Bioavailability of pyridoxine in rats fed various levels of casein

Abstract

[ 14C] pyridoxine (PN) was orally administered to male rats and lactating dams fed an 8%, 20%, or 50% casein diet. There was no effect of the level of dietary protein on plasma pyridoxal 5′-phosphate (PLP) concentration. Analysis of fecal radioactivity indicated no dietary effect on the intestinal absorption of [ 14C]PN. There was greater retention of 14C in the liver when male and lactating rats were fed increased amounts of protein. Increased dietary protein resulted in reduced levels of 14C in the brain of the male rats. There was no dietary effect on the urinary excretion of total 14C or [ 14C]4-pyridoxic acid. Increasing the level of dietary protein resulted in increased retention of 14C in the liver of the lactating dams, however, the concentration of 14C and the 14C:protein ratio in milk was not affected. Although not significant, the level of 14C in the liver of the suckling pups was two or three times greater when dams were fed 8% protein than when dams were fed 20% or 50% protein. These results demonstrate that altered tissue distribution of vitamin B-6 occurs with varied protein intake without influencing the metabolic utilization and urinary excretion of vitamin B-6 or plasma PLP concentration, the primary assessment parameter for vitamin B-6 status. Furthermore, increased intake of protein by the lactating rat does not influence the concentration vitamin B-6 or the vitamin B-6:protein ratio in milk.