抄録
The metabolism of NAD was investigated with mice following the administration of NAD- (nicotinamide-7^<14>C) and NAD-(adenosine-U^<l4>C). When NAD was given intravenously, it was not utilized directly as a coenzyme, and was degraded immediately to nicotinamide and presumably to adenosine diphosphate ribose. The ADP-ribose moiety was converted rapidly to ADP, AMP, ATP and two unknown metabolites. Even 20 seconds after the injection of NAD-(nicotinamide-7^<14>C) , more than 90% of radioactivity in the blood was shown to be nicotinamide. The nicotinamide disappeared rapidly from the blood and was incorporated into various tissues and organs. In addition, a portion of nicotinamide was excreted into the gastrointestinal tract. The radioactive material was reabsorbed and reutilized as a precursor to NAD in various tissues. When NAD-(nicotinamide-7^<14>C) was given orally, it was shown to be degraded to nicotinamide. The latter compound was absorbed efficiently and distributed in every tissue and organ. Practically no radioactivity was found in the feces. About 20% of total radioactivity was expired as ^<14>C0_2 Whithin 8 hours. Probably, the intestinal bacteria were responsible for this complete degradation of the nicotinamide.
