Effects of insulin, tolbutamide, and glucagon on activities of jejunal carbohydrate-metabolizing enzymes in humans

Gut glucose metabolism in rainbow trout: implications in glucose homeostasis and glucosensing capacity

The main objective of the present study was to evaluate the relative contribution of the intestine to glucose homeostasis in rainbow trout. In a first set of in vivo experiments trout were subjected to oral glucose treatments alone or in combination with insulin injections to assess changes in glucose-related enzymes activities, metabolite levels, and mRNA levels. Rainbow trout gut displays an important glucose metabolism that includes the ability to store glucose as glycogen (mostly in the muscle layers) and a large capacity to oxidize glucose. This constitutes a surprising result for a carnivorous fish. In a second set of in vivo experiments, trout received an oral amino acid solution alone or in combination with insulin injection to determine whether other factors besides fasting could regulate gluconeogenesis in intestine. The results confirm the absence of regulation of gluconeogenesis in trout gut, which does not respond to hormones, glucose, lactate, or amino acid changes, either in vivo or in vitro. We also fully characterized gut glucose metabolism in vitro. We observed that a large amount of glucose is oxidized to lactate, supporting the importance of glucose in gut metabolism. Moreover, we corroborated the minor actions of insulin in trout gut, whereas other hormones such as glucagon-like peptide-1 and C-peptide appear to be major hormonal regulators of glucose metabolism in fish gut. Finally, we obtained the first evidence for the existence of a glucosensing mechanism in the midgut of this carnivorous species.

Brush border and lysosomal marker enzyme profiles in duodenal mucosa from coeliac patients before and after organ culture

Five brush border and 2 lysosomal enzymes were measured in duodenal tissue explants from 21 children and young adults (16 coeliac and 5 non-coeliac) before and after organ culture. Reduced activity of brush border enzymes and increased activity of lysosomal enzymes were recorded in flat mucosas from coeliac patients compared with remission coeliac explants and biopsy specimens from non-coeliac controls. Slightly increased activity of alkaline phosphate and sucrase was recorded during culture (24 h) of coeliac explants. Coeliac specimens in the exacerbation state showed increased activity of acid phosphatase after culture in the presence of gluten, whereas gluten did not provoke detectable alterations in brush border enzyme activities during culture unless the wet weight of material was 1.5 mg or more. In such explants lower activity of brush border enzymes was measured after in vitro gluten exposure than after culture on gluten-free medium. Mucus removed from the specimen surface after culture contained considerable amounts of brush border enzymes and reflected the variations in the tissue homogenates. Culture media contained smaller quantities of enzymes.

Organ culture of adult mouse intestine. III. Behavior of the proteins, DNA content and brush border membrane enzymatic activities

The proteins, the DNA content and the brush border membrane enzyme activities of adult mouse intestinal explants have been measured during a 24-hr organ culture. These activities were not modified in comparison with the controls at the beginning of the culture. The activity of the enzymes secreted in the medium during the 24-hr culture was equal to the activity present in the explants at the start of the culture. These results show that several metabolic functions of the intestine are fully preserved in organ culture.

Organ culture of adult mouse intestine IV. Stimulation of glucose-6-phosphatase in vitro

Explants of adult mouse jejunum have been maintained in organ culture with or without fructose added to the medium in order to stimulate the intestinal glucose-6-phosphatase (G-6-Pase). When the fructose is added, at the beginning of the culture, a three-fold increase of G-6-Pase in measured during the first 24 h. If the fructose is added after 24 h of culture, no significant increase of the G-6-Pase is registered in comparison with the controls. Proteins, DNA content and dissacharidase activities are not modified during the culture. Alkaline phosphatase activity presents a twofold increase in the controls and stimulated explants. The ultrastructural localization of the G-6-Pase is not altered during the culture.