Adult and suckling (13 days old) rat intestinal brush borders have been purified by
the procedure of Schmitz et al. (25). Enzymatic proteins have been separated by polyacrylamide
gel electrophoresis. In the adult rat, enzyme activities in order from the origin were: maltase/
glucoamylase/sucrase-isomaltase (protein band 3), lactase (protein band 5), maltase/sucraseisomaltase
(protein band 6) and alkaline phosphatase (protein bands 8 and 9). In the suckling rat,
protein band 5 associated with lactase activity was found to be markedly higher compared to the
adult rat. Gels were completely devoid of sucrase-isomaltase activity while protein band 3 was
strikingly reduced and protein band 6 absent. After hydrocortisone administration to suckling rats,
a new band associated with sucrase-isomaltase activity appeared in position 6, whereas protein
band 3 markedly increased with the simultaneous appearance of sucrase-isomaltase activity.
Intralipid was given to adult rats for 4 days either by intragastric or intravenous infusion. The villus height, protein content and the levels of sucrase, lactase and aminopeptidase activities were determined in the jejunum. The results were compared to values found in control rats fed orally with an equilibrated isocaloric diet. Intragastric or intravenous infusion of Intralipid caused (a) a 50% reduction in the protein content of the brush border membrane, (b) a significant drop of the specific (expressed per milligram protein) and segmental (expressed per centimeter intestinal length) activities of the disaccharidases, (c) the maintenance of aminopeptidase activity and (d) the lengthening of the villi in the jejunum. The major loss in disaccharidase activities was obtained when fat was given intravenously. Arguments favoring a hormone-mediated effect of the infused lipids on the intestinal function are presented and discussed.
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