Abstract
The constrained opioid peptide (2S,3R)β-methyl-2′,6′-dimethyltyrosine-l-tetrahydroisoquinoline-3-carboxylic acid [(2S,3R)TMT-l-Tic-OH] exhibits high affinity and selectivity for the δ-opioid receptors (Liao et al., 1997). In the present study, we examined the pharmacological properties of (2S,3R)TMT-l-Tic-OH in mouse brain. A 5′-O-(3-[35S]thiotriphosphate) ([35S]GTPγS) binding assay was used to determine the effect of (2S,3R)TMT-l-Tic-OH on G protein activity in vitro, in mouse brain membranes. δ- (SNC80; (+)-4-[(αR)-α-((2S,5R)-4-allyl-2,5-dimethyl-1-piperazinyl)-3-methoxy-benzyl]-N,N-diethyl-benzamide) or μ- (DAMGO; [d-Ala2, Me-Phe4,Gly(ol)5]enkephalin) selective opioid full agonists stimulated [35S]GTPγS binding in mouse brain membranes 150 ± 4.5% and 152 ± 5.7% over the basal level, respectively. (2S,3R)TMT-l-Tic-OH did not influence basal [35S]GTPγS binding in mouse brain membranes but dose dependently shifted the dose-response curve of SNC80 to the right, with a Ke value of 3.6 ± 0.7 nM. In contrast, (2S,3R)TMT-l-Tic-OH had no effect on the dose-response curve of the μ-selective opioid agonist, DAMGO. Warm water (55°C) tail-flick and radiant heat paw-withdrawal tests were used to determine the in vivo nociceptive properties of (2S,3R)TMT-l-Tic-OH in the mouse. Intracerebroventricular injection of (2S,3R)TMT-l-Tic-OH had no significant effect on withdrawal latencies in either nociceptive tests. (2S,3R)TMT-l-Tic-OH (30 nmol/mouse) attenuated deltorphin II- but not DAMGO-mediated antinociception (40 ± 13 and 100% of maximal possible effect, respectively) when administered intracerebroventricularly 10 min before the agonist. Taken together these results suggest that (2S,3R)TMT-l-Tic-OH is a potent highly selective neutral δ-opioid antagonist in mouse brain.
Footnotes
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This work was supported in part by grants from the U.S. Public Health Service and from the National Institute of Drug Abuse (DA06284 and DA13449).
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DOI: 10.1124/jpet.102.042929
- Abbreviations:
- (2S,3R)TMT-l-Tic-OH
- (2S,3R)β-methyl-2′,6′-dimethyltyrosine-l-tetrahydroisoquinoline-3-carboxylic acid
- hDOR
- human δ-opioid receptor
- CHO
- Chinese hamster ovary
- [35S]GTPγS
- guanosine-5′-O-(3-[-[35S]thio)triphosphate
- SNC80
- (+)-4-[(αR)-α-((2S,5R)-4-allyl-2,5-dimethyl-1-piperazinyl)-3-methoxy-benzyl]-N,N-diethylbenzamide
- DAMGO
- [d-Ala2,Me-Phe4,Gly(ol)5]enkephalin
- Ke
- dissociation constant from Schild analysis
- MPE
- maximal possible effect
- DPDPE
- [d-Pen2,d-Pen5]-enkephalin
- ICI 174,864
- N,N-diallyl-Tyr-Aib-Aib-Phe-Leu-OH
- SR 141,716
- N-(piperidin-1-yl)-5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboximide hydrochloride
- Received August 13, 2002.
- Accepted October 8, 2002.
- The American Society for Pharmacology and Experimental Therapeutics
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