| Abstrakt: |
By using selective dopamine (DA) receptor agonists and antagonists, we have demonstrated previously the presence of DA-2- and DA-1-like DA receptors in the stellate ganglia of the dog. Activation of either DA-2- or DA-1-like receptors by quinpirole or fenoldopam, respectively, leads to inhibition of ganglionic transmission. In the present study we have examined the involvement of DA receptor subtypes in the action of DA on ganglionic transmission. Inasmuch as stimulation of DA receptors is linked to the activation (DA-1) or inhibition (DA-2) of the enzyme adenylate cyclase, we have also measured the accumulation of cyclic AMP (cAMP) for biochemical characterization of ganglionic DA receptors. In isolated stellate ganglia treated with phentolamine and propranolol, DA caused concentration-dependent inhibition of ganglionic transmission as evidenced by reductions in the amplitude of the evoked postganglionic compound action potentials. The inhibitory effect of DA on ganglionic transmission was antagonized by both the DA-1 receptor antagonist, R-sulpiride, and the DA-2 receptor antagonist, S-sulpiride. However, the more potent and selective DA-1 receptor antagonist, SCH-23390, failed to antagonize the DA-induced inhibition of ganglionic transmission. Isolated stellate ganglia were also utilized for the measurement of cAMP. Neither DA nor the selective DA-1 receptor agonist, fenoldopam, caused any significant changes in cAMP, suggesting the lack of an adenylate cyclase-linked DA-1 receptor in the ganglia. On the other hand, beta adrenoceptor activation by isoproterenol produced a 3-fold increase in cAMP content of the stellate ganglia.(ABSTRACT TRUNCATED AT 250 WORDS) |
