COMPARISON OF [C-11] DIPRENORPHINE AND [C-11] CARFENTANIL IN-VIVO BINDING TO OPIATE RECEPTORS IN MAN USING A DUAL DETECTOR SYSTEM

A simple dual detector coincidence system was used to measure the binding of [C-11]carfentanil and [C-11]diprenorphine to opiate receptors in normal volunteers before and after the administration of naloxone. Total radioactivity without naloxone and the ratio of total/non-specific radioactivity was 2 times greater for [C-11]diprenorphine than [C-11]carfentanil. The dose of naloxone required to maximally block specific [C-11]diprenorphine binding was 10 times that for [C-11]carfentanil, indicating that [C-11]diprenorphine labels opiate receptor subtypes in addition to mu opiate receptors.