The Contribution of Intestinal Gluconeogenesis to Glucose Homeostasis Is Low in 2-Day-Old Pigs.

Background: Active gluconeogenesis is essential to maintain blood glucose concentrations in neonatal piglets because of the high glucose requirements after birth. In several adult mammals, the liver, kidney, and possibly the gut may exhibit gluconeogenesis during fasting and insulinopenic conditions. During the postnatal period, the intestine expresses all of the gluconeogenic enzymes, suggesting the potential for gluconeogenesis. Galactose in milk is a potential gluconeogenic precursor for newborns.Objective: Our aim was to quantify the rate of intestinal glucose production from galactose in piglets compared with the overall rate of glucose production.Methods: A single bolus of [U-14C]-galactose was injected into 2-d-old piglets (females and males; mean ± SEM weight: 1.64 ± 0.07 kg) through a gastric catheter. Galactosemia, glycemia, and glucose turnover rate (assessed by monitoring d-[6-3H]-glucose) were monitored. Intestinal glucose production from [U-14C]-galactose was calculated from [U-14C]-glucose appearance in the blood and isotopic dilution. Galactose metabolism was also investigated in vitro in enterocytes isolated from 2-d-old piglets that were incubated with increasing concentrations of galactose.Results: In piglet enterocytes, galactose metabolism was active (mean ± SEM maximum rate of reaction: 2.26 ± 0.45 nmol · min-1 · 106 cells-1) and predominantly oriented toward lactate and pyruvate production (74.0% ± 14.5%) rather than glucose production (26.0% ± 14.5%). In conscious piglets, gastric galactose administration led to an increase in arterial galactosemia (from 0 to 1.0 ± 0.8 mmol/L) and glycemia (35% ± 12%). The initial increase in arterial glycemia after galactose administration was linked to an increase in glucose production rate (33% ± 15%) rather than to a decrease in glucose utilization rate (3% ± 6%). The contribution of intestinal glucose production from galactose was <10% of total glucose production in 2-d-old piglets.Conclusion: Our results indicate that there is a low contribution to glucose homeostasis from intestinal gluconeogenesis in 2-d-old piglets.

Comparative capacities of the pig colon and duodenum for luminal iron absorption.

Iron deficiency is the most common human nutritional disorder in the world. Iron absorptive capacity of the small intestine is known to be much limited and therefore large quantities of iron salts must be used to treat iron deficiency. As a result, significant amounts of iron may reach the large intestine. This study compared the capacities of the small and large intestine to transfer luminal iron to the venous blood in relationship with the expression in epithelial cells of proteins involved in iron absorption using a pig model. Intracaecal injection of iron sulphate corresponding with 2.5 and 5.0 mg elemental iron per kg body mass resulted in modest, transient, but significant (p<0.05) increases in iron concentration in the portal blood plasma. By comparing portal blood plasma iron concentrations following injection in the duodenal and caecal lumen, we calculated that 5 h after injection, iron colonic absorption represented approximately 14% of duodenal absorption. Caecal and proximal colon mucosa accumulated iron to a much lower extent than the duodenal mucosa. Isolated colonocytes were found to express divalent metal transporter (DMT1) and ferritin, but to a lesser extent than the duodenal enterocytes. Ferroportin was highly expressed in colonocytes. In these cells as well as in enterocytes ferroportin was found to be glycosylated. In short term experiments and at a concentration in the range of that measured in the aqueous phases recovered from the large intestine luminal content after iron injection, iron sulphate did not alter colonocyte viability. We concluded that the colonic epithelial cells that express proteins involved in iron absorption are able to transfer luminal iron to the venous blood even if its relative participation in the overall intestinal absorption appears to be modest under our experimental conditions.

In vivo treatment by diallyl disulfide increases histone acetylation in rat colonocytes.

Diallyl disulfide (DADS) is an organosulfur compound from garlic which exhibits various anticarcinogenic properties including inhibition of tumor cell proliferation. DADS antiproliferative effects were previously associated with an increase in histone acetylation in two human tumor colon cell lines, suggesting that DADS-induced histone hyperacetylation could be one of the mechanisms involved in its protective properties on colon carcinogenesis. The effects of DADS on histone H4 and H3 acetylation levels were investigated in vivo in colonocytes isolated from non-tumoral rat. Administrated by intracaecal perfusion or gavage, DADS increases histone H4 and H3 acetylation in colonocytes. Moreover, data generated using cDNA expression arrays suggest that DADS could modulate the expression of a subset of genes. These results suggest the involvement of histone acetylation in modulation of gene expression by DADS in normal rat colonocytes, which might play a role in its biological effects as well as in its anticarcinogenic properties in vivo.

Different activation patterns of rat xenobiotic metabolism genes by two constituents of garlic.

Diallyl sulfide (DAS) and diallyl disulfide (DADS) are natural components that could account for the anticarcinogenic properties of garlic, at least in part, through the activation of xenobiotic detoxifying metabolism. The aim of this work was to describe the effect of DAS and DADS on xenobiotic-related gene expressions and to study molecular mechanisms relaying DAS effect. We describe the different effects of DAS and DADS on hepatic CYP2B1/2, CYP3A and epoxide hydrolase (EpH) mRNAs in rats, in terms of activation profile, doses and kinetics. The activation profile varied with the mode of chemical administration, i.e. gastric infusion or intraperitoneal (i.p.) injection. Using gastric infusion, DAS and DADS proved different efficiencies at enhancing the mRNA level of the three drug-metabolizing enzymes. After an i.p. administration, we observed a specific activation of CYP2B1/2 gene by DAS. The DAS-mediated CYP2B1/2 activation occurred at transcriptional level and through an okadaic acid-sensitive pathway. In rat livers, a short sequence (NR1) derived from the CYP2B1/2 promoter was stimulated by DAS and we observed a nuclear accumulation of a DNA-protein complex binding NR1. Because constitutively activated receptor (CAR) is a major transcription factor driving the xenobiotic-induced stimulation of CYP2B1/2 through NR1, the role of CAR as a preferential mediator of DAS effect is discussed.

Changes induced in colonocytes by extensive intestinal resection in rats.

After massive intestinal resection, physiological compensatory events occur in the remnant small bowel and in the colon. The aim of our work was to study the propensity of the colon to evolve after a massive small bowel resection in rats. The resected group, where 80% of the small bowel length was removed, was compared with sham-operated rats (transected). During the 7 postoperative days, rats were fed orally or they received an elemental nutrition through a gastric catheter. PepT1 and NHE3 mRNAs encoding apical membrane transporters were not modified in the present experiment. However, two unexpected genes (I-FABP and UroR) were up-regulated in the colon following intestinal resection. These modifications occurred without an imbalance of cell cycle protein content and in a context of low short-chain fatty acid production.

Enterocyte metabolism during early adaptation after extensive intestinal resection in a rat model.

OBJECTIVE: A better knowledge of intestinal adaptation after resection is required to improve the nutritional support that is given to patients. The aim of this study was to understand the metabolic changes underlying early adaptation after massive intestinal resection. METHODS: Rats were assigned to either 80% intestinal resection or transection. All animals received the same intragastric nutrition. On day 8, plasma glutamine turnover was measured. Substrate use was determined on isolated enterocytes that were incubated in the presence of D-[U-(14)C] glucose (2 mmol/L), L-[U-(14)C] glutamine (2 mmol/L), L-[U-(14)C] arginine (1 mmol/L), or L-[1-(14)C] ornithine (1 mmol/L). RESULTS: Plasma glutamine turnover was similar in both groups. The rate of enterocyte glutamine use was significantly increased in the resection group, although the maximal glutaminase activity was unchanged. Glutathione generation was enhanced 3-fold in remnant intestine as compared with transected intestine (P <.05). L-ornithine decarboxylation was increased markedly in resected animals (P <.05), without any detectable change of maximal ornithine decarboxylase activity. CONCLUSION: The early phase of intestinal adaptation after resection induces changes in enterocyte glutamine and ornithine metabolism that may be related, in part, to increased de novo polyamine synthesis. This observation suggests that a supplementation of artificial nutrition by nutrients that lead to the generation of trophic agents may be of potential interest.

Luminal fermentation and colonocyte metabolism in a rat model of enteral nutrition.

Large intestinal fermentation and nutrient metabolism in colonocytes were investigated in a rat model of enteral feeding. Male Wistar rats (240-280 g) were submitted to 7 or 14 days of treatment: intragastric feeding (elemental formula) versus oral feeding (isocaloric and isonitrogenous diet, containing 5% purified cellulose) in the control group. Fermentation products and bacterial populations were analyzed in cecal contents. Colonic cells were isolated and tested for their capacities to metabolize [1-(14)C] butyrate and [U-(14)C]glutamine. After 7 days of enteral nutrition, short-chain fatty acid concentrations represented 52% of those measured in the control group, but colonocyte metabolism remained unchanged. After 14 days of enteral nutrition, short-chain fatty acid concentrations were still decreasing, although bacterial counts remained unchanged. In parallel, ammonia and lactate concentrations were significantly increased. The capacities to utilize butyrate and glutamine in colonocytes were only slightly affected. However, there was a dramatic increase in the ratio of beta-OH-butyrate to acetoacetate fluxes, suggesting a more reduced redox mitochondrial state associated with enteral feeding.

Diallyl disulfide increases rat h-ferritin, L-ferritin and transferrin receptor genes in vitro in hepatic cells and in vivo in liver.

Of the oil-soluble organosulfur compounds derived from garlic, diallyl disulfide (DADS) is one of the most abundant. We examined the effect of DADS on gene expression in rat liver. By suppressive subtractive hybridization, we identified the heavy (H)-ferritin gene as a DADS-stimulated gene in the rat liver epithelial (REL) cells. DADS stimulation of H- and L (light)-ferritin mRNA was analyzed in REL cells and in rat liver. Incubation of the REL cells in 10 micro mol/L DADS for 4 h increased H-ferritin 1.9 +/- 0.2-fold, n = 3) and light(L)-ferritin mRNA 1.5 +/- 0.2-fold, n = 3). Stimulation did not occur in the presence of an inhibitor of transcription, actinomycin D. Stimulation of ferritin at the RNA and protein levels was also found in rats administered a DADS-enriched oil solution intragastrically. There was a 3 +/- 1.1-fold increase in H- and 3 +/- 0.14-fold increase for L-ferritin mRNA 24 h after the end of the infusion in the presence of DADS, (n = 3). The expression of the transferrin receptor, an iron transporter, was also enhanced by DADS in rat liver. In conclusion, our data suggest that DADS could modify iron homeostasis through the modulation of ferritin and transferrin receptor gene expression.