Adaptation of the duodenum and ileum of the rat to mid-gut resection: enzyme activity and trace metal status

Intestinal adaptation after extensive small bowel resection: differential changes in growth and insulin-like growth factor system messenger ribonucleic acids in jejunum and ileum

The distal small bowel exhibits greater adaptive growth than proximal segments after partial small intestine resection. To explore this process, we evaluated adaptive cellularity, intestinal insulin-like growth factor (IGF) system messenger RNA (mRNA) transcripts, and effects of recombinant IGF-I treatment in jejunum and ileum of adult rats. Gastrostomy-fed animals underwent 80% jejuno-ileal resection or intestinal transection and reanastomosis without resection, followed by infusion of human recombinant IGF-I (2.4 mg/kgXday) or vehicle. After 7 days, resected rats demonstrated modest adaptive growth in jejunum and marked cell proliferation in ileum. Resection increased IGF-I mRNA in both jejunum (183%) and ileum (249%) and up-regulated IGFBP-4 mRNA levels in both tissues. IGFBP-3 mRNA fell significantly in ileum after resection. IGF-I infusion modestly increased ileal cellularity after resection, but had no effect in jejunum. IGF-I markedly increased IGFBP-3 mRNA levels in jejunum after both transection and resection. These data confirm that bowel resection induces greater adaptive growth in ileum than jejunum. IGF-I administration modestly increases ileal, but not jejunal, growth after resection. Increased levels of intestinal IGF-I and IGFBP-4 mRNA suggest roles for IGF-I and IGFBP-4 in mediating small bowel adaptation. Higher levels of jejunal IGFBP-3 mRNA may be related to limited jejunal vs. ileal growth after extensive jejuno-ileal resection.

Altered polyamine biosynthesis with aging after massive proximal small bowel resection in rat

We examined the effect of aging on polyamine biosynthesis in the small intestine. Two groups of male Wistar rats (young; 10-week-old, n = 40; old; 24-month-old, n = 40) underwent either a jejunal transection and reanastomosis or 90% proximal small bowel resection. The rats were sacrificed on the 1st, 2nd, 4th, and 7th postoperative day (POD). The mucosa was submitted for histological examination, weighed, and assayed for protein, DNA, RNA, and polyamine content. Ornithine decarboxylase (ODC) activity was measured and ODC mRNA in the mucosa was determined by Northern blot analysis. Compared with the values for wet weight and protein content in old rats, young rats showed significantly higher values for wet weight on the 1st and 2nd POD, and for protein content on the 1st POD, but there were no differences between young and old rats after the 4th POD. The values for ODC activity and ODC mRNA were significantly lower in old rats than in young rats on the 1st POD, but there were no differences between young and old rats after the 2nd POD. The value for putrescine in old rats was significantly lower on the 2nd POD, but was significantly higher on the 4th POD than that in young rats. The present study showed that, in old rats, the residual intestine after small bowel resection preserved sufficient adaptive capacity, but that the adaptive response was decreased. The findings in this study also suggest that a decrease in ODC mRNA expression is involved in the decreased adaptive response that occurs with aging.

Effects of intestinal resection, cholecalciferol and ascorbic acid on iron metabolism in rats

The effect of dietary supplementation with ascorbic acid or cholecalciferol on Fe utilization was studied using the metabolic balance technique, in rats in which 50% of the distal small intestine was removed, or in which the mid small intestine was transected and reanastomosed (controls). Three different diets were used. The first (basal diet) contained (g/kg dry wt): protein (casein + 50 mg D,L-methionine/g) 120 and fat (medium-chain triacylglycerols, olive oil and sunflower oil, in equal parts) 40. The other diets were obtained by adding ascorbic acid (150 mg/kg diet) or cholecalciferol (0.4 mg/kg diet) to the basal diet. Apparent digestibility coefficient (ADC) and Fe retention were significantly lower in resected animals than in their respective control groups (transected rats). However, the addition of ascorbic acid or cholecalciferol to the basal diet increased the ADC and Fe retention in both transected and resected rats. Five weeks after surgery, resection also resulted in a reduced concentration of Fe in the sternum, but did not reduce the concentration of haemoglobin or serum Fe total Fe-binding capacity or the concentration of Fe in liver, testes, femur or muscle (longissimus dorsi). Supplementation with ascorbic acid increased serum Fe concentration, while the concentration of Fe in muscle was reduced by supplementation with both ascorbic acid and cholecalciferol. Neither supplementation had any effect on the Fe concentration in other tissues, on haemoglobin concentration or plasma total Fe-binding capacity. Thus, supplementation with ascorbic acid or with cholecalciferol increased Fe absorption and reduced the concentration of Fe in muscle.

Structural and functional adaptation following jejunal resection in rabbits: effect of epidermal growth factor

BACKGROUND/AIMS

Remnant small intestine undergoes adaptation following massive resection. The aim of this study was to examine the effect of epidermal growth factor (EGF) on ileal adaptation following proximal resection.

METHODS

New Zealand white rabbits, aged 8 weeks, underwent 2/3 proximal resection, and ileal mucosal adaptation was assessed 10 and 21 days postsurgery. In a second series of experiments, animals with resection received oral EGF (40 micrograms.kg-1.day-1) for 5 days, and the effect on adaptation was assessed 10 days postsurgery.

RESULTS

Transection alone stimulated mucosal hyperplasia, intestinal sucrase specific activity, and glucose transport at 10 days but not at 21 days. Resection resulted in mucosal hyperplasia at both time periods and increased disaccharidase specific activity at 10 days postresection. In contrast, 3 O-methyl-D-glucose transport was significantly decreased compared with both groups at both time periods. EGF treatment in animals with resection did not alter mucosal proliferation but did stimulate maltase specific activity and caused a 3-4-fold increase in glucose transport and phlorizin binding.

CONCLUSIONS

Following proximal resection, adaptation of intestinal digestive and absorptive function does not parallel mucosal hyperplasia. Administration of EGF to resected animals enhances glucose absorption and may have a therapeutic role in the management of short gut syndrome.

Age-related changes in duodenal adaptation after distal small bowel resection in rat

Two groups of male Fisher 344 rats (young: 4 months old; aged: 25 months old) underwent either 70% distal small bowel resection or sham operation (small bowel transection). Rats from each treatment group of each age were sacrificed on the 10th (N = 15: young rats; N = 13: aged rats) or 20th (N = 15: young; N = 13: aged) postoperative day (POD), and the duodenal mucosa was weighed and assayed for DNA, RNA, and protein contents, as well as for specific activities of the disaccharidase, sucrase, maltase, and lactase. Compared to the sham operation, distal small bowel resection significantly increased DNA by 48%, RNA by 122%, and protein by 75% in young rats and DNA by 40%, RNA by 92%, and protein by 71% in aged rats on the 20th POD. Both young and aged rats showed similar adaptive hyperplasia on the 10th POD. On the 20th POD after distal small bowel resection, specific activities of all tested enzymes were significantly increased in young rats (sucrase +86%, maltase +110% and lactase +64%), but showed no significant changes in aged rats. These findings suggest that the duodenum of aged rats may have sufficient proliferative potential to respond to distal small bowel resection, but that the mechanisms governing return of function in response to distal small bowel resection are inhibited in aged rats, compared to those mechanisms in the young.

Differentiation status of rat enterocytes after intestinal adaptation to jejunoileal bypass

The differentiation status of epithelial cells in intestinal adaptation remains unclear. To determine whether enterocytes reach optimum maturity following adaptation after 85% shortening of the rat gut by jejunoileal bypass surgery, activities of two brush border enzymatic markers of differentiation, alkaline phosphatase and sucrase, were examined in subpopulations of epithelial cells isolated sequentially from the villus/crypt axis of normal (sham operated) and hyperplastic mucosa. In jejunal villi, adaptational hyperplasia was associated with an increase in total epithelial alkaline phosphatase, but not total sucrase, activity; alkaline phosphatase activity increased most obviously in cells at the 11-50% position (from the tip) on villi. In hyperplastic ileal villi, total alkaline phosphatase activity fell, although sucrase activity did not change significantly. Specific activity (per mg protein) of sucrase on jejunal villus epithelium was reduced by the adaptational changes to bypass; alkaline phosphatase specific activity remained unchanged. In the ileum, despite adaptational changes to bypass, there was no increase in the normally low specific activities of sucrase and alkaline phosphatase. Bypass surgery did not change the major site of expression of either enzyme on jejunal or ileal villi. In conclusion, enzymatic markers of functional differentiation are not all equally affected by adaptational hyperplasia. Hypertrophy of villi and increased cell proliferation seen in jejunum remaining exposed to luminal contents resulted in an increase in the alkaline phosphatase but not the sucrase content. This is not, therefore, the result of a simple immaturity of villus cells. Morphological adaptation in the ileum, however, is not accompanied by adaptation of brush border enzyme markers of differentiation, confirming a functional immaturity of these cells. Strategies for increasing the expression of these markers may have clinical value.