Cellular adaptation of the rat small intestine after proximal enterectomy: changes in microvillous enzymes and in the secretory component of immunoglobulins

To investigate the adaptation of functions expressed by the villous and crypt cell of the intestinal mucosa after intestinal resection, a 50% proximal enterectomy or a single transection was performed in 16 growing rats weighing 175-200 g. Ten days following the enterectomy, we determined the mucosal mass parameters (weight, protein, and DNA content), the activity of microvillous enzymes (lactase, sucrase, and aminopeptidase) in villus cells, and the concentration of the secretory component of immunoglobulins in crypt cells isolated from the proximal intestinal remnant. Mucosal hyperplasia was attested by the finding that mucosal weight, protein, and DNA content per cm of intestinal length were significantly (p less than 0.01) higher (+29 to +48%) in the resected group than in transected controls. The specific activity of lactase, sucrase, and aminopeptidase were significantly (p less than 0.05) lower (-23 to -56%) in villous cells isolated from the intestinal remnant of resected rats compared to controls. Sucrase activity was depressed in each cell fraction of the entire villous-crypt unit resulting in a lower villous to crypt gradient of enzyme activity. Km for the enzyme determined in villous cells was similar in both groups but the Vmax was reduced proportionally to the enzyme activity in the resected group indicating less enzyme per cell. By contrast, the concentration of secretory component measured by an immunoradiometric assay in both villous and crypt cells was significantly (p less than 0.05) increased (+37 to 45%) following proximal enterectomy. Our data indicate that the response of the epithelial cell to intestinal resection varies according to the metabolic function and that the mechanism of adaptation at the cellular level is complex.     

Intestinal development and fatty acid binding protein activity of newborn pigs fed colostrum or milk.

Newborn pigs (n = 20) were gavage-fed sow's colostrum, defatted colostrum, milk, defatted milk or a 5% lactose solution over 24 h in order to evaluate effects on growth and functional differentiation of small intestine. Colostrum-fed pigs had greater (p less than 0.01) mucosal mass in the proximal half of the small intestine than did the milk- or lactose-fed groups. Total fatty acid binding protein (FABP) activity and FABP activity per mg DNA in proximal intestines of colostrum-fed pigs exceeded that for the lactose group. FABP activities (per g mucosa or mg soluble protein) were greater (p less than 0.01) in the proximal segments of small intestines of pigs fed whole versus the corresponding defatted secretion. These results indicate that the feeding of colostrum specifically augments perinatal intestinal growth and differentiation as manifested by increased cellular hypertrophy and FABP activity. Milk lipid and unidentified factor(s) enriched in colostrum are inducers of intestinal FABP activity.     

Effect of bombesin on the development of the neonatal rabbit gastrointestinal tract.

The effect of bombesin on the postnatal development of the gastrointestinal tract was examined in New Zealand white rabbits. Bombesin (1.25, 12.5, 30 micrograms/kg body weight) or vehicle was administered intraperitoneally to suckling rabbits for 13 days starting on day 4 of life. The animals were killed at day 17. There was no significant effect of bombesin at doses of 1.25 or 12.5 micrograms/kg in any region of the gut studied. Bombesin administered at 30 micrograms/kg induced a widespread trophic effect in the gastrointestinal tract characterized by significant increases in the wet weight of the stomach, liver and whole small intestine, as well as in 10-cm segments of the proximal, middle, and distal small intestine. There was also a significant increase in the mucosal weight of 10-cm segments of the proximal, middle and distal small intestine, and the colon in the bombesin-treated group. Bombesin significantly increased the protein and DNA contents of the liver, the fundus of stomach, all segments of the small intestine and the distal colon. Maximal stimulation was seen in DNA content, suggesting that bombesin has a primarily hyperplastic effect. Bombesin increased the activities of small intestinal sucrase and maltase but not lactase. Bombesin did not alter hepatic glucokinase activity. These findings suggest that bombesin can promote the growth of the neonatal rabbit gastrointestinal tract and liver.     

Effects of short-term growth hormone therapy in rats undergoing 75% small intestinal resection.

Thirty 250-g male rats underwent 75% small intestinal resection and received s.c. injections of water [short gut (SG)-control], human growth hormone (hGH) at 0.1 mg/kg/dose [SG-low-dose (LD) GH], or hGH at 1.0 mg/kg/dose [SG-high-dose (HD) GH] every other day for 28 days. Ten additional rats underwent sham operation and received water injections (sham control). After 28 days, SG-control and SG-LDGH rats weighed significantly less than the sham control group; the mean weight of the SG-HDGH group was not different from other groups. Weight per centimeter of the distal ileum was greater in all SG groups compared to the sham control group, and was greater in the SG-HDGH than in the SG-control group. Mean mucosal height of the distal ileum was greater in both SG groups receiving GH than in sham controls. No differences in ileal mucosal DNA content or ileal insulin-like growth factor-1 (IGF-1) content were identified between groups. Mucosal sucrase activity was not increased in hGH-treated rats. Serum calcium and phosphorus concentrations were higher in SG-HDGH rats than in SG-control animals. HDGH increased body weight, distal ileal weight/cm, and mucosal height in rats undergoing 75% small bowel resection. A trend toward normalization of serum calcium, phosphorus, and plasma IGF-1 concentrations was also observed. Further longer-term studies are indicated to learn if GH has a beneficial effect upon gut growth and function in the SG syndrome.     

Effect of dietary nucleosides on growth and maturation of the developing gut in the rat

Dietary nucleoside (DN) as a precursor for nucleic acid synthesis may be important for rapidly dividing cells, since gut epithelial cells have limited capacity for de novo purine and pyrimidine synthesis. We evaluated in a controlled blinded study the effect of added nucleosides, 0.8% by weight, given for 2 weeks, on gut growth and maturation in 20 weanling rats. Mucosal protein and DNA in the proximal intestinal segment were 50% and 77% higher, respectively, in the DN-supplemented group (n = 10; p less than 0.05). Villus height based on cell count was 25% greater in the DN group (p less than 0.05). Maltase activity was significantly greater in proximal, middle, and distal intestinal segments, and the largest increase, 87%, was seen in the proximal gut mucosa. The maltase/lactase ratio was also higher in this segment. Increases in sucrase were less prominent. Lactase was minimally affected. The pattern of change in disaccharidase activity suggests that DN may enhance gut growth and maturation of the intestine in the weanling rat, the effects being more pronounced in the proximal segment. Diets free of nucleosides and nitrogenous bases may have adverse effects on the gut.     

Intestinal resection in the neonatal rat: stimulus for precocious intestinal maturation

To investigate whether intestinal resection accelerates mucosal maturation in suckling rats, macromolecular absorption, sucrase and lactase activity, RNA/DNA ratios, and intestinal morphology were determined 5 days after partial small intestinal resection or intestinal transection in 15-day-old rats. Villous height and crypt depth, lactase and sucrase activity, and RNA/DNA ratios were significantly increased in remaining intestine in animals that underwent surgery. These animals, together with normal control animals, were also gavaged with 100 mg bovine serum albumin, and serum levels were determined after 2.5 h. Mean serum levels of bovine serum albumin were 0.135 +/- 0.034 micrograms/ml/cm of residual intestine after transsection, 0.257 +/- 0.078 micrograms/ml/cm after resection, and 0.404 +/- 0.030 micrograms/ml/cm in controls. These studies demonstrate that intestinal resection during the suckling period of the infant rat results in several morphologic and physiologic changes that resemble precocious maturation of the small intestine.     

Saccharomyces boulardii does not stimulate mucosal hyperplasia after intestinal resection in the rat

BACKGROUND: Polyamines have been shown to be important regulators of the intestinal adaptation process after massive bowel resection. Saccharomyces boulardii is yeast that has the ability to synthesize polyamines. Therefore. S. boulardii may be useful in the treatment of short bowel syndrome. METHODS: Twenty 150-g male Sprague-Dawley rats were subjected to 80% jejunoileal resection. Another 20 animals received transection and closure and served as pair fed controls. One half of the resected rats and one half of the controls were given S. boulardii 25 mg/day. RESULTS: After 2 weeks, mucosal mass (mg/cm bowel) did not differ between treated and non-treated animals despite the presence of a marked resection effect. Mucosal DNA, protein, and sucrase activity likewise did not differ. Subsequently, the experiment was repeated four times the original dose (100 mg/day) and found comparable results. In the proximal bowel, mucosal mass was 92+/-6 mg/cm in treated animals versus 107+/-8 mg/cm in untreated rats. In the distal small bowel, comparable values were 85+/-5 mg/cm and 88+/-4 mg/cm. Again, mucosal DNA, protein, and sucrase activity levels paralleled these results. CONCLUSIONS: Although S. boulardii may stimulate polyamine synthesis, it does not seem to be helpful in augmenting gut adaptation in this animal model of short bowel syndrome.     

Role of dietary protein adaptation at weaning in the development of the rat gastrointestinal tract

To evaluate the role of the quantitative adaptation in dietary protein at weaning in the growth and maturation of the rat gastrointestinal tract, we studied parameters of tissue mass, DNA synthesis, and enzyme activities in suckling pups weaned by day 17 to a semipurified synthetic, isocaloric diet that contained either 8 or 27% casein (controls). Rats of both groups were studied on days 21, 28, and 35 postpartum. On day 21, protein restriction had little effect on mean body weight, wet stomach and liver weight, gut length and colonic, jejunal or ileal mucosal weights per centimeter, whereas on day 35, all these tissue mass parameters were significantly (p less than 0.01 versus controls) depressed in the 8% protein group. DNA and protein content expressed per intestinal segment or per total organ and the protein/DNA ratio paralleled the changes in tissue mass, except that total DNA of the small intestine was decreased by 33% (p less than 0.01 versus controls) in 21-day-old rats with protein restriction. In the same age group, DNA synthesis rate, measured by the incorporation rate of [3H]-thymidine per milligram tissue DNA, was markedly depressed in the small intestine (4-fold decrease; p less than 0.001 versus controls) and in the liver (2-fold decrease; p less than 0.05 versus controls) while in the colon the effect of protein restriction occurred later (day 35).(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of casein versus casein hydrolysate on mucosal adaptation following massive bowel resection in infant rats

Little is known concerning the effects of elemental diets on bowel adaptation following massive resection. Fourteen of 28 Sprague-Dawley rats (40-45 g) were subjected to a 60% jejunoileal resection. Seven of the resected animals and seven sham-operated controls were then placed on a diet containing all protein in the form of casein hydrolysate. The remaining seven resected animals and seven sham-operated controls were placed on a comparable diet in which all the protein was casein. Each control animal was paired with a resected animal. After 2 weeks, unidirectional glucose and leucine transport was determined from intestinal sacs made from the proximal 3 cm and distal 3 cm of the remaining bowel. The midportion was used for the determination of mucosal weight and protein and sucrase content. When expressed as a percent increase over control values per centimeter of bowel, only sucrase levels were significantly elevated in the distal bowel in casein hydrolysate-versus casein-fed animals. The mucosal protein level, mucosal weight, and glucose uptake did not differ from control values when expressed as a percent change. Leucine uptake was significantly decreased in casein hydrolysate-fed animals when compared to that in casein-fed animals in both the proximal and distal bowel, again when expressed as a percent change from the control values. The administration of protein in the form of casein hydrolysate following massive bowel resection does not adversely affect mucosal hyperplasia occurring after resection but may have an adverse effect on the enhancement of amino acid absorption.     

Role of gastrin and cholecystokinin in the ontogenic development of the gastrointestinal tract

The role of gastrin and cholecystokinin (CCK) in postnatal development of the small intestine was examined in infant rabbits. Experimental animals received daily intraperitoneal injections of pentagastrin, 500 micrograms/kg, or CCK-octapeptide, 40 micrograms/kg, starting on day 3 of life. The animals were sacrificed at age 17-18 days. Weight and histologic sections of pancreas, stomach, duodenum, proximal jejunum, and ileum were obtained and mucosal lactase and sucrase activities determined in the intestinal segments. No differences were seen in any of the parameters assessed in pentagastrin-treated animals compared to saline-injected littermate controls. Body weight, weight and morphology of pancreas, stomach and intestinal segments, and enzyme activities did not differ significantly. Na+ transport in proximal jejunum under short-circuited conditions was not altered by pentagastrin. CCK-octapeptide also had no effect on weight or morphology of pancreas, stomach, and duodenum, but did lead to a significant increase in weight of proximal jejunum and ileum. Mucosal enzyme activities and morphometric measurements of villus height and mucosal thickness, however, did not differ significantly between CCK-octapeptide-treated animals and saline-injected littermate controls. The increase in weight of jejunal and ileal segments was reflected by an increase in thickness of the muscle layer. The findings indicate that neither gastrin nor CCK plays a role in the ontogenic development of the small intestine.     

Alterations in postnatal intestinal function during chronic hypoxemia.

Growth failure is a major complication of chronic hypoxemia, as seen in infants and children with cyanotic congenital heart disease. To determine whether chronic hypoxemia during infancy affects the gastrointestinal tract, we examined small intestinal growth and digestive enzyme activities in chronically hypoxemic newborn lambs and in age-matched controls. Chronic hypoxemia was produced by placing an inflatable occluder around the main pulmonary artery and performing a balloon atrial septostomy. Aortic oxygen saturation was reduced to 60-74% for 2 wk, after which the small intestine was removed for analysis. During chronic hypoxemia, somatic growth rate was decreased to 60% of control (hypoxemic, 135 +/- 20 versus control, 216 +/- 26 g/d, p less than 0.02). No differences in caloric intake were found (hypoxemic, 129 +/- 4 versus control, 128 +/- 4 kcal/kg/d). Chronic hypoxemia did not alter small intestinal growth, as measured by jejuno-ileal weight, jejuno-ileal length, mucosal weight, or mucosal protein or DNA contents. However, sp act of lactase, the principal disaccharidase of the infant lamb intestine, were significantly decreased (hypoxemic, 0.08 +/- 0.01 versus control, 0.146 +/- 0.03 units of enzyme activity/mg DNA, p less than 0.05), as were the total small intestinal contents of lactase (hypoxemic, 61.7 +/- 7.0 versus control, 120.6 +/- 21.7 units of enzyme activity, p less than 0.01). There also were decreases in specific and total activities of other digestive enzymes such as maltase, amino-oligopeptidase, and alkaline phosphatase in hypoxemic intestine that did not achieve statistical significance.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of short-term isolated zinc deficiency on intestinal growth and activities of several brush border enzymes in weaning rats

To determine whether zinc has a specific role on intestinal growth and function, three groups of male weanling Sprague-Dawley rats were fed a semipurified zinc-deficient diet: ad libitum fed group received powdered diet and water containing 25 ppm of zinc; force fed (ZN, ZD) groups were fed identical amounts of diet to the ad libitum fed group by intragastric infusion three times per day. The diets were aqueous suspensions made with either deionized water (ZD) or water containing 25 ppm of zinc (ZN), and additional drinking water with (ZN) or without zinc (ZD) was offered ad libitum. Rats were sacrificed after 8 days of feeding. The ZD group showed growth arrest, perioral and periorbital dermal lesions, and abdominal distention within 8 days of feeding. Mucosal DNA, protein, sucrase, maltase, lactase, leucine aminopeptidase, and alkaline phosphatase were significantly decreased in the ZD group, whereas intestinal length, weight, and mucosal weight were unaltered. These results suggest that short-term isolated zinc deficiency impairs growth, digestion, and absorption in the rat small intestine, even in the absence of associated protein calorie malnutrition.     

Histologic findings are not correlated with disaccharidase activities in infants with protracted diarrhea

Histologic assessment as well as information about the disaccharidase activity of the small intestinal mucosa can be useful in the management of patients with small intestinal mucosal damage. In an effort to determine whether the degree of small intestinal mucosal damage would be reflected in a corresponding reduction in disaccharidase activity, we compared small intestinal mucosal histology with the results of disaccharidase activity measured in per oral suction small intestinal biopsies obtained from 21 infants with protracted diarrhea. The degree of small intestinal mucosal damage was graded using a subjective score (i.e., 0 to 4+ damage) by a pathologist (P) and by a computer-assisted digitizing system (to assess villus surface area, VSA, and villus/crypt ratio, V/C) in a blinded fashion. The mean (+/- SD) age of the infants was 2.5 +/- 1.5 months, and the duration of diarrhea was 25.2 +/- 11.5 days. There was good correlation between the results obtained from the digitizing system and from the pathologist: VSA versus P, r = 0.695; V/C versus P, r = 0.791; p = 0.0004. All infants demonstrated some degree of small intestinal mucosal damage. The mean (+/- SD) values for P, VSA, and V/C were 2.2 +/- 1.3, 2.9 +/- 0.9, and 0.9 +/- 0.5, respectively. The mean values for lactase, sucrase, and maltase were 17.1 +/- 17.0, 71.1 +/- 54.0, and 224.3 +/- 233 mumol/min/g protein, respectively. No correlation was observed between the histologic scoring results and lactase, sucrase, or maltase measurements. Expressing the disaccharidase activities per unit wet weight of tissue did not improve the correlations. Log transformation of the data also failed to improve the correlations.(ABSTRACT TRUNCATED AT 250 WORDS)     

The effect of leptin on intestinal recovery following ischemia-reperfusion injury in a rat

Recent evidence suggests that the adipose tissue derived cytokine leptin (LEP) is involved in the modulation of growth and differentiation of normal small intestine. The purpose of the present study was to examine the effect of leptin on enterocyte turnover and intestinal recovery after ischemia-reperfusion (IR) injury in a rat. Male Sprague–Dawley rats were divided into three experimental groups: (1) sham rats underwent laparotomy, (2) IR-rats underwent occlusion of both superior mesenteric artery and portal vein for 30 min followed by 24 h of reperfusion, and (3) IR-LEP rats underwent IR and were treated with leptin given subcutaneously at a dose of 50 μg/kg once a day for 48 h before and 24 h following IR. Intestinal structural changes, enterocyte proliferation and enterocyte apoptosis were determined 24 h following IR. A non-parametric Kruskal–Wallis ANOVA test was used for statistical analysis with P < 0.05 considered statistically significant. Treatment with leptin resulted in a significant increase in bowel weight in ileum, mucosal weight in jejunum and ileum, mucosal DNA content in ileum, mucosal protein content in jejunum and ileum, villus height in jejunum and ileum, and crypt depth in jejunum compared to IR-animals. IR-LEP rats also had a significantly lower intestinal injury score as well as lower apoptotic index and higher cell proliferation index in jejunum and ileum compared to the IR-animals. In conclusion, pre-treatment with leptin prevents gut mucosal damage and improves intestinal rehabilitation following intestinal IR in a rat.     

Effect of nutritional rehabilitation on the development of intestinal brush border disaccharidases of postnatally malnourished weanling rats

The reversibility of the effects of postnatal malnutrition on the intestinal brush border enzymes and somatic and intestinal weights were examined using either ad libitum or restricted feedings. Malnutrition was induced in the immediate postnatal period by expanding newborn rat litters to 20 pups/dam. At 21 days of age, malnourished pups exhibited significantly decreased body and intestinal weights as compared to those from control litters. Malnourished pups also had significantly elevated lactase specific activities whereas sucrase and maltase activities were not affected in the proximal small intestine. With subsequent nutritional rehabilitation by an ad libitum (food available 24 h/day) or restricted feeding regimen (food available 2 h/day), body and intestinal weights remained significantly depressed by 56 days in malnourished as compared to control animals. Rats on 2-h feedings consumed approximately 35% of the food consumed by their ad libitum-fed counterparts. Comparison of the ratio of weight gained to the amount of food consumed did not demonstrate a greater food efficiency with any particular feeding pattern. With ad libitum or restricted feedings, lactase specific activity in the proximal segment attained control values by 14 days. Restricted feedings resulted in an apparent elevation of specific activity of sucrase and of maltase, when rats were sacrificed at one chosen time point. Multiple time studies in a 24-h cycle showed that maximal elevations in enzyme activities were associated with feeding time. There were no significant differences in mean specific daily enzyme activities between the two feeding regimens. Restricted feedings show no advantage in enzyme efficiency or in promoting the rate of recovery of the intestine after postnatal malnutrition.     

Longitudinal distribution of brush border hydrolases and morphological maturation in the intestine of the preterm infant

The morphological maturation and the distribution of brush border hydrolase activities were studied in the small intestine and the colon in newborn babies of 28-38 weeks gestational age. Lactase and sucrase activities were higher at term with maximal activity in the proximal intestine. In contrast, aminopeptidase and glucoamylase exhibited maximum activity in the distal part of the small bowel. Glucoamylase activity was already significant in the small intestine and in the colon of the preterm newborn. Sucrase activity present in the proximal colon of the preterm dropped to a negligible amount at term, whereas aminopeptidase activity increased, reaching values found in the small intestine. The enzymic changes occurring in the intestinal tract were related to the morphological maturation of the mucosa from fetal to adult type during late gestation. Accelerated morphological and functional maturation was observed in one preterm infant nourished intravenously for 12 days, these processes being independent of the presence of nutrients in the intestine. At term, the distal part of the intestine seems to have increased digestive capacities for peptides and polysaccharides. We present evidence that full-term, and to a lesser extent preterm infants are able to hydrolyse glucose polymers.     

Glucoamylase and disaccharidase activities in normal subjects and in patients with mucosal injury of the small intestine

The development of glucoamylase activity was compared to that of disaccharidase in the small intestinal mucosa of infants and children. By the age of one month, infants have glucoamylase and disaccharidase levels comparable to those of young adults, indicating that young infants may be able to digest and absorb starches. In infants and children with varying degrees of mucosal injury of the small intestine, the activities of glucoamylase decreased progressively with increasing severity of the villus atrophy. However, the reduction of lactase, palatinase, and sucrase activities was more severe than the loss of activities of glucoamylase and maltase. Thus, children and infants may tolerate polymers of glucose better than disaccharides when they have mucosal injury associated with prolonged diarrhea.     

Mosaic expression of brush-border enzymes in infants with chronic diarrhea and malnutrition.

The chronic diarrhea observed in young malnourished infants that is sensitive to dietary glucose and other carbohydrates is associated with variable degrees of patchy mucosal villous atrophy. To explore intrinsic mucosal function in the pathogenesis of this alimentary intolerance, we have conducted an immunohistologic investigation of brush-border enzyme proteins of clinically obtained, mucosal biopsy samples. We used a group of monoclonal antibodies against human brush-border aminopeptidase, sucrase/isomaltase (SI), maltase, and lactase enzyme proteins. SI was strongly and uniformly expressed in crypts and villi of 11 of the 14 subjects; in 3 subjects, however, SI was expressed in a mosaic pattern. Maltase and lactase were occasionally absent, but more commonly were expressed in a mosaic distribution. The mosaic expression of brush-border enzyme proteins has been reported in congenital enzyme deficiencies associated with normal intestinal histology. We report the mosaic expression of brush-border enzyme proteins as a functional alteration associated with a pathological lesion of the mucosa in infants with chronic diarrhea. Our observation challenges the existing concept of ontogenic regulation of brush-border enzyme activity.