Small intestinal length: a factor essential for gut adaptation

Epithelial growth of the small intestine in human infants

BACKGROUND

Findings in studies in rodents have suggested that epithelial growth of the small intestine is dependent on activation of the immune system. The purpose of this study was to compare changes of postnatal epithelial growth with immunologic activity in humans.

METHODS

Duodenal biopsies were obtained by endoscopy from 74 infants. Villus area, crypt length, and mitotic count were measured, using a microdissection technique. Enterocyte height, intraepithelial lymphocytes and mucosal mast cells were recorded in histologic sections, and soluble interleukin-2 receptor levels were measured in sera. These data were compared with those from 77 adult control subjects.

RESULTS

Mean +/- SD villus area was similar in infants compared with that in adults (0.364 +/- 0.108 mm2 vs. 0.339 +/- 0.1 mm2); but mean crypt length was 31% longer (270 +/- 56 microm vs. 206 +/- 29 microm; p < 0.0001), and mitotic count was 68% higher (4.2 +/- 2.8 vs. 2.5 +/- 1 per crypt; p < 0.0001) in infants. Enterocyte height was lower during infancy (27.0 +/- 3.4 microm vs. 30.9 +/- 4.6 microm; p < 0.0001). There was no evidence of a trophic effect on the small intestine of breast feeding compared with the effect of bottle feeding. Counts of intraepithelial lymphocytes but not mucosal mast cells were significantly less in infants. Mean soluble interleukin-2 receptor levels peaked during early infancy, compared with levels in adults (1,820 +/- 596 U/ml vs. 695 +/- 359 U/ml).

CONCLUSION

These results indicate that epithelial proliferation is increased during infancy at an age when immunologic activity is high.

Human milk IgA concentrations during the first year of lactation

AIMS

To measure the concentrations of total IgA in the milk secreted by both breasts, throughout the first year of lactation, in a cohort of Gambian mothers of infants at high risk of infection.

SUBJECTS AND METHODS

Sixty five women and their infants were studied monthly from the 4th to 52nd postpartum week. Samples of milk were obtained from each breast by manual expression immediately before the infant was suckled. Milk intakes were measured by test weighing the infants before and after feeds over 12 hour periods; IgA concentrations were determined by enzyme linked immunosorbent assay.

RESULTS

A total of 1590 milk samples was measured. The median (interquartile range) concentration of IgA for all samples was 0.708 (0.422-1.105) g/l; that in milk obtained from the left breast was 0.785 (0.458-1.247) g/l, and that in milk obtained from the right breast was 0.645 (0.388-1.011) g/l (p < 0.0001). There was no significant change in milk or IgA intakes with advancing infant age, but there was a close concordance of IgA concentrations between the two breasts, with "tracking" of the output of the left and right breasts. There was a significant (p < 0.01) negative correlation between maternal age and parity, and weight of milk ingested by infants. During the dry season (December to May) the median (interquartile range) IgA concentration was significantly higher at 0.853 (0.571-1.254) g/l than during the rainy season (June to November), when it was 0.518 (0.311-0.909) g/l (p < 0.0001).

CONCLUSIONS

Sustained IgA secretion is likely to protect suckling infants from microbial infection.

Jejunal glucose uptake and oxygen consumption in turkey poults selected for rapid growth

Two lines of turkey poults, one selected for rapid growth at 16 wk of age (F line) and the other a randombred control line (RBC2) were used to investigate the effect of selection for rapid growth on jejunal O2 consumption and glucose transport as well as whole-body O2 consumption. All trials used unsexed poults and were designed as a randomized complete block with day and line as independent variables. In Trial 1, 120 turkey poults, fed a standard starter ration (25.5% CP), were used to examine the effect of selection on feed intake, body weight gain, and efficiency from hatching (Day 0) to 13 d of age. At Day 14, 36 of 60 birds from each line were killed to measure intestinal length and weight and jejunal O2 consumption after 18 h of feed deprivation. Compared with the RBC2 line, the F line had relatively shorter but heavier small intestinal segments when adjusted by 18 h feed-deprived body weight (FBW; P < 0.001). The F line consumed more O2 over the entire jejunum adjusted to FBW than RBC2 line (43.8 vs 34.6 nmol O2/min.g FBW; P < 0.001). Jejunal ouabain- and cycloheximide-sensitive O2 consumption were greater (P < 0.05) in the F line. In Trial 2, 16 14-d-old poults from each line were used to measure in vitro jejunal glucose transport rate. There was no difference in glucose transport of the jejunum (nanomoles per minute per gram of FBW) between the lines. In Trial 3, 20 poults from each line were used to measure whole-body O2 consumption at 7 to 10 d of age. The F and RBC2 lines had similar whole-body O2 consumption rate per gram of FBW. These data suggest that selection of turkeys for rapid growth at 16 wk of age did not increase efficiency of jejunal glucose uptake in 14-d-old turkey poults.

Restriction of nutrition in utero selectively inhibits gastrointestinal growth in fetal sheep

This study examined the effects of reduced nutrition on fetal growth over the first half of gestation. Reduced nutrition was achieved by a combination of reduced maternal food intake and carunclectomy, a procedure which restricts the development of the placenta. There were no major effects of restriction on fetal body, tissue or organ growth, except for the gastrointestinal tract (GIT). Total GIT weight was lower in restricted fetuses than in controls. More specifically, it was growth of the small and large intestine which was compromised. Small intestinal weight was significantly lower, both in absolute terms and relative to body weight. The intestinal diameter and mucosal area were significantly lower in both small and large intestine of restricted fetuses. Maturation of enterocytes was also delayed in nutrient-restricted fetuses. In addition, there were focal lesions of the brush border present, indicating abnormal epithelial differentiation. By term, in growth-retarded fetuses, growth deficits in many organs were present, including the GIT. The present study suggests that GIT growth deficits may have a long-term etiology, including at their onset, abnormal cellular differentiation. These results could explain why GIT function in intrauterine growth-retarded infants is more likely to be compromised than in premature or term infants.

Determinants of lactose digestion in the miniature pig

Although lactose is an important nutrient in the diet of the infant and child, the factors contributing to its digestion have not been clarified adequately. We sought to determine the degree to which lactase activity and small intestinal transit explain lactose digestion, the average error (SEE) in estimating lactose digestion using these parameters, and the effect of age. We compared lactose digestion from both a 7% lactose-containing formula and a solution by determining lactose in ileostomy output in pig littermates at 10 days, 4 weeks, and 10 weeks of age. The entire small intestinal mucosa was assayed for lactase specific activity (micromol x min-1 x g protein-1), total activity (micromol x min-1), and whole-villus lactase activity. Transit time (min), and transit rate (cm/min) were measured. Meal type did not affect lactose digestion. Lactose digestion was explained best by lactase specific activity (formula, R2 = 0.73, SEE = 1.1; solution, R2 = 0.69, SEE = 1.0; P < 0.001). The next best parameter was total transit rate (formula, R2 = 0.69, SEE = 2.0; solution, R2 = 0.46, SEE = 1.3). The relationship with lactase specific activity was age related and there appeared to be a critical value of lactase specific activity above which essentially all the lactose was digested.

Dietary supplementation and rapid catch-up growth after acute diarrhoea in childhood

Diarrhoea is a major cause of short-term growth faltering in children of the developing world. If catch-up weight gain is delayed by inadequate dietary intake, or by further bouts of diarrhoea, progressive growth failure occurs. To test the hypothesis that early refeeding is as effective as later feeding after acute diarrhoea with weight loss, we measured the effects of a timed dietary intervention on weight gain after acute diarrhoea in underweight Gambian children. Thirty-four children aged 4-22 months with weight loss following acute diarrhoea were given a high-energy-protein supplement for 14 d beginning either immediately after rehydration or a fortnight later. With a 50% increase in energy intake and a 100% increase in protein intake there was a rapid and highly significant (P < 0.001) gain in weight within a fortnight whether the supplement was given immediately or 2 weeks after presentation. Rates of weight increase were similar whether supplementation was provided early or late, but over the full 28 d (of intervention and non-intervention) children who received late supplementation had greater overall weight gain (P < 0.02) than those supplemented early. Vigorous and early feeding with a high-energy-protein supplement should be central to the management of malnourished children with acute diarrhoea in developing countries, and may be as important as control of diarrhoea in preventing malnutrition and growth failure. This may be achieved in the community using locally available foods, in the face of continuing diarrhoea.

The interactive role of mucosal T lymphocytes in intestinal growth, development and enteropathy

Over the past 15-20 years, research has progressively focused on the mucosal T cell as the central factor in the initiation of physiological or pathological changes, first in the growth and maturation of the early (postnatal) intestine, and second in adult-type enteropathies resulting from sensitivity to either food or pathogen-derived antigens. T cell-mediated events may be measured, for example, in terms of specific immunopathologic patterns of change and injury, such as type 1 (lymphocyte infiltration), type 2 (crypt hyperplasia) and type 3 (flat-destructive), which can be recognized and quantitated microscopically; by determination of lymphocyte reactivity through secretion of interleukin-2 receptors (IL-2R) into plasma or expression by mucosal lymphocytes; by quantitation of lymphocyte subsets emigrating into inflamed tissues by immunoperoxidase-labelled monoclonal antibodies; or by the determination of T cell receptor polymorphisms. Alterations in intestinal growth, structure and function at weaning are likely to be T cell-mediated as they are analogous to the same type 1/2 lesions that reflect modulation of adult mucosal architecture in food and parasite-induced hypersensitivity reactions. Enteropathies associated with HIV infection and T cell deficiency display a milder degree of villous flattening and impaired crypt hyperplasia than that typical of gluten-sensitivity, suggesting a reversion to lesser degrees of mucosal pathology (type 1/2). Clearly more information will accrue; meanwhile the remarks in this brief survey should provide a firm basis whereby clinician and scientist can meet, and together recognize and further dissect the modulatory effect of T lymphocytes on mucosal structure and function.