The Effect of Excessive Nicotinamide Feeding on Rabbits and Guinea Pigs

Slightly depressed growth and fatty livers were observed in animals fed moderate amounts of nicotinamide, while larger quantities completely inhibited growth (1,2). The fatty livers were found to be susceptible to the action of choline, while only methionine was found to alleviate the growth inhibition. These phenomena were ascribed to the forced synthesis of trigonelline from nicotinamide with consequent diminution of the “labile methyl” supply, or, more specifically, the supply of methionine. It has since been demonstrated (3) that the methylated excretory product resulting from nicotinamide feeding is not trigonelline but N1-methylnicotinamide (F,). However, it was not determined whether the effects of nicotinamide feeding were due solely to the diminution in the “labile methyl” supply or to toxicity of the excess, unmethylated nicotinamide. In the present work it has been found that the ingestion of large quantities of nicotinamide by young rabbits and guinea pigs does not impair their growth. Since neither of these species excreted extra Nl-methylnicotinamide after nicotinamide feeding, it is concluded that the toxic effects of nicotinamide in the rat are due entirely to the synthesis of Nl-methylnicotinamide and consequent depletion of available methionine.