No effect of maternal niacin deficiency on niacin metabolism in newborn brain.

The effects of maternal niacin and tryptophan deficiency on: (1) total niacin levels and (2) niacinamide entry into brain, blood, and liver of newborn rabbits were studied. The deficient maternal diet produced a decreased concentration of the oxidized niacinamide-containing vitamers in the liver (73% of controls; P less than 0.05) but not in the brain of newborn rabbits. In both deficient and control newborn rabbits, the entry of [14C]niacinamide into brain and liver was saturable with an increasing [14C]niacinamide concentration in plasma. Also, the formation of [14C]NAD in brain and liver and [14C]niacinamide mononucleotide in blood was saturable. In vitro, the affinity of the saturable accumulation system for [14C]niacinamide in both newborn and adult rabbit brain slices was comparable (0.9 microM). The avid saturable, uptake system for niacinamide in rabbit brain contributes to total niacin homeostasis in brain.