11C-methionine uptake to the pancreas and its secretion: a positron emission tomography study in humans

The aim of this study was to investigate the uptake of [11C-methyl]-L-methionine (11C-methionine) in the human pancreas by analyzing dynamic positron emission tomography (PET) images and the duodenal aspirate. A double-lumen tube was inserted in the duodenum and dynamic PET was performed in seven healthy volunteers for 110 min after intravenous (i.v.) injection of 11C-methionine during the continuous i.v. administration of secretin (125 ng/kg/h) and cerulein (30 ng/kg/h). For the calculation of the radioactivity in the pancreas, the regions of interest were set on the PET images. Radioactivity was measured in 10-min fractions of duodenal juice. After i.v. injection, 11C-methionine accumulated in the pancreas within a few minutes, and the radioactivity plateaued during the study. The radiolabeled proteins in the duodenal juice increased linearly 30 min after 11C-methionine injection, but the relative rates of radioactivity in the protein precipitate to the total count in the duodenal juice were 44-48%. From these findings, it was concluded that 11C-methionine accumulation in the pancreas is very rapid after the i.v. administration, and only a part of methionine uptake to the pancreas is incorporated into secretory proteins. The pancreatic 11C-methionine uptake detected by PET may represent a new aspect of exocrine pancreatic function that has not been expressed by the conventional intubation method.