Effects of YM 435 and A 77636 on dopamine D-1 receptors in bovine retina in vitro.

1. Homogenates of bovine retinas were used to study the capacities of two new dopamine (DA) receptor agonists, e.g. YM 435 and A 77636, to interact with D1 receptors. 2. Adenylate cyclase experiments. YM 435 and A 77636 enhanced cAMP accumulation, with EC50 values of 1.97 microM and 22.9 nM, respectively. The receptor-mediated nature of the effects of these two novel D1 agonists was shown by the abilities of both SCH 23390 or (+)-butaclamol to inhibit the agonist-induced increase of cAMP formation. 3. Binding experiments. The same agonists were also tested for competition with 3H-SCH 23390 for binding to D1 receptors. IC50 values for YM 435 and A 77636 were 8.15 microM and 6.15 nM, respectively. 4. The results of the present report demonstrate the suitability of bovine retina in vitro to evaluate the specificity of new DA D1 agonists at the receptor level.