Incomplete utilization of pyridoxine-beta-glucoside as vitamin B-6 in the rat

This research was conducted to determine the bioavailability of 5'-O-(beta-D-glucopyranosyl) pyridoxine (PN-glucoside) during chronic administration in a depletion-repletion bioassay. PN-glucoside was found previously to constitute a major portion of the total vitamin B-6 in many foods of plant origin. Following a 14-d depletion period, rats were fed diets containing graded levels of either free pyridoxine (PN) or PN-glucoside for 17 d. Slope ratio analysis of dose-response curves, on the basis of growth and plasma pyridoxal 5-phosphate (PLP) concentration, indicated 10-34% utilization of PN-glucoside relative to the molar response to PN. Erythrocyte aspartate amino-transferase (AspAT) activity and urinary 4-pyridoxic acid concentration were lower and the stimulation of AspAT activity by exogenous PLP was greater for rats fed PN-glucoside than for those fed PN, which indicated reduced vitamin B-6 nutriture in response to PN-glucoside. A constant 7-9% of the ingested PN-glucoside was detected in urine in intact form at all dosage levels. These results provide further evidence of incomplete bioavailability of PN-glucoside and indicate that its extent of utilization is not influenced by its level of dietary intake.