VITAMIN ABSORPTION STUDIES: IV. SITE OF ABSORPTION OF C14-RIBOFLAVIN AND S35-THIAMINE IN THE RAT

Normal adult male rats were killed at time intervals after an oral dose of C14-riboflavin or S35-thiamine. The small intestine (divided into four equal parts), cecum, large intestine, and liver were removed and analyzed for radioactivity. Based upon measurement of radioactivity the vitamins appeared to be absorbed throughout the small intestine. Maximum absorption of riboflavin occurred in the lower ileum and took place 2 to 4 hours after administration of the dose. Thiamine appeared to be absorbed maximally at a higher level in the small intestine and maximum absorption took place within 1 hour of ingestion.Absorption of the radioactive vitamins was estimated by measuring radioactivity in the urine and feces of normal controls and others which had portions of the small intestine removed surgically. Resection appeared to have no effect on the absorption of either vitamin. Cecectomy, however, lowered the availability of both riboflavin and thiamine.