Comparison of [11C]diprenorphine and [11C]carfentanil binding to opiate receptors in humans by positron emission tomography

J. James Frost, Helen S. Mayberg, Bernard Sadzot, Robert F. Dannals, John R. Lever, Hayden T. Ravert, Alan A. Wilson, Henry N. Wagner, Jonathan M. Links

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The kinetics and regional distribution of [11C]carfentanil, a μ-selective opiate receptor agonist, and [11C]diprenorphine, a nonselective opiate receptor antagonist, were compared using paired positron emission tomography studies in two normal volunteers. Kinetics of total radioactivity (counts/mCi/pixel) was greater for [11C]diprenorphine than [11C]carfentanil in all regions. [11C]Carfentanil binding (expressed as the total/ nonspecific ratio) reached near equilibrium at ∼40 min, whereas [11C]diprenorphine showed a linear increase until ∼60 min. Kinetics of specific binding demonstrated significant dissociation of [11C]carfentanil from opiate receptors, whereas little dissociation of [11C]diprenorphine was observed during the 90-min scan session. Regional distributions of [11C]carfentanil and [11C]diprenorphine were qualitatively and quantitatively different: Relative to the thalamus (a region with known predominance of μ-receptors), [11C]diprenorphine displayed greater binding in the striatum and cingulate and frontal cortex compared to [11C]carfentanil, consistent with labeling of additional, non-μ. sites by [11C]diprenorphine. We conclude from these studies that [11C]diprenorphine labels other opiate receptor subtypes in addition to the μ sites selectively labeled by [11C]carfentanil. The nonselective nature of diprenorphine potentially limits its usefulness in defining abnormalities of specific opiate receptor sub-types in various diseases. Development of selective tracers for the δ- and κ-opiate receptor sites, or alternatively use of unlabeled inhibitors to differentially displace μ, δ, and κ subtypes, will help offset these limitations.

Original languageEnglish
Pages (from-to)484-492
Number of pages9
JournalJournal of Cerebral Blood Flow and Metabolism
Issue number4
StatePublished - 1990
Externally publishedYes


  • Carfentanil
  • Diprenorphine
  • Opiate receptors
  • Positron emission tomography


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