Comparison of Peptidic and Nonpeptidic δ-Opioid Agonists on Guanosine 5′-O-(3-[35S]thio)triphosphate ([35S]GTPγS) Binding in Brain Slices from Sprague-Dawley Rats
- Emily M. Jutkiewicz,
- Nicholas P. Walker,
- John E. Folk,
- Kenner C. Rice,
- Philip S. Portoghese,
- James H. Woods and
- John R. Traynor
- Department of Pharmacology, University of Michigan Medical School, Ann Arbor, Michigan (E.M.J., N.P.W., J.H.W., J.R.T.); Laboratory of Medicinal Chemistry, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland (J.E.F., K.C.R.); and Department of Medicinal Chemistry, College of Pharmacy, University of Minnesota, Minneapolis, Minnesota (P.S.P.)
- Address correspondence to:
Dr. John R. Traynor, 1301 Medical Science Research Building 3, Department of Pharmacology, University of Michigan Medical School, Ann Arbor, MI 48109-0632. E-mail: jtraynor{at}umich.edu
Abstract
Previous studies have demonstrated that peptidic and nonpeptidic δ-opioid receptor agonists have different effects depending on the measure. For example, nonpeptidic δ-opioid agonists, but not peptidic agonists, produce convulsions in rats, and in vitro studies suggested that peptidic and nonpeptidic δ-opioid agonists might have differential mechanisms of receptor downregulation. The present study evaluated potential differences between peptidic and nonpeptidic δ-opioid agonists in their ability to activate G proteins using guanosine 5′-O-(3-[35S]thio)triphosphate ([35S]GTPγS) autoradiography experiments in rat brain slices. The peptidic agonist [d-Pen2,d-Pen5]-enkephalin and the nonpeptidic agonist (+)BW373U86 [(+)-4-[α(R)-α-[(2S,5R)-2,5-dimethyl-4-(2-propenyl)-1-piperazinyl]-(3-hydroxyphenyl)methyl]-N,N-diethylbenzamide] demonstrated concentration-dependent increases in [35S]GTPγS binding that were attenuated by the δ-opioid antagonist naltrindole. (+)BW373U86 was more potent and efficacious than the peptidic agonist, and this difference remained consistent across brain regions where significant stimulation was observed. In addition, multiple δ-opioid compounds were evaluated for their agonist activity in this assay. These data suggested that differences between peptidic and nonpeptidic δ-opioid agonists in behavioral studies were most likely caused by differences in agonist efficacy. Finally, these data also revealed that [35S]GTPγS autoradiography could be used to compare efficacy differences among agonists across various brain regions in rat brain slices.
Footnotes
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This work was supported by U.S. Public Health Service Grants DA00254, T32 GM07767, and T32 DA07267.
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doi:10.1124/jpet.104.078741.
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ABBREVIATIONS: [35S]GTPγS, 5′-O-(3-[35S]thio)triphosphate; DPDPE, [d-Pen2,d-Pen5]-enkephalin; SNC80, (+)-4-[α(R)-α-[(2S,5R)-2,5-dimethyl-4-(2-propenyl)-1-piperazinyl]-(3-methoxyphenyl)methyl]-N,N-diethylbenzamide; OMI, oxymorphindole; SIOM, spiroindanyloxymorphone; (+)BW373U86, (+)-4-[α(R)-α-[(2S,5R)-2,5-dimethyl-4-(2-propenyl)-1-piperazinyl]-(3-hydroxyphenyl)methyl]-N,N-diethylbenzamide; NSB, nonspecific binding; NTI, naltrindole; TAN67, 2-methyl-4aa-(3-hydroxyphenyl)-1,2,3,4,4a,5,12,12aα-octahydroquinolino[2,3,3-g]isoquinoline dihydrobromide (SB205607); FrCtx, frontal cortex; PCtx, prelimbic cortex; CCtx, cingulate cortex; NAcc nucleus accumbens; CP, caudate putamen; HPC, hippocampus; Amyg, amygdala; PirCtx, piriform cortex; Thal, thalamus; Hypothal, hypothalamus; SN, substantia nigra; PAG, periaqueductal gray; PN, pontine nuclei.
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- Received October 1, 2004.
- Accepted November 30, 2004.
- The American Society for Pharmacology and Experimental Therapeutics
