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  • Title: Mu- and delta-opioid receptors inhibitorily linked to dopamine-sensitive adenylate cyclase in rat striatum display a selectivity profile toward endogenous opioid peptides different from that of presynaptic mu, delta and kappa receptors.
    Author: Schoffelmeer AN, De Vries TJ, Hogenboom F, Mulder AH.
    Journal: J Pharmacol Exp Ther; 1993 Oct; 267(1):205-10. PubMed ID: 8229747.
    Abstract:
    The apparent affinities of endogenous opioid peptides for noncompetitively interacting mu and delta receptors, inhibitorily linked to dopamine (DA) D-1 receptor-stimulated adenylate cyclase, were investigated in superfused rat striatal slices exposed to 40 microM DA in the presence of 10 microM of the selective D-2 receptor antagonist (-)sulpiride. In the presence of peptidase inhibitors, a comparison was made with the apparent affinities of opioid peptides toward independent presynaptic opioid receptors in brain slices. beta-Endorphin had an about 100-fold higher apparent affinity (EC50: 1 nM) toward presynaptic mu-opioid receptors, mediating inhibition of the electrically evoked neocortical [3H]norepinephrine release, than for the striatal adenylate cyclase-coupled mu receptors. In contrast, the kappa-opioid receptor agonist dynorphin A1-13 displayed a similar apparent affinity (EC50: 0.1 microM) toward these functionally different mu receptors. Both Leu- and Met-enkephalin showed only a 3-fold higher apparent affinity (EC50: 30 nM) for presynaptic delta-opioid receptors, mediating inhibition of striatal [14C]acetylcholine release, than for presynaptic mu receptors. However, whereas Leu-enkephalin had a similar apparent affinity for presynaptic and adenylate cyclase-coupled delta receptors, Met-enkephalin displayed a 30-fold selectivity toward the latter receptors. Studying the inhibitory effect of Met-enkephalin on striatal adenylate cyclase stimulated by endogenously released (amphetamine-induced) DA, its very high affinity appeared to be inversely related to the activation of inhibitory DA D-2 receptors.(ABSTRACT TRUNCATED AT 250 WORDS)
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