A study of dopamine receptors in guinea-pig renal tissue

Dopamine and isoprenaline have been examined for their effects on guinea-pig renal blood flow in vivo and on cAMP production in a mainly isolated glomeruli/blood vessel preparation in vitro. The renal vasodilatation caused by both of these drugs can be differentiated by the use of specific antagonists, sulpiride blocking the effects of dopamine, and propranolol the vasodilatation produced by isoprenaline. Similarly, both drugs stimulated cAMP production, isoprenaline being much more active than dopamine (1000X) in this respect. Again, the dopamine antagonist fluphenazine specifically inhibited the dopamine-induced cAMP increases whilst the beta blocker atenolol blocked the rise in cAMP due to isoprenaline but not that due to dopamine. Sulpiride although potently inhibiting dopamine-induced renal vasodilatation was without effect on dopamine-stimulated cAMP levels. This result is similar to that reported in the CNS where sulpiride blocks dopamine activity in a variety of tests but is without effect on the dopamine-stimulated adenylate cyclase. Two dopamine agonists, ADTN and SKF 38393 were tested, and in both preparations had potent dopaminergic activity although SKF 38393 exhibited characteristics of a partial agonist on the adenylate cyclase model.