Accumulation of radioactivity in the pancreas after intravenous administration of [13N]ammonia.

A biodistribution study of [13N]ammonia in rats showed a high accumulation of radioactivity in the pancreas soon after the intravenous injection of this tracer. In humans, the pancreas was also clearly visualized by dynamic positron emission tomography soon after the intravenous injection of [13N]ammonia. To investigate the mechanism of the pancreatic accumulation of [13N]ammonia, in vitro studies with pancreatic slices and in vivo biodistribution and metabolism studies were carried out in rats. The results indicated that [13N]ammonia enters the pancreas from the blood by diffusion at a rate dependent on local blood flow, and then is rapidly incorporated into the amino acid fraction (mainly the glutamine fraction), followed by its incorporation into protein. These findings suggest that [13N]ammonia could be useful for diagnostic imaging of the pancreas.