3H-diprenorphine is selective for mu opiate receptors in vivo

The displacement of ³H-diprenorphine from opiate receptors by mu-selective opiates was measured in the mouse striatum and thalamus in vivo. In addition, the regional distribution of opiate receptor binding using ³H-diprenorphine, ³H-naloxone and ³H-lofentanil was measured. The displacement of ³H-diprenorphine by naloxone and carfentanil in vivo showed no differences in the striatum and thalamus suggesting that ³H-diprenorphine binds only to one opiate receptor subtype in vivo. This finding is substantiated by the observation that the mu selective ligands ³H-naloxone and ³H-lofentanil have the same in vivo distribution of receptor binding as ³H-diprenorphine. The implication of these findings for PET imaging of opiate receptor subtypes is discussed.