QUANTITATION OF [C-11] DIPRENORPHINE CEREBRAL KINETICS IN MAN ACQUIRED BY PET USING PRESATURATION, PULSE-CHASE AND TRACER-ONLY PROTOCOLS

The quantitation of regional cerebral in vivo opioid receptor rate constants using [C-11]diprenorphine and positron emission tomography (PET) using 3 types of protocol (presaturation, pulse-chase naloxone displacement and tracer-only protocols) together with measurements of regional cerebral blood now is described in normal volunteers. Arterial blood was sampled continuously for radioactivity and was corrected for metabolites and plasma/blood partition of radioactivity to provide a continuous plasma input function. A compartmental model involving 3 tissue compartments was used to describe the regional cerebral pharmacokinetics of the tracer. The compartments comprised: (1) free plus rapidly exchanging non-specifically bound ligand, (2) specifically bound, naloxone displaceable ligand, and (3) a kinetically distinguishable non-specifically bound pool. Regional estimates of fractional rate constants relating to specific binding were obtained using naloxone in a pulse-chase design of tracer displacement. Less precise estimates of these rate constraints were obtained from single-tracer-only studies, but when binding was expressed as the tissue total volume of distribution relative to plasma there was good correlation with regional values obtained from pulse-chase studies performed in the same individuals. The application of these protocols to the measurement of indices of regional-specific opioid receptor binding in the human brain is discussed.