Glucose metabolism in the rat small intestine: the effect of glucose analogues on hexokinase activity.
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ABSTRACT:
SUBMITTER: Jones GM
PROVIDER: S-EPMC1177568 | biostudies-other | 1973 Jan
REPOSITORIES: biostudies-other
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Project description:1. The effect of three dietary components on hexokinase activity in the mucosa of rat small intestine was studied in vivo. Glucose, amino acids or an emulsion of monoglyceride with long-chain fatty acids were given by stomach tube to previously starved rats, and hexokinase activity was determined in the particle-free supernatant of mucosal homogenates. The formation of lactate from glucose and glucose 6-phosphate respectively was also measured. 2. When the three dietary components were given in isocaloric amounts, only glucose brought about an increase in hexokinase activity. 3. Intravenous injection of a similar amount of glucose to that given orally did not alter hexokinase activity. 4. An increase in the hexokinase activity of the particle-free supernatant prepared from mucosal homogenates was also observed after sacs of the small intestine of starved rats had been incubated in vitro in a medium containing glucose. Hexokinase activity increased to the values observed in corresponding preparations from fed rats, and this increase was strictly glucose-dependent.
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Project description:1. The effect of perfusion on the activities of hexokinase and lactate dehydrogenase was studied in the proximal half of the small intestine of fed and starved rats. 2. Perfusion of preparations from starved rats with a medium containing glucose caused a significant increase in hexokinase activity of the particle-free supernatant. The increase in activity was observed as early as 5min after the start of perfusion and persisted for up to 66min of perfusion. No increase in hexokinase activity of the particle-free supernatant was observed when a medium containing mannitol was used. As a further control, preparations from fed rats were perfused under the same conditions. With the medium containing glucose, the hexokinase activity of the particle-free supernatant remained unchanged during the first 15min of perfusion and thereafter fell gradually until, after 66min of perfusion, 73% of the original activity was retained. 3. The activity of lactate dehydrogenase in the particle-free supernatant prepared from the proximal half of the untreated small intestine of starved rats was significantly lower than in corresponding preparations from fed animals. However, it did not change significantly on perfusion with media containing either mannitol or glucose. 4. The distribution of hexokinase activity between total particulate fraction and particle-free supernatant was measured in preparations from starved rats after perfusion for 5-10min. In preparations that had not been perfused the ratio of hexokinase activity in total particulate fraction/particle-free supernatant was significantly higher in starved than in fed animals. After perfusion with a medium containing glucose, the total homogenate activity had not changed significantly, whereas the ratio of hexokinase activity in total particulate fraction/particle-free supernatant decreased significantly and approached the value obtained with fed animals. 5. The results agree with the view that the glucose-dependent increase of hexokinase activity in the soluble cell compartment as observed in vivo and in vitro in the intestinal mucosa of starved rats is brought about by a release of hexokinase activity from a particulate subcellular structure(s).
| S-EPMC1185321 | biostudies-other
Project description:1. The intracellular distribution of hexokinase activity was studied in the mucosa of rat and guinea-pig small intestine. In the rat 60% and in the guinea pig 45% of the hexokinase activity of homogenates were recovered in a total particulate fraction that contained only 5-17% of the homogenate activity of hexose phosphate isomerase, pyruvate kinase, lactate dehydrogenase and overall glycolysis (formation of lactate from glucose). 2. Fractionation of homogenates from guineapig small intestine showed that the particulate hexokinase activity was chiefly in the mitochondrial fraction with a small proportion in the nuclei plus brush-border fraction. 3. After chromatography of the particle-free supernatants on DEAE-cellulose, hexokinase types I and II were determined quantitatively. No evidence was obtained for the presence of hexokinase type III or glucokinase. In the preparations from guinea pigs, hexokinase types I and II amounted to 69% and 31% respectively of the eluted activity; the corresponding values for preparations from rats were 5.8% and 94.2%. 4. Total and specific hexokinase activities decreased significantly in homogenates and particle-free supernatants prepared from the intestinal mucosa of rats starved for 36hr. and increased again after re-feeding. The decrease in hexokinase activity in the particle-free supernatant from starved rats was chiefly due to a decrease in the type II enzyme.
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Project description:Glucose transport and metabolism by rat small intestine was investigated by using a preparation for the combined perfusion of the lumen and the vascular bed. 2. When 5 mM-glucose was present in the lumen, only 29% was transported unchanged to the vascular side. Lactate output into the vascular and luminal fluids accounted for a further 53% and 4% respectively of the glucose taken up from the lumen. 3. Glucose was readily taken up when added at 5 mM to the vascular compartment only. Vascular lactate output accounted for approx. 33% of the glucose uptake, and luminal lactate for 6%. 4. When 2 mM-glucose was added to the lumen with 5 mM-glucose in the vascular perfusate, there was no detectable net transport of glucose to the vascular side. However, of the glucose taken up from the lumen, 31% and 2% could be accounted for by increases in vascular and luminal lactate respectively. 5. When 10 mM-glucose was added to the lumen, with 5 mM-glucose in the vascular perfusate, 33% of the glucose disappearing from the lumen was transported to the vascular side. Extra lactate output to the vascular and lumen perfusates accounted for 50% and 9% respectively of the glucose uptake from the lumen. 6. These studies indicate that at low luminal glucose concentrations no sugar is transferred to the blood unchanged, and at sugar concentrations of 5--10 mM only 25--50% of the glucose leaving the lumen reaches the serosal side intact. Furthermore, the small intestine has a greater propensity to form lactate from luminal glucose than from vascular glucose.
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Project description:In common with other phosphofructokinase isoenzymes, phosphofructokinase in the epithelial cells of rat small-intestinal mucosa is activated by fructose 2,6-bisphosphate. However, fructose 2,6-bisphosphate was found not to be present in mucosa as judged by three criteria: (1) chromatography on Sephadex G-25 of crude mucosal extracts from fed rats did not result in a decrease, or indeed any change, in the activity of phosphofructokinase under suboptimal conditions at pH7; (2) ultrafiltrates of mucosal extracts did not possess any acid-labile activating activity when tested against chromatographed liver phosphofructokinase; (3) phosphofructokinase-2 activity was not detectable in mucosal extracts. Furthermore, the perfusion in vitro of isolated loops of jejunum or the incubation of mucosal scrapings from either fed rats or rats starved for 48 h showed that the activity of mucosal phosphofructokinase is not subject to short-term regulation by glucose. These observations are consistent with the view that phosphofructokinase is the rate-limiting enzyme of glycolysis in intestinal mucosa and account for the fact that the rate of glucose utilization by rat small intestine is not very responsive to changes in the concentration of glucose in the lumen.
| S-EPMC1153360 | biostudies-other
Project description:1. The metabolism and transport of glutamine and glucose were investigated in a preparation of rat small intestine perfused through the vascular bed in vitro and in situ. 2. With glucose (7.5mm) or glutamine (4.5mm) in the lumen, approx. 40% of the substrate taken up appears unchanged on the vascular side. When glutamine (1.5mm) is also added to the vascular perfusate, metabolism of glutamine is increased and there is uptake of glutamine from both the vascular bed and lumen. Orientation of substrate (vascular bed or lumen) influences the value of alanine production/glutamine utilization and lactate production/glucose utilization. 3. Deprivation of food and metabolic acidosis have no effect upon the utilization of glutamine by unit length of jejunum. In fed rats, glutamine utilization is 44% of glucose utilization, but in rats deprived of food it is 112% of glucose utilization. 4. Glucose utilization and lactate production are not significantly altered by the presence of glutamine in the vascular bed or lumen. 5. With glucose only in the vascular perfusate, glucose utilization is the same in jejunum and ileum. Glutamine metabolism in the ileum is 28% lower than in the jejunum. 6. Glutamine utilization is dependent on the concentration of glutamine in the vascular perfusate, but is not significantly affected by the absence of glucose. 7. Results are discussed in relation to the role of intestinal glutamine metabolism and with respect to some problems of the transepithelial movement of substrates that are both transported and metabolized.
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Project description:1. Conditions of incubation of everted sacs of rat small intestine were selected to ensure that absorption of d-glucose by mucosal tissue from the incubation medium, intracellular metabolism of the absorbed glucose and transport of glucose through the intact intestinal tissue proceeded linearly with respect to time of incubation within stated time intervals. 2. Under these experimental conditions, steady intracellular concentrations of glucose and lactate were demonstrated. 3. The quantitative translocational and metabolic fate of absorbed glucose was determined under these steady-state conditions. About 25% of glucose absorbed from the external mucosal solution was accumulated (temporarily) within mucosal tissue and about 25% transported through the intact tissue into the external serosal solution; the remainder (about 50%) of the absorbed glucose was metabolized, 90% to lactate and 10% to CO(2). Concomitant respiration rates were comparable with those reported for several other preparations of intestine and were stoicheiometrically in excess of the O(2) metabolism required to account for the production of CO(2) from the absorbed glucose. 4. Water transport through the everted sacs proceeded at an optimum rate under the experimental conditions selected. 5. Some other observations are recorded which influenced the design of the experiments and the interpretation of results; these include the initial physiological state of the animal, the anaesthetic used and the ionic composition of the incubation medium.
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Project description:1. At 30min after oral administration unchanged Synacthen [corticotrophin-(1-24)-tetracosapeptide] was found in the stomach but could not be detected in the lumen of the small intestine of the rat. 2. Synacthen and 41795-Ba {[d-Ser(1), Lys(17), Lys(18)]corticotrophin-(1-18)-octadecapeptide amide} were rapidly metabolized in vitro by both intestinal juice and everted pieces of small intestine. Peptide products were not found either in the intestinal tissue or in the fluid bathing the serosal tissue. 3. Glucose but not O(2) was necessary for the breakdown of the two adrenocorticotrophin analogues by everted tissue. 4. When the products obtained after partial digestion were chromatographically separated and identified, a pattern of breakdown emerged. The N-terminus of Synacthen and the Phe(7)-Arg(8) bond in both analogues were particularly labile. The d-serine N-terminal residue of 41795-Ba conferred a marked protection to aminopeptidase action. 5. The relative susceptibilities of peptide bonds would have been difficult to predict on the basis of existing knowledge of the properties of enzymes of the small intestine.
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Project description:To investigate the effects of the somatostatin analogue, octreotide, on maltose and sucrase activities and expression of glucose transporter type 2 (GLUT2) in obese rat intestinal mucosa.We divided 49 Sprague-Dawley rats into a group of 31 high fat diet-induced obese rats and a group of 18 normal controls. The obese rats were separated into an octreotide treated group of 16 rats and an obese group of 15. The intervention group was injected with octreotide at 40 ?g/kg body weight every 12 h for 8 d. Rat body weight was measured weekly to calculate Lee's index. After euthanization, maltase and sucrase activities in the small intestine were measured by activity assays, and the fasting plasma glucose level was measured. The expression of GLUT2 in small intestinal mucosa was analyzed by immunohistochemistry, reverse transcriptase polymerase chain reaction and Western blotting assays.Body weight, Lee's index, fasting plasma glucose level, maltase activity in small intestinal mucosa, mucosa and apical GLUT2, GLUT2 mRNA and protein expression levels were all significantly higher in the obese group than in the normal control group (605.61 ± 141.00 vs 378.54 ± 111.75, 337.61 ± 10.82 vs 318.73 ± 20.10, 8.60 ± 1.38 vs 7.33 ± 0.70, 156.01 ± 58.81 vs 50.43 ± 30.49, 390 744.2 ± 62 469.21 vs 170 546.50 ± 50 646.14, 26 740.18 ± 3809.60 vs 354.98 ± 57.19, 0.26 ± 0.11 vs 0.07 ± 0.02, and 2.08 ± 0.59 vs 1.27 ± 0.38, respectively, all P < 0.01). Sucrase activity did not differ between the two groups. Octreotide intervention significantly decreased the body weight and fasting plasma glucose level of obese rats (508.27 ± 94.39 vs 605.61 ± 141.00, 7.58 ± 1.51 vs 8.60 ±1.38, respectively, all P < 0.05). The intestinal mucosa and apical GLUT2, expression of GLUT2 mRNA and protein were also significantly lower in the octreotide intervention group than in the obese group (269 975.2 ± 53 730.94 vs 390 744.2 ± 62 469.21, 3758.06 ±364.51 vs 26 740.18 ± 3809.60, 0.08 ± 0.02 vs 0.26 ±0.11, and 1.31 ± 0.27 vs 2.08 ± 0.59, respectively, all P < 0.01).High fat diet-induced obesity is associated with elevated intestinal maltase activity, GLUT2 expression, and permanent apical GLUT2 in the small intestinal mucosa of rats. Octreotide can inhibit these effects.
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Project description:The effect of acute changes in insulin concentrations in vivo on the absorption, transport and metabolism of glucose by rat small intestine in vitro was investigated. Within 2 min of the injection of normal anaesthetized rats with anti-insulin serum, lactate production and glucose metabolism were respectively diminished to 28% and 21% of normal and the conversion of glucose into lactate became quantitative. These changes correlated with the inhibition of two mucosal enzymes, namely the insulin-sensitive enzyme pyruvate dehydrogenase, and phosphofructokinase, which was shown by cross-over measurements to be the rate-limiting enzyme of glycolysis in mucosa. The proportion of glucose translocated unchanged from the luminal perfusate to the serosal medium was simultaneously increased from 45% to 80%. All the changes produced by insulin deficiency were completely reversed with 2 min when antiserum was neutralized by injection of insulin in vivo. The absorption and transport of 3-O-methylglucose were unaffected by insulin. It is concluded that glucose metabolism in rat small intestine is subject to short-term regulation by insulin in vivo and that glucose absorption and transport are regulated indirectly in response to changes in metabolism. Moreover, transport and metabolism compensate in such a way as to deliver the maximal 'effective' amount of glucose to the blood, whether as glucose itself or as lactate for hepatic gluconeogenesis.
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