Abstract
Oral glucose supply is important for neonatal calves to stabilize postnatal plasma glucose concentration. The objective of this study was to investigate ontogenic development of small intestinal growth, lactase activity, and glucose transporter in calves (n = 7 per group) that were born either preterm (PT; delivered by section 9 d before term) or at term (T; spontaneous vaginal delivery) or spontaneously born and fed colostrum for 4 days (TC). Tissue samples from duodenum and proximal, mid, and distal jejunum were taken to measure villus size and crypt depth, protein concentration of mucosa and brush border membrane vesicles (BBMV), total DNA and RNA concentration of mucosa, mRNA expression and activity of lactase, and mRNA expression of sodium-dependent glucose co-transporter-1 (SGLT1) and facilitative glucose transporter 2 (GLUT2) in mucosal tissue. Additionally, protein expression of SGLT1 in BBMV and GLUT2 in crude mucosal membranes and immunochemical localization of GLUT2 in the enterocytes were determined. Villus height in distal jejunum was lower in TC than in T. Crypt depth in all segments was largest and the villus height/crypt depth ratio in jejunum was smallest in TC calves. Concentration of RNA was highest in duodenal mucosa of TC calves, but neither lactase mRNA and activity nor SGLT1 and GLUT2 mRNA and protein expression differed among groups. Localization of GLUT2 in the apical membrane was greater, whereas in the basolateral membrane was lower in TC than in T and PT calves. Our study indicates maturation processes after birth for mucosal growth and trafficking of GLUT2 from the basolateral to the apical membrane. Minor differences of mucosal growth, lactase activity, and intestinal glucose transporters were seen between PT and T calves, pointing at the importance of postnatal maturation and feeding for mucosal growth and GLUT2 trafficking.
Highlights
With birth nutrient supply changes from parenteral energy supply by the placenta to oral supply with milk feeding
Glucose transport can be influenced by feeding [16] and it has been assert that the intrinsic activity of glucose transporter 2 (GLUT2) increases with elevated luminal glucose concentration and by trafficking of GLUT2 to the apical membrane [17,18,19], this concept is still under discussion [20]
The ratio of villus height to crypt depth increased along the small intestine in PT and T, but not in TC, and was lowest in jejunum of TC when compared to PT and T
Summary
With birth nutrient supply changes from parenteral energy supply by the placenta to oral supply with milk feeding. Cortisol promotes growth and maturation of organs around birth and increases small intestinal weight as well [4], whereas administration of cortisol to ovine fetus during late gestation affects cell proliferation, but fails to influence enterocyte morphology [5]. Lactose is the main nutritive carbohydrate source in neonatal mammals, which is split into glucose and galactose by the intestinal enzyme lactase. Glucose transport can be influenced by feeding [16] and it has been assert that the intrinsic activity of GLUT2 increases with elevated luminal glucose concentration and by trafficking of GLUT2 to the apical membrane [17,18,19], this concept is still under discussion [20]
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