[Effective intraluminal concentration of riboflavin and pyridoxine in various intestinal segments of the rat].

The study was designed to determine the intraluminal concentration of riboflavin and pyridoxine in different gastrointestinal segments of rats as a function of time after intragastric application of the vitamins. A semi-liquid diet with 14C-riboflavin and 3H-pyridoxine was delivered by tube. After a period of 30 minutes, 1, 2, 6, 12 or 24 hours, respectively, concentrations of the vitamins were determined by radio-chemical methods in stomach, duodenum, jejunum and ileum. In the duodenum highest concentration of riboflavin (10.4 nmol/l) was reached 2 hours, that of pyridoxine (5.5 nmol/l) 1.5 hours after intubation. In jejunum maximum concentration of both vitamins--4.1 nmol/l riboflavin and 3.0 nmol/l pyridoxine--was found 1.5 hours after tube feeding. As discussed for riboflavin, precise information about the physiologically relevant intraluminal concentration of micro-nutrients in the absorbing intestinal segments is essential, especially if transport mechanisms have to be elucidated.