Abstract. We have characterized the modulation of adenylyl cyclase (AC) activity by ligands of dopaminergic receptors in rat striatal homogenate and compared the results with receptorligand binding affinities. Despite the fact that rat striatum contains high level of both dopamine D 1 and D 2 receptors, only the D 1 -specific AC activation by agonists could be determined. All D 1 -receptor agonists (dopamine, dihydrexidine, and A 77636) used were able to increase cAMP accumulation in a concentration-dependent manner, while D 1 -receptor antagonists (SCH23390, SKF83566, and butaclamol) blocked the effects induced by the aforementioned agonists. At the same time, the D 2 -receptor agonist quinpirole and antagonist sulpiride had no effect on cAMP accumulation in striatal homogenate neither on the basal level nor on the activated level of AC, while inhibited [

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New 2-Thioether-Substituted Apomorphines as Potent and Selective Dopamine D 2 Receptor Agonists. -The introduction of substituents at position 2 of the aporphine backbone is suitable for the preparation of 2-O-and 2-S-substituted aporphines with the methanesulfonic acid-mediated rearrangement of thebaine (I). A set of apomorphine derivatives is synthesized with diversely functionalized side chains in the proximity of position 2 of the aporphine skeleton. During the synthesis of mercaptopropionic acid derivative (VIII) the heteroring-fused congener (IX) is formed as well. Two apomorphine congeners, (IVb) and (VI), are identified as D2 full agonists, equipotent to apomorphine, but exhibiting significantly increased D2/D1 selectivity ratios. -(REINART, R.; GYULAI, Z.; BERENYI, S.; ANTUS, S.; VONK, A.; RINKEN, A.; SIPOS*, A.; Eur.