KINETIC CONSTANTS OF ALPHA-METHYL-D-GLUCOSIDE TRANSPORT IN THE CHICK SMALL-INTESTINE DURING PERINATAL-DEVELOPMENT

The kinetic parameters of alpha-methyl-D-glucoside (alpha GlclMe) have been determined in the small intestine in order to establish developm ental and regional changes in the apical transport in embryos and newl y hatched chicks. Results show that the apparent Michaelis constant (K -m) values did not change during the period studied in each region of the small intestine. However, the ileum showed a smaller K-m than that of the duodenum and jejunum, indicating an increase of the affinity o f the carrier in the distal portion of the intestine and a significant contribution of the ileum to overall sugar absorption in the perinata l period. There were important changes in the diffusional component an d in the mediated transport system capacity during this period, as wel l as in the different regions of the intestine. Significant increases in the maximal rate of transport (V-max) were observed in all regions during the embryonic period until the second day after hatching, follo wed by a decline during the first week. During all the period studied, V-max values from the jejunum were significantly greater than those f rom both the duodenum and the ileum at every age studied showing that the jejunum is the segment that is best suited for Na+-mediated uptake . Such changes which occur when the need for nutrients for rapid devel opment are at their highest are not solely a result of diet compositio n, but rather in accordance with a genetic programme. Copyright (C) 19 96 Elsevier Science Ireland Ltd.