Abstract
[Dmt1]DALDA (H-Dmt-d-Arg-Phe-Lys-NH2; Dmt = 2′,6′-dimethyltyrosine) is a dermorphin analog that shows high affinity and selectivity for the μ opioid receptor. The intrathecal potency of [Dmt1]DALDA far exceeded its affinity at μ receptors and suggests that other mechanisms must be involved in its action in the spinal cord. The affinity and selectivity of [Dmt1]DALDA was determined using cell membranes expressing cloned human μ, δ, and κ opioid receptors. Competitive displacement binding with [3H][Dmt1]DALDA, [3H]DPDPE (H-Tyr-d-Pen-Gly-Phe-d-Pen), and [3H]U69,593 [(5α,7α,8β)-(+)-N-methyl-N-(7-[1-pyrrolidinyl]-1-oxaspiro[4.5]dec-8-yl)-benzeneacetamide] revealed Ki of 156 ± 26 pM for μ opioid receptor (MOR), 1.67 ± 0.04 μM for δ opioid receptor (DOR), and Ki of 4.4 ± 1.7 nM for κ opioid receptor (KOR), respectively. [Dmt1]DALDA increased guanosine 5′-O-(3-[35S]thiotriphosphate) binding in MOR, DOR, and KOR membranes, with EC50 being 17 (8.8–33) nM, 2 (1.2–3.2) μM, and 124 (15–1000) nM, respectively. Intrathecal [Dmt1]DALDA inhibited the tail-flick response in mice with ED50 = 1.22 (0.59–2.34) pmol. Intrathecal administration of an antiserum against dynorphin A(1-17) or [Met5]enkephalin significantly attenuated the response to i.t. [Dmt1]DALDA, resulting in ED50 of 6.2 (3.6–12.6) pmol and 6.6 (3.5–19.6) pmol, respectively. Neither antisera had any effect on the response to i.t. morphine. Intracerebroventricular (i.c.v.) [Dmt1]DALDA was not affected by previous i.c.v. administration of anti-Dyn or anti-ME. Pretreatment with norbinaltorphimine or naltriben also attenuated the antinociceptive response to i.t., but not i.c.v., [Dmt1]DALDA. These data suggest that i.t. [Dmt1]DALDA causes the release of dynorphin and [Met5]enkephalin-like substances that act at κ and δ receptors, respectively, to contribute to the extraordinary potency of [Dmt1]DALDA.
Footnotes
-
This work was supported, in part, by the National Institute on Drug Abuse (PO1 DA08924 and R37-DA02475).
-
DOI: 10.1124/jpet.102.048561
- Abbreviations:
- [Dmt1]DALDA
- H-Dmt-d-Arg-Phe-Lys-NH2
- Dmt = 2′,6′-dimethyltyrosine
- [35S]GTPγS, guanosine 5′-O-(3-[35S]thiotriphosphate)
- hMOR
- cloned human μ opioid receptor
- hDOR
- cloned human δ opioid receptor
- hKOR
- cloned human κ opioid receptor
- DAMGO
- H-Tyr-d-Ala-Gly-NMePhe-Gly-ol
- DPDPE
- H-Tyr-d-Pen-Gly-Phe-d-Pen
- DSLET
- [d-Ser2,Leu5]-enkephalin-Thr
- U69,593
- (5α,7α,8β)-(+)-N-methyl-N-(7-[1-pyrrolidinyl]-1-oxaspiro[4.5]dec-8-yl)-benzeneacetamide
- Received December 24, 2002.
- Accepted January 23, 2003.
- The American Society for Pharmacology and Experimental Therapeutics
JPET articles become freely available 12 months after publication, and remain freely available for 5 years.Non-open access articles that fall outside this five year window are available only to institutional subscribers and current ASPET members, or through the article purchase feature at the bottom of the page.
|