP production in cultured astrocytes from rat, monkey and human brain, we demonstrate that the 'classical' drug SKF 38393 (7,8-dihydroxy-1-phenyl-2,3,4,5-tetrahydro-1 H-3-benzazepine) is a partial agonist with particularly low intrinsic activity in primates. Furthermore, its analogue SKF 81297 (6-chloro-7,8-dihydroxy-1-phenyl-2,3,4,5-tetrahydro-1 H-3-benzazepine) is shown to be a full agonist in rats but a partial, albeit more efficacious, agonist in primates, whereas the benzopyran A 68930 ((1R,3S)-1-aminomethyl-5,6-dihydroxy-3-phenyl-isochroman HCl) displays full efficacy in both species. The data suggest that cultured astrocytes provide a good model to study species differences in the pharmacological characteristics of dopamine D-1 receptor agonists and indicate that SKF 38393 is not suited to study dopamine D-1 receptor function in primates.