Effects of hypoxia on the development of intestinal enzymes in neonatal and juvenile rats

Hypoxia in the neonate is known to alter the activity of hepatic and pancreatic enzymes involved in lipid and carbohydrate metabolism. The purpose of this study was to evaluate the effect of neonatal hypoxia on the activity of intestinal enzymes, and to determine whether the administration of glucocorticoids to neonates can mimic the effects of hypoxia. Hypoxia in neonatal rats (0-7 days) increased protein content, and lactase and maltase activity in the duodenal and the jejunal segments of the small intestine compared with normoxic controls. Hypoxia in juvenile rats (28-35 days) did not change these enzymes. Two weeks after returning hypoxic (0-7 days) pups to normoxia, their body weight remained lower than the age-matched controls. In the group recovering from hypoxia, sucrase, maltase, and leucine aminopeptidase activities were lower in the duodenal and the jejunal segment. Compared with controls, LDH activity was lower only in the jejunal intestine in the group recovering from hypoxia. All enzyme activities returned to control levels 3 weeks after recovery. Neonatal rats treated with dexamethasone had a decrease in body weight, but increases in sucrase and maltase activity in both the duodenal and the jejunal segment. Hypoxia in newborn rats caused a delayed maturation of small intestinal enzymes. Increases in serum glucocorticoids after hypoxic exposure probably do not play a major role in the delayed maturation of the disaccharidase activity in the small intestine.     

Effect of prostaglandin E2 on the small intestine of indomethacin-treated rats

In the present study, the protective effect of PGE2 on intestinal damage in indomethacin-treated adult rats was investigated. Ileal integrity was evaluated making use of different biochemical and histological parameters: activities of sucrase, maltase and diamine oxidase; concentrations of DNA, putrescine, spermidine and spermine; incorporation of 3H-thymidine into DNA; mitotic index and mucosal thickness. Results expressed per g of mucosal weight, showed that: maltase and diamine oxidase activities as well as DNA, spermidine and spermine concentrations decreased markedly in indomethacin-treated rats when compared to control rats; the decrease of maltase activity as well as DNA, spermidine and spermine concentration was less pronounced in PGE2-treated rats when compared to indomethacin-treated rats; 3H-thymidine incorporation into DNA and mitotic index values showed no significant variation in the course of different treatments; mucosal thickness increased strongly, in PGE2-protected rats. We suggest that PGE2 could protect the rat's intestinal mucosa against the effects of indomethacin through a trophic action on intestinal villi.     

Serum glucose and insulin response in rats administered with sucrose or starch containing adenosine, inosine or cytosine

Blood glucose and insulin responses and gastric emptying were examined in rats intubated with sucrose or soluble starch that contained adenosine, inosine and cytosine. The increase in serum glucose and insulin levels in the rats following loading with sucrose (2.5 g/kg of body weight) or soluble starch (1.875 g/kg of body weight) was significantly reduced by the administration of adenosine, inosine and cytosine (0.0625-0.125 g/kg of body weight). The gastric emptying rates were only marginally affected by the nucleoside administration. The activities of sucrase, maltase, isomaltase and glucoamylase in a crude preparation from the small intestinal mucosa of rats were mildly inhibited by the nucleosides. The decrease in blood glucose and insulin levels may have been in response to a decrease in glucose absorption caused by the inhibiting effect of the nucleosides on the mucosal enzymes that digest sucrose, maltose, and malto- and isomalto-oligosaccharides.     

Effect of somatostatin on small intestine enzyme activities in rat and chick

The influence of somatostatin injection on intestinal disaccharidase and alkaline phosphatase activity in rat and chick was investigated. Disaccharidase and alkaline phosphatase activities of rat and chick homogenates were not modified. In rat the activities of mucosal brush-border maltase and sucrase were significantly increased. In chick brush-border a significant increase of duodenal mucosal activity and duodenal and jejunal sucrase activity is observed.     

Inhibitory effects of somatostatin on growth and differentiation in cultured intestinal mucosa

The effect of somatostatin on mucosal DNA, protein and brush border enzymes was studied in organ cultured rabbit jejunum and ileum. Compared to control cultures, somatostatin reduced the biopsy DNA and protein content in parallel in the jejunum, but was ineffective in the ileum. This was probably due to a direct growth inhibition, since DNA and brush border enzyme activity from desquamated cells in the postculture medium were unaffected. In addition, a direct inhibition of jejunal villous cell differentiation by somatostatin was reflected in a significant decrease of sucrase, maltase and alkaline phosphatase activity. In the ileum, only the specific activity of alkaline phosphatase was reduced. The key enzyme of cholesterol synthesis, HMG-CoA-reductase, was measured as an intracellular enzyme control and was not influenced by the hormone. The high somatostatin concentrations necessary to achieve the effects are not an artefact of hormone degradation during culture, as shown by radioimmunoassay, and suggest a local or "paracrine" rather than systemic, inhibitory action of somatostatin on intestinal growth and differentiation.     

Disaccharidase activities after jejunoileal bypass in rat

Digestive enzymatic activities (maltase, lactase and sucrase) have been determined in the intestinal mucosa of rats subjected to a jejunoileal bypass of 45 cm. The weight and protein content of the mucosa (mg/cm) were significantly decreased in the bypassed segment and significantly increased in the unbypassed segment, as compared to control rats. Maltase, lactase and sucrase specific (U/g protein) and total activity (U/cm intestine) were significantly decreased in the bypassed jejunum, compared to sham-operated rats. In the ileum, maltase specific and total activities increased in bypassed animals while the lactase and sucrase activities remained unchanged.     

Role of temporary intestinal brush border dysfunction inCampylobacter jejuni diarrhea

The pathophysiologic effects ofCampylobacterjejuni on weanling ferrets were investigated by assessing jejunal disaccharidase activities, glucose and theophylline stimulation of jejunal mucosal ion transport, fecal levels of reducing sugars, and histologic appearance of the gut. Compared with uninoculated controls, ferrets at the peak ofCampylobacter-induced watery diarrhea exhibited two- to threefold reductions in sucrase, maltase, and lactase activity, a sixfold lower short-circuit current response to glucose stimulation, and a twofold higher response to theophylline stimulation, plus a striking increase in fecal levels of reducing sugars. These physiologic alterations rapidly returned to normal as diarrhea subsided. Jejunal epithelial cells of all diarrheic animals appeared morphologically normal by light microscopy. Passively immunized kits, heavily colonized but not diarrheic, were indistinguishable from controls in every assessment. These observations suggest that (i)Campylobacterjejuni exerts its pathophysiologic effect primarily by inducing a transient depression of intestinal brush border function and (ii) such effects can be prevented by humoral antibodies.     

Effect of pentagastrin, secretin and cholecystokinin on growth and differentiation in organ cultured rabbit small intestine

The effect of pentagastrin, secretin and cholecystokinin on biochemical parameters of mucosal growth and differentiation was studied in organ cultured rabbit jejunum and ileum. Pentagastrin at 0.05-5.0 microgram/ml did not affect DNA content of the biopsy, but led to a significant decrease of sucrase and alkaline phosphatase activity in the ileum. Secretin prompted a significant decrease of DNA and protein in the ileum at a level of 10(-7) and 10(-5) M, but had no effect in the jejunum. Of the brush border enzymes, sucrase and alkaline phosphatase were suppressed in both parts of the intestine both with respect to specific activity and total biopsy content. Cholecystokinin, like pentagastrin, did not influence DNA or protein content, but reduced sucrase, maltase and alkaline phosphatase activity. HMG-CoA reductase, the key enzyme of cholesterol synthesis, was not significantly affected by any of the three hormones tested. When brush border enzymes or DNA from desquamated cells were measured in the post-culture medium, no consistent effect of any gastrointestinal hormone was apparent. The present study demonstrates a direct "antitrophic" effect of secretin in cultured mucosa. Pentagastrin and cholecystokinin did not influence mucosal DNA content in vitro but apparently inhibited villus cell differentiation.     

Caffeoylsophorose, a new natural alpha-glucosidase inhibitor, from red vinegar by fermented purple-fleshed sweet potato

The suppressive effect on the postprandial blood glucose rise through alpha-glucosidase (AGH) inhibition was investigated in this study in order to clarify an antihyperglycemic function of 6-O-caffeoylsophorose (CS) from diacylated anthocyanin. The administration of CS (100 mg/kg) following maltose (2 g/kg) to Sprague-Dawley rats resulted in the maximal blood glucose level after 30 min being significantly decreased by 11.1% compared to the control. A reduction in the serum insulin secretion was also observed in parallel to the decrease in blood glucose level. No blood glucose change was apparent when sucrose or glucose was ingested, suggesting that the antihyperglycemic effect of CS was achieved by maltase inhibition, rather than by sucrase or glucose transport inhibition. An AGH inhibitory assay demonstrated that the non-competitive maltase inhibition of CS was partly due to acylation by phenolic acid with sugar, the presence of hydroxyl groups in the aromatic ring, and the presence of an unsaturated alkyl chain in the acylated moiety.     

Biochemical analysis of jejunal brush border membrane of golden hamster: pathogenic modulations due to ancylostomiasis.

The common hookworm (Ancylostoma ceylanicum) infection of humans was studied in golden hamsters model system. Significant biochemical modulations were observed in hamster jejunal brush border membrane (BBM), the primary site of infection. Analysis of BBM at the peak of infection (3-weeks) revealed a marked decrease in the activities of sucrase, lactase and maltase, while activities of alkaline phosphatase, (Ca2+ + Mg2+)-ATPase and gamma-glutamyl transpeptidase were increased. Kinetic studies conducted with maltase, a superficially localised enzyme of jejunal BBM, revealed loss of enzyme active site during the infection. Among other constituents, the levels of cholesterol and triglycerides were significantly decreased with slight increase in phospholipid content in the infected animals. The hookworm infection also caused a decline in total hexose content indicating an altered membrane glycocalyx. Conversely, there was significant enhancement of hydroxyproline and sialic acid contents. SDS-PAGE analysis showed an enhancement in both low and high molecular weight proteins in jejunal BBM preparations of the infected group. Gel electrophoresis of glycoproteins further revealed the appearance of two additional peaks in the low molecular weight region and concomitant disappearance of a peak in the high molecular weight region. These results strongly support the view that the hookworm infection causes severe damage not to the site of attachment alone but also to the entire cell lining of the jejunum and therefore could influence overall digestion and absorption.     

Suppressive effect of a hot water extract of adzuki beans (Vigna angularis) on hyperglycemia after sucrose loading in mice and diabetic rats

A hot water extract obtained by boiling adzuki beans (Vigna angularis) to produce bean paste for Japanese cake showed inhibitory activity against alpha-glucosidase, alpha-amylase, maltase, sucrase, and isomaltase after HP-20 column chromatography. The IC(50) values for each hydrolylase were 0.78 mg/ml (alpha-amylase), 2.45 mg/ml (maltase), 5.37 mg/ml (sucrase), and 1.75 mg/ml (isomaltase). The active fraction showed potential hypoglycemic activity in both normal mice and streptozotocin (STZ)-induced diabetic rats after an oral administration of sucrose, but did not show any effect on the blood glucose concentration after glucose administration, suggesting that the active fraction suppressed the postprandial blood glucose level by inhibiting alpha-glucosidase and alpha-amylase, irrespective of the endogenous blood insulin level.     

The effect of dexamethasone on the development of rat intestinal brush border enzymes in organ culture

The effect of dexamethasone on the evolution pattern of brush border enzymes was examined in the rat jejunum cultured in vitro at different postnatal stages (4 to 21 days). Enzymic activities were analyzed in purified brush border membranes isolated from noncultured intestine and from explants cultured for 24 and 48 hr. The data obtained from this study indicated that dexamethasone exhibits two types of effects on the cultured intestinal tissue: (1) a nonspecific but protective effect against the drastic drop of all enzyme activities as well as against a loss of villus cells observed in control cultures, and (2) a direct and specific effect on precocious induction of sucrase and on stimulation of maltase activity. The SDS-polyacrylamide gel patterns of brush border membrane proteins showed that in the 6-day-old intestine, appearance of sucrase as well as stimulation of maltase activities elicited by dexamethasone were accompanied by a simultaneous appearance or enhancement of the corresponding protein bands. Furthermore, the radioactivity peaks on gels due to the incorporation of ¹⁴C-valine and of ¹⁴C-fucose indicated that dexamethasone induces the synthesis of new proteins or at least the glycosylation of preexisting proteins which may lead to the formation of active maltase and sucrase molecules.     

Insulin-like growth factor I and glucagon-like peptide-2 responses to fasting followed by controlled or ad libitum refeeding in rats

Luminal nutrients stimulate structural and functional regeneration in the intestine through mechanisms thought to involve insulin-like growth factor I (IGF-I) and glucagon-like peptide-2 (GLP-2). We investigated the relationship between IGF-I and GLP-2 responses and mucosal growth in rats fasted for 48 h and then refed for 2 or 4 days by continuous intravenous or intragastric infusion or ad libitum feeding. Fasting induced significant decreases in body weight, plasma concentrations of IGF-I and bioactive GLP-2, jejunal mucosal cellularity (mass, protein, DNA, and villus height), IGF-I mRNA, and ileal proglucagon mRNA. Plasma IGF-I concentration was restored to fed levels with 2 days of ad libitum refeeding but not with 4 days of intravenous or intragastric refeeding. Administration of an inhibitor of endogenous GLP-2 (rat GLP-2 3-33) during ad libitum refeeding partially attenuated mucosal growth and prevented the increase in plasma IGF-I to fed levels; however, plasma GLP-2 and jejunal IGF-I mRNA were restored to fed levels. Intragastric refeeding restored intestinal cellularity and functional capacity (sucrase activity and sodium-glucose transporter-1 expression) to fed levels, whereas intravenous refeeding had no effect. Intestinal regeneration after 4 days of intragastric or 2 days of ad libitum refeeding was positively associated with increases in plasma concentrations of GLP-2 and jejunal IGF-I mRNA. These data suggest that luminal nutrients stimulate intestinal growth, in part, by increased expression of both GLP-2 and IGF-I.     

IGF alters jejunal glucose transporter expression and serum glucose levels in immature rats

Milk-borne insulin-like growth factors (IGFs) enhance nutrient absorption in the immature intestine, which is characterized by low levels of glucose oxidation. We therefore hypothesized that feeding a rat milk substitute (RMS) devoid of growth factors to rat pups would lower serum glucose levels relative to dam-fed control rats and that supplementation of RMS with physiological doses of either IGF-I or IGF-II would normalize serum glucose levels via increased jejunal glucose transporter 2 (GLUT2) and high-affinity Na(+)-glucose cotransporter (SGLT1) expression. We found lower serum glucose concentrations in RMS-fed pups; in contrast, serum glucose levels in the IGF-supplemented pups were similar to those of dam-fed controls. RT-PCR and laser scanning confocal microscopy similarly demonstrated that IGF supplementation increased expression of jejunal glucose transporters. Further experiments demonstrated that IGF supplementation altered mRNA levels of key mitochondrial enzymes without altering jejunal lactase activity. We conclude that IGF-I and IGF-II supplementation increases serum glucose levels in the immature rat pup fed artificial formula and alters gene expression of the jejunal glucose transporters.     

IGF-I treatment facilitates transition from parenteral to enteral nutrition in rats with short bowel syndrome

The goal of growth factor treatment in patients with short bowel syndrome (SBS) is to facilitate transition from parenteral to enteral feedings. Ideal use of growth factors would be acute treatment that produces sustained effects. We investigated the ability of acute insulin-like growth factor I (IGF-I) treatment to facilitate weaning from total parenteral nutrition (TPN) to enteral feeding in a rat model of SBS. After a 60% jejunoileal resection + cecectomy, rats treated with IGF-I or vehicle were maintained exclusively with TPN for 4 days and transitioned to oral feeding. TPN and IGF-I were stopped 7 days after resection, and rats were maintained with oral feeding for 10 more days. In IGF-I-treated rats, serum concentration of IGF-I and final body weight were significantly greater because of a proportionate increase in carcass lean body mass than in vehicle-treated rats. Acute IGF-I treatment induced sustained jejunal hyperplasia on the basis of significantly greater concentrations of jejunal mucosal protein and DNA without a change in histology or sucrase activity. These results demonstrate that acute IGF-I facilitates weaning from parenteral to enteral nutrition in association with maintenance of a greater body weight and serum IGF-I concentration in rats with SBS.     

Ontogenesis of intestine morphology and intestinal disaccharidases in chickens (Gallus gallus) fed contrasting purified diets

Two groups of growing posthatching Cornish x Rock cross chickens were fed with either a carbohydrate-containing (52.5%) or a carbohydrate-free diet. At 36 days after hatching some of the chicks in each group were shifted to the opposite diet. Chickens fed on a carbohydrate-containing diet grew faster and achieved higher asymptotic masses than chickens fed on a carbohydrate-free diet. Chickens fed on a carbohydrate-free diet had longer intestines and larger intestinal areas than chickens of the same mass fed on a carbohydrate-containing diet. In both groups sucrase and maltase activity (standardized by either intestinal area or mass) increased from day 1 to approximately day 17. After day 17, chickens fed on a carbohydrate-containing diet exhibited 1.8 and 1.9 times higher sucrase and maltase activities per unit intestinal area, respectively, than chickens fed on a carbohydrate-free diet. Analysis of covariance was used to estimate the contribution of sucrase and the sucrase-independent maltases to maltase activity, and to estimate the effect of diet on the sucrase-independent maltases. Sucrase contributed 80% and 75% of the maltase activity in carbohydrate and carbohydrate-free fed chickens, respectively. Chickens shifted from a carbohydrate-free to a carbohydrate diet converged in gross intestinal morphology and intestinal sucrase and maltase levels with carbohydrate-fed chickens within 8 days. Chickens shifted from carbohydrate to carbohydrate-free diets, in contrast, did not show appreciable changes in intestinal length and after 8 days had not reduced levels of sucrase and maltase to those of chickens fed on the carbohydrate-free diet. A comparison of integrated maltase intestinal activity with published data on glucose uptake showed that the ratio of maltose hydrolysis to glucose uptake seemed to be about 7 and to remain relatively invariant during ontogeny. Because so little is known about the interaction between hydrolysis and uptake in vivo, it is difficult to determine if this relatively high ratio represents excess hydrolytic capacity or if it is needed to provide high lumenal glucose concentrations that maximize uptake.Abbreviations m body mass - K _m Michaelis constant - K _m ^* apparent Michaelis constant - GI gastro-intestinal     

Organ culture of suckling rat intestine: comparative study of various hormones on brush border enzymes

Jejunal mucosa of 6 d-old rats were cultured for 24 and 48 h in the presence of thyroxine, insulin, pentagastrin, glucagon, epidermal growth factor (EGF) or dibutyryl-A-3:5-MP cyclic with or without dexamethasone (DX). The enzymes were assayed on the purified brush borders. The various agents added alone to the basic culture medium had no effect with the exception of DX on the levels of enzyme activities. Dexamethasone alone induced sucrase, stimulated maltase, and protected other brush border enzyme activities (aminopeptidase, lactase, and alkaline phosphatase). When added to DX-supplemented medium, only the following factors modified the levels of enzymatic activities observed with DX alone. Insulin (10(-6) M) increased maltase, alkaline phosphatase, and lactase activity to a greater extent than DX at 24 h culture, the effect being maintained at 48 h on alkaline phosphatase only. At 48 h culture, both EGF (10(-8) M) and dbcAMP (10(-3) M) decreased DX-induced sucrase activity. The latter agent also depressed DX-stimulated aminopeptidase activity.     

Bypassing the duodenum does not improve insulin resistance associated with diet-induced obesity in rodents

Roux-en-y gastric bypass (RYGB) surgery rapidly improves glucose tolerance and reverses insulin resistance in obese patients. It has been hypothesized that this effect is mediated by the diversion of nutrients from the proximal small intestine. We utilized duodenal-jejunal bypass (DJB) as a modification of gastric bypass to determine the effect of nutrient diversion from the foregut without gastric restriction on insulin resistance in obese rats. The effects of DJB or Sham surgery on glucose homeostasis were determined in both high-fat-fed Long-Evans and Wistar rats. Body weight and food intake were measured weekly postoperatively, and body composition was monitored before and after surgery. Glucose tolerance was tested before and as early as 1 month postoperation; additionally, in Wistar rats, insulin sensitivity was determined by a hyperinsulinemic-euglycemic clamp (HIEC). DJB did not affect body weight, body composition, glucose tolerance, or insulin concentrations over the period of the study. The average glucose infusion rate (GIR) during the HIEC was 6.2 ± 1.16 mg/kg/min for Sham rats compared to 7.2 ± 1.71 mg/kg/min for DJB rats (P = 0.62), and neither endogenous glucose production (EGP; P = 0.81) nor glucose utilization (glucose disappearance (R(d)), P = 0.59) differed between DJB and Sham rats. DJB does not affect insulin resistance induced by a high-fat diet in Long-Evans and Wistar rats. These data suggest that duodenal bypass alone is an insufficient mechanism to alter insulin sensitivity independent of weight loss in obese, nondiabetic rodents.     

Effects of diabetes on development of small intestinal enzymes of infant rats

The effect of streptozotocin (SZ) on the development of small intestinal enzymes in postnatal rat pups was studied. SZ was injected ip on Day 10 and, if necessary, again on Day 12. On Days 15, 18, and 21, one pup from each group (including a vehicle-injected control (C) group) was decapitated under conditions which minimized stress. Plasma glucose, insulin (IRI), and corticosterone were measured, as were pancreatic IRI, liver glycogen, and liver membrane binding of IRI. Small intestinal segments were processed and analyzed for sucrase, lactase, maltase, and ileal acid beta-galactosidase activities. Our results indicate that plasma glucocorticoid levels remained virtually constant in both SZ and C groups, while the ontogenic profiles of sucrase and maltase in SZ rats were shifted toward an earlier appearance and a precocious maturation. Circulating levels of IRI were not reduced significantly by SZ despite the fact that pancreatic IRI was decreased 95%. Jejunal lactase, unlike data reported for diabetic rats, was not affected by SZ diabetes. Also, acid beta-galactosidase was unaltered in the SZ rat pups. It is concluded that possibly the elevated disaccharidases seen in diabetic postnatal rat pups are the direct effect of elevated blood glucose. If so, the SZ rat pup model may be a useful tool with which to study effects of glucose on intestinal enzymes in the absence of changes in plasma insulin.     

Effects of dietary L-arginine supplementation on serum lipids and intestinal enzyme activities in diabetic rats

We investigated whether dietary supplementation with L-arginine, the endogenous precursor of nitric oxide, might affect serum lipid levels and activities of intestinal mucosa enzymes in animals, in which diabetes was induced by administration of streptozotocin. Control and diabetic rats were fed diets with or without 2% L-arginine supplementation for 4 weeks. Diabetic rats had significantly higher concentrations of serum triglycerides and LDL-cholesterol than control rats. These alterations were partially reduced by L-arginine supplementation. Experimental diabetes did not influence the lactase and leucine aminopeptidase activity in the intestine, but the activity of alkaline phosphatase was increased. Furthermore, activities of maltase and sucrase in the intestinal mucosa were elevated in streptozotocin-induced diabetic rats and were restored to control levels after dietary L-arginine supplementation. On the basis of the present experimental evidence, dietary L-arginine supplementation appears to affect the metabolism of lipoproteins and might alleviate some gastrointestinal dysfunctions, commonly seen in diabetes mellitus.