Organ distribution and metabolism of [13N]nicotinamide in mice.

The organ distribution and the metabolic fate of 13N[amide-13N]nicotinamide ([13N]NAM) were studied in order to evaluate its potential as a radiotracer. After administration, [13N]NAM is transported, mainly by simple diffusion, into the brain and heart, where part of the tracer is metabolized into hydrophilic compounds ([13N]NAD etc.) and trapped. A very high radioactivity is accumulated in the small intestine, probably due to bile duct excretion of the tracer and its metabolites. [13N]NAM was found to be a useful tracer for the study of the utilization of the vitamin, nicotinamide.