Methionine accumulation in villi isolated from maturing rat intestine

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Abstract
1. This study compares the absorption rates of methionine in 15-day-old rats (preweaned) and 30-day-old rats (post-weaned), and the effect of varying initial substrate concentration on the absorption rate of methionine in tissue removed from specific sites in the small intestine. 2. The experiments utilize a new in vitro method, the villus technique, permitting evaluation of the mucosal (villus) absorptive cells separated from the relatively non-transporting muscle and connective tissue components (non-villus tissue). 3. When the villus technique was used in a comparative age study of absorption by jejunal and duodenal tissue, it was found that at initial methionine concentrations below 1·0 m M, no difference in the transport rate between preweaned and post-weaned animals was observed. 4. However, in preweaned animals, methionine transport is faster in the ileum than in the jejunum or duodenum. 5. With initial methionine concentration greater than 1·0 m M, duodenal and jejunal villi from preweaned animals transport methionine better than villi from older animals. 6. At these higher methionine concentrations there is a slightly better transport by ileal villi from 30-day-old rats than in the younger group. 7. With increasing initial concentration of methionine, physiological changes are shown to occur during maturation because transport rates into villi of mature duodenal and jejunal tissues are slower than into similar tissue from preweaned rats. 8. The underlying physiological changes responsible for the transport rate differences are not known. 9. The results reported indicate that following maturation, the absorbing mucosal cells from the duodenum, jejunum and ileum have an equal capacity for methionine accumulation. 10. The apparent localization of the major amino acid transport to the ileum as reported by others may be an artifact reflecting the inclusion of an undetermined amount of non-absorbing muscle mass in the calculation of intestinal transport.