Effects of dopamine receptor agonists and antagonists at peripheral neuronal and vascular dopamine receptors in the anaesthetised cat.
The potencies of several putative dopamine receptor agonists and antagonists have been determined and compared at neuronal and vascular dopamine receptors in anaesthetised cats. N,N-diethyldopamine and the N,N-di-n-propyl derivatives of 5,6-ADTN (6-amino-5,6,7,8-tetrahydro-1,2-napthalenediol) and 6,7-ADTN (6-amino-5,6,7,8-tetrahydro-2,3-napthalenediol) were, relatively, much more potent agonists than dopamine at neuronal dopamine receptors on the terminals of sympathetic nerves supplying the heart and nictitating membrane than at the vascular dopamine receptors in the mesenteric vascular bed. SK&F 82526 [6-chloro-2,3,4,5-tetrahydro-1-(4-hydroxyphenyl)-1H-3-benzazepine-7,8-di ol] showed the reverse profile. Haloperidol, (+/-) sulpiride, cis alpha-flupenthixol, and fluphenazine were much more potent antagonists at neuronal dopamine receptors than at vascular dopamine receptors. The profiles of activity of the agonists and antagonists show that neuronal and vascular dopamine receptors in the cat are different; in addition, the neuronal dopamine receptors in the cat heart and nictitating membrane closely resemble those in the dog femoral vasculature, whereas the vascular dopamine receptors in the cat mesenteric vascular bed are very similar to those in the dog mesenteric circulation.