The surface area of the intestinal mucosa in the lactating rat

Environmental enteric dysfunction: gut and microbiota adaptation in pregnancy and infancy

Environmental enteric dysfunction (EED) is a subclinical syndrome of intestinal inflammation, malabsorption and barrier disruption that is highly prevalent in low- and middle-income countries in which poverty, food insecurity and frequent exposure to enteric pathogens impair growth, immunity and neurodevelopment in children. In this Review, we discuss advances in our understanding of EED, intestinal adaptation and the gut microbiome over the 'first 1,000 days' of life, spanning pregnancy and early childhood. Data on maternal EED are emerging, and they mirror earlier findings of increased risks for preterm birth and fetal growth restriction in mothers with either active inflammatory bowel disease or coeliac disease. The intense metabolic demands of pregnancy and lactation drive gut adaptation, including dramatic changes in the composition, function and mother-to-child transmission of the gut microbiota. We urgently need to elucidate the mechanisms by which EED undermines these critical processes so that we can improve global strategies to prevent and reverse intergenerational cycles of undernutrition.

Compensatory changes in villus morphology of lactating Mus musculus in response to insufficient dietary protein

Energetic challenges match intestinal size to dietary intake but less is known about how the intestine responds to specific macronutrient challenges. We examined how intestinal size responds to insufficient dietary protein at the microscopic level. Villi, enterocytes and surface area were measured across the length of the small intestine in non-reproductive and lactating Mus musculus fed isocaloric control or protein-deficient diets. Lactating mice on the protein-deficient diet exhibited a 24% increase in villus height and a 30% increase in enterocyte width in the proximal small intestine and an overall similar increase in surface area; on the control diet, changes in villus height were localized in the mid region. Flexibility localized to the proximal small intestine suggests that enterokinase, a localized enzyme, may be a candidate enzyme that promotes compensation for a protein-deficient diet. Such flexibility could allow species to persist in the face of anthropogenically induced changing dietary profiles.

Gastrointestinal capacity, gut hormones and appetite change during rat pregnancy and lactation

Pregnancy and lactation increase maternal appetite and adiposity, which in humans can lead to long-term body mass retention. Previous rat reproduction studies suggest that appetite-inhibiting gut hormone, peptide-YY (PYY), is elevated, despite hyperphagia also that gastrointestinal size increases. The present study characterised changes in orexigenic (appetite-stimulating) ghrelin and anorexigenic (appetite-inhibiting) PYY and glucagon-like peptide-1 (GLP-1), and gastrointestinal architecture during pregnancy and lactation, in matched fed and fasted plasma and gut tissue samples taken during the dark phase. Enteroendocrine cells were immunolabelled, and gut masses and lengths were measured. Fasted plasma ghrelin reduced during pregnancy: it was lowest by day 18, recovered to control values at parturition, then increased by the end of lactation. Ghrelin-immunoreactive stomach cells and stomach ghrelin concentrations were highest at birth, prior to the onset of lactation-associated hyperphagia. Plasma fed GLP-1 concentrations were elevated during pregnancy, and together with higher colon concentrations of PYY and GLP-1 during early lactation, they were associated with gastrointestinal tissue expansion, not satiety. Body mass increased during lactation, whereas white adipose tissue depots depleted. Extensive gut remodelling coincided with elevated colon concentrations of PYY and GLP-1. Modifications included stomach and caecum expansion, and duodenal, ascending and descending colon circumference increases, all peaking by day 10 of lactation; increased intestinal masses and lengths peaking at lactation day 10 for small intestine and lactation day 25 for large intestine. If these physical tissue increases persist post-partum, they could accelerate future nutrient assimilation and storage in dams, and may contribute to increased obesity risk.

Cellular metabolic rates and oxidative stress profiles in primary fibroblast cells isolated from virgin females, reproductively experienced females, and male Sprague-Dawley rats

Life-history theory posits that differences in reproductive strategies may dictate lifespans of organisms. Animals that have higher investments in reproduction in terms of litter size and frequency of litters tend to have shorter lifespans. The accumulation of oxidative stress damage has been proposed to be a cost of reproduction and a mediator of life-histories among animals, however, the implications of reproduction on oxidative stress still remain unclear. We tested physiological consequences of reproduction on metabolism and oxidative stress of Sprague-Dawley Rats (Rattus norvegicus) with various reproductive experiences at the cell level. We grew primary dermal fibroblasts from Sprague-Dawley rats which have the potential of having large litters frequently. Cells were isolated from virgin females, primiparous females, multiparous females, and reproductively-experienced males. We measured basal oxygen consumption (OCR), proton leak, ATP production, spare respiratory capacity, coupling efficiency and glycolysis using a Seahorse XF96 oxygen flux analyzer. Additionally, we measured rates of RS (reactive species) production, reduced glutathione (GSH), mitochondrial content, and lipid peroxidation (LPO) damage to quantify oxidative stress. There were no significant differences in any OCR or glycolytic parameters across any of our groups. However, reproductively-experienced females had significantly lower rates of LPO damage as compared with virgin females and males, as well as nonsignificant decreases in GSH concentration. Decreases in LPO damage and GSH indicate that reproductively-experienced females potentially use their endogenous antioxidant system to combat delirious effects of increased metabolism during reproduction. Our results suggest that reproduction may, in fact, have a protective effect in females.

Mood, Food, and Fertility: Adaptations of the Maternal Brain

Successfully rearing young places multiple demands on the mammalian female. These are met by a wide array of alterations in maternal physiology and behavior that are coordinated with the needs of the developing young, and include adaptations in neuroendocrine systems not directly involved in maternal behavior or lactation. In this article, attenuations in the behavioral and neuroendocrine responses to stressors, the alterations in metabolic pathways facilitating both increased food intake and conservation of energy, and the changes in fertility that occur postpartum are described. The mechanisms underlying these processes as well as the factors that contribute to them and the relative contributions of these stimuli at different times postpartum are also reviewed. The induction and maintenance of the adaptations observed in the postpartum maternal brain are dependent on mother-young interaction and, in most cases, on suckling stimulation and its consequences for the hormonal profile of the mother. The peptide hormone prolactin acting on receptors within the brain makes a major contribution to changes in metabolic pathways, suppression of fertility and the attenuation of the neuroendocrine response to stress during lactation. Oxytocin is also released, both into the circulation and in some hypothalamic nuclei, in response to suckling stimulation and this hormone has been implicated in the decrease in anxiety behavior seen in the early postpartum period. The relative importance of these hormones changes across lactation and it is becoming increasingly clear that many of the adaptations to motherhood reviewed here reflect the outcome of multiple influences. © 2016 American Physiological Society. Compr Physiol 6:1493-1518, 2016.

Nutrient availability, the microbiome, and intestinal transport during pregnancy

Adequate adaptation of the gastrointestinal tract is important during pregnancy to ensure that the increased metabolic demands by the developing fetus are met. These include changes in surface area mediated by villus hypertrophy and enhanced functional capacity of individual nutrient receptors, including those transporting glucose, fructose, leucine, and calcium. These processes are regulated either by the enhanced nutrient demand or are facilitated by changes in the secretion of pregnancy hormones. Our review also covers recent research into the microbiome, and how pregnancy could lead to microbial adaptations, which are beneficial to the mother, yet are also similar to those seen in the metabolic syndrome. The potential role of diet in modulating the microbiome during pregnancy, as well as the potential for the intestinal microbiota to induce pregnancy complications, are examined. Gaps in the current literature are highlighted, including those where only historical evidence is available, and we suggest areas that should be a priority for further research. In summary, although a significant degree of adaptation has been described, there are both well-established processes and more recent discoveries, such as changes within the maternal microbiome, that pose new questions as to how the gastrointestinal tract effectively adapts to pregnancy, especially in conjunction with maternal obesity.

Histomorphometric changes of small intestine in pregnant rat

Food intake of rats increases during pregnancy. This requires changes in the structure of the small intestine to absorb additional food. The aim of the present study was to investigate the morphological changes in the layers of small intestine in rats during pregnancy. Duodenum, jejunum and ileum of 18 pregnant Sprague-Dawley rats (day 7, 14 and 21 of pregnancy) were collected. Villous height and width and thickness of lamina propria, tunica muscularis entirely and separately (circular and longitudinal layers) were measured on transverse sections. During pregnancy increasing villi length and muscular layer thickness was observed in duodenum. Furthermore, along with the progress of gestation greatest histomorphometric change in small intestine was observed in the jejunum. The reduction in the ileum histomorphologic indices was observed during pregnancy. In conclusion, increase in histomorphologic indices of duodenum and jejunum supplies more capacity of duodenum to digest food intake during pregnancy and decrease in these indices in ileum controls the absorption of excess produced amino acids and glucose by hyperphagia.

Repeated exposure to severely limited sleep results in distinctive and persistent physiological imbalances in rats

Chronic sleep disruption in laboratory rats leads to increased energy expenditure, connective tissue abnormalities, and increased weights of major organs relative to body weight. Here we report on expanded findings and the extent to which abnormalities become long-lasting, potentially permanent changes to health status after apparent recuperation from chronic sleep disruption. Rats were exposed 6 times to long periods of disrupted sleep or control conditions during 10 weeks to produce adaptations and then were permitted nearly 4 months of undisturbed sleep. Measurements were made in tissues from these groups and in preserved tissue from the experimental and control groups of an antecedent study that lacked a lengthy recuperation period. Cycles of sleep restriction resulted in energy deficiency marked by a progressive course of hyperphagia and major (15%) weight loss. Analyses of tissue composition in chronically sleep-restricted rats indicated that protein and lipid amounts in internal organs were largely spared, while adipose tissue depots appeared depleted. This suggests high metabolic demands may have preserved the size of the vital organs relative to expectations of severe energy deficiency alone. Low plasma corticosterone and leptin concentrations appear to reflect low substrate availability and diminished adiposity. After nearly 4 months of recuperation, sleep-restricted rats were consuming 20% more food and 35% more water than did comparison control rats, despite normalized weight, normalized adipocytes, and elevated plasma leptin concentrations. Plasma cholesterol levels in recuperated sleep-restricted rats were diminished relative to those of controls. The chronically increased intake of nutriments and water, along with altered negative feedback regulation and substrate use, indicate that internal processes are modified long after a severe period of prolonged and insufficient sleep has ended.

Recurrent restriction of sleep and inadequate recuperation induce both adaptive changes and pathological outcomes

Chronic restriction of a basic biological need induces adaptations to help meet requisites for survival. The adaptations to chronic restriction of sleep are unknown. A single episode of 10 days of partial sleep loss in rats previously was shown to be tolerated and to result in increased food intake and loss of body weight as principal signs. The purpose of the present experiment was to investigate the extent to which adaptation to chronic sleep restriction would ameliorate short-term effects and result in a changed internal phenotype. Rats were studied during 10 wk of multiple periods of restricted and unrestricted sleep to allow adaptive changes to develop. Control rats received the same ambulatory requirements only consolidated into periods that lessened interruptions of their sleep. The results indicate a latent period of relatively stable food and water intake without weight gain, followed by a dynamic phase marked by enormous increases in food and water intake and progressive loss of body weight, without malabsorption of calories. Severe consequences ensued, marked especially by changes to the connective tissues, and became fatal for two individuals. The most striking changes to internal organs in sleep-restricted rats included lengthening of the small intestine, decreased size of adipocytes, and increased incidence of multilocular adipocytes. Major organs accounted for an increased proportion of total body mass. These changes to internal tissues appear adaptive in response to high energy production, decomposition of lipids, and increased need to absorb nutrients, but ultimately insufficient to compensate for inadequate sleep.

Changes in the body and its organs during lactation: nutritional implications

Lactation makes considerably greater demands on the mother's body than pregnancy does in species where the young are helpless at birth and depend on mother's milk for a comparatively long time. These species include many rodents and carnivores and also man. The requirements for the production of milk are met partly from within, by the mobilization of the mother's body tissues, and partly from without, by an increased food intake. Both ways lead to alterations in the composition of the mother's body which may or may not be permanent. Fat laid down in the body during pregnancy is used and there may also be losses of calcium from the skeleton, especially if the calcium intake is low. Whether extra protein is deposited during human pregnancy and lost again during lactation still remains an open question. In rats, the answer depends partly on the intake of protein and energy. The increase in food intake during lactation in some species is so great that the gastrointestinal tract grows considerably to deal with it. In the rat, the small intestine more than doubles its weight. The intestinal wall dilates and the area of mucosa almost doubles. The liver also increases considerably in size owing to an increase in both number and size of cells. After lactation, the liver becomes smaller again, and so does the amount of protein in it, but there is no loss of cells, so that rats that have reared litters have more cellular livers than those that have not. There is no indication whether similar changes occur in women.

The physiological costs of reproduction in small mammals

Life-history trade-offs between components of fitness arise because reproduction entails both gains and costs. Costs of reproduction can be divided into ecological and physiological costs. The latter have been rarely studied yet are probably a dominant component of the effect. A deeper understanding of life-history evolution will only come about once these physiological costs are better understood. Physiological costs may be direct or indirect. Direct costs include the energy and nutrient demands of the reproductive event, and the morphological changes that are necessary to facilitate achieving these demands. Indirect costs may be optional 'compensatory costs' whereby the animal chooses to reduce investment in some other aspect of its physiology to maximize the input of resource to reproduction. Such costs may be distinguished from consequential costs that are an inescapable consequence of the reproductive event. In small mammals, the direct costs of reproduction involve increased energy, protein and calcium demands during pregnancy, but most particularly during lactation. Organ remodelling is necessary to achieve the high demands of lactation and involves growth of the alimentary tract and associated organs such as the liver and pancreas. Compensatory indirect costs include reductions in thermogenesis, immune function and physical activity. Obligatory consequential costs include hyperthermia, bone loss, disruption of sleep patterns and oxidative stress. This is unlikely to be a complete list. Our knowledge of these physiological costs is currently at best described as rudimentary. For some, we do not even know whether they are compensatory or obligatory. For almost all of them, we have no idea of exact mechanisms or how these costs translate into fitness trade-offs.

Morphometric study of the guinea pig small intestine during development

The mucosal surface area of the guinea pig duodenum, jejunum, and ileum was determined during development, in three age groups: 1-day-old and 2- and 12-week-old animals. The morphometric analysis was performed at three magnification levels. The nominal surface area was determined at the macroscopic level, from intestinal length and perimeter. Villus and microvillus amplification factors were estimated at light-microscopic and transmission electron-microscopic levels, respectively. We found: (1) an increase in the nominal surface area that is maximal in the ileum (7.7-fold); (2) an increase in the villus amplification factor in the duodenum (1.4-fold) and a decline in the jejunum and ileum (0.8-fold), although in the jejunum villus dimensions rise; and (3) a similar increase in the microvillus amplification factor in the three segments (1.1- to 1.4-fold). In conclusion, the total mucosal surface area increased from day 1 to week 12, by 3-fold in the duodenum and jejunum and by 8-fold in the ileum. Regionally, the jejunum shows the largest mucosal surface area, followed by the ileum, and, finally, the duodenum.

Adaptation of the maternal intestine during lactation

One of the most dramatic adaptations to lactation is a large increase in the size and complexity of maternal intestine. Although there are few data on changes in intestinal size, intestinal enlargement has been observed in many taxonomic groups. In this review I describe the morphological and physiological changes in the intestinal mass of lactating animals and discuss their functional significance. The observed increases maintain the digestive efficiency of the food, as well as insure adequate absorption of nutrients in the face of the increased energy demand that accompanies lactation. The extent of the increase in size is proportional to the increase in energy demand. It is clear that if the intestine did not accommodate during lactation mothers would not have the capacity to absorb the nutrients need to maintain their energy demand.

Toxicokinetics of cadmium in lactating and nonlactating ewes after oral and intravenous administration

We studied the toxicokinetics of cadmium on two groups of ewes, a lactating group and a nonlactating group, after single intravenous and oral administrations of cadmium chloride using a semisimultaneous method and a three-compartment model. The nonlactating ewes showed a low cadmium bioavailability (0.12-0.22%), a large steady-state volume of distribution (23.8 +/- 5.4 liter/kg), and a low blood clearance (0.20 +/- 0.03 liter/kg/day). Their mean residence time was 113 +/- 28 days. The lactating ewes had a higher bioavailability (0.33-1.7%). Their mean residence time was close to that in nonlactating ewes despite a greater blood clearance (0.46 +/- 0.013 liter/kg/day) because the volume of distribution of cadmium in the body was larger (Vss = 48.8 +/- 10.3 liter/kg). Their cadmium clearance in milk, changing with time, remained low and could not explain their higher blood clearance. In one nonlactating ewe, a greater cadmium bioavailability (5%) increased cadmium in the body. Increased cadmium amounts could induce renal damage and shorten the mean residence time (78 days).

An investigation into the reversibility of the morphological and cytokinetic changes seen in the small intestine of riboflavin deficient rats

BACKGROUND

Impaired iron handling in riboflavin deficiency is thought to be partially a result of significant morphological and cytokinetic changes within the small intestine.

AIMS

The aim of the study was to find out if the responses of the rat small intestine to riboflavin deficiency induced at weaning could be reversed upon repletion.

SUBJECTS

48 female weanling Wistar rats were used for the purpose of the study.

METHODS

Rats were fed a riboflavin deficient diet or a complete control diet for a period of five weeks followed by a repletion period of up to three weeks. Rats were killed on day 0, 2, 7, or 21 of repletion. The duodenum was removed and fixed for subsequent analysis.

RESULTS

Five weeks of riboflavin deficiency significantly changed the morphology and cytokinetics of the duodenum; the changes were not reversed within the 21 day repletion period despite biochemical evidence for a correction of the deficiency.

CONCLUSIONS

The results show that the small intestine cannot readily recover from a period of riboflavin deficiency induced at weaning, supporting the notion that the weaning period is a critical time for gastrointestinal development and highlighting the importance of adequate nutrition during infancy.

Whole population cell kinetics of jejunal and colonic epithelium in lactating dams

Previous studies make it likely that the response of the intestinal epithelium as a whole to lactation is different from that observed in the crypt population alone. We confirm this difference by whole population cell kinetics measurements of jejunal and colonic epithelium in mice that have been suckling pups for various lengths of time. We found that the fraction of cells in S phase in jejunal epithelium was significantly increased after only 1 week of lactation, maintained this elevated level after 2 weeks of lactation, but returned to normal during the third week of lactation. The cell number density in jejunum was also significantly higher after 2 and 3 weeks of lactation before returning to normal by 4 weeks. In the colonic epithelium no changes were found in the distribution of cells in G1, S, and G2 + M phases. However, a significant increase in cell number density was observed after 2 weeks of lactation, followed by a sharp decrease to a level significantly below that of normal mice after 3 and 4 weeks of lactation. We conclude that the observed significant increase in the fraction of S phase in jejunal epithelium of lactating mice is probably due to a smaller relative expansion of the villus population when compared with the expansion of the crypt population. Our data also indicate that a number of cell kinetic parameters in the intestinal epithelium of lactating mice are changing throughout the period of lactation. Thus the intestinal epithelium is probably not in a steady state during lactation.

Striated brush border of intestinal absorptive epithelial cells: stereological studies on microvillous morphology in different adaptive states

Different regions of small bowel were examined in five groups of rats in three separate experiments. The effects on mucosal morphology of position along the bowel, induced hypoproliferation (due to fasting), and induced hyperproliferation (due to streptozotocin diabetes) were investigated. Intestines fixed by in situ perfusion with buffered glutaraldehyde were sampled by strictly randomised procedures. Pieces of tissue from segments of roughly equal length were processed for electron microscopy and embedded in resin. Complete transverse sections were cut for light microscopy and estimates of villous surface areas were obtained by stereological methods devised for the purpose. Ultrathin sections from random sectors of the same tissue blocks were sampled systematically to obtain micrographs of the villous surface. These were analysed for quantitative information about microvilli (length, diameter, surface area, and number). Structural quantities from individual segments were pooled to provide values for the entire small bowel. Significant regional differences in villous and microvillous dimensions were found in all groups. The numbers of microvilli per bowel were remarkably constant in all control groups. Other variables were estimated reproducibly in rats of the same sex, strain, and average body weight. Effective absorptive surfaces did not show a linear gradient but tended to peak in middle segments. Neither fasting nor induced diabetes altered the mean length, diameter, or packing density of microvilli. However, surfaces due to villi and microvilli altered commensurately during fasting and induced diabetes. Therefore cell number seems to be the key quantity for determining villous and microvillous surface areas. The findings are discussed in the context of kinetic, biochemical, and physiological changes found in different adaptive states.

Mechanisms of adaptation in rat small intestine: regional differences in quantitative morphology during normal growth and experimental hypertrophy

The gross and microscopical dimensions of small intestines from three groups of rats were investigated by morphometric (mainly stereological) methods. The groups were chosen to represent relatively 'steady state' situations: normal growth (over a 12 week period) and intestinal hyperplasia due to streptozotocin-diabetes of 12 weeks duration. Four intestinal segments were sampled along each intestine. For normal groups, no interaction effects were found, suggesting that growth affected all regions of the small intestine in the same way. Older rats were heavier and their intestines were longer and narrower. In addition, villous surface area was more extensive and the villi differed in shape. Volumes of crypts, submucosa and muscularis externa were all reduced. Diabetic animals weighed less than age-matched controls and their intestines were wider but not significantly longer. All surface areas and volumes were increased substantially. However, hypertrophy of the muscularis externa was not detected by measuring muscularis thickness. Villi altered their shape. At least for villous height, the effects of diabetes were greater in terminal segments. These findings are discussed in the context of the reported effects of age and experimental hyperplasia (including diabetes) on intestinal architecture and behaviour.

Crypts, villi and microvilli in the small intestine of the rat. A stereological study of their variability within and between animals

Small intestines from normal adult rats were quantified by optical and electron microscopy using stereological principles devised for the purpose. Five segments per bowel were examined. Baseline data characterising villi, microvilli and crypts of Lieberkühn were used to study differences between segments and between animals. Intestines fixed by in situ perfusion had, on average, 100 cm2 of primary mucosa. This basic surface was amplified to 500 cm2 by villi and to 1 m2 by the microvilli of enterocytes. Villous and microvillous surface areas may scale to body weight in the same way as metabolic requirements. Proximodistal gradients in mucosal architecture existed for the volumes and surface areas of villi and for the numbers, lengths, diameters and surface areas of microvilli. Most variables were higher proximally and declined towards the terminal ileum. The volume of crypts stayed constant throughout the entire intestine and ratios between villous dimensions (volumes and surface areas) and crypt volume did not vary between animals. Findings are discussed in the context of regional differences in bowel function and of their relevance to studies of epithelial kinetics.

Changes in the intestinal microvillous surface area during reproduction and ageing in the female rat

A morphometric study has been undertaken of the changes that occur in the microvillous surface area of young, pregnant, lactating, old and senescent rats. It has been shown that the microvilli are organelles with a quite stable conformation and that they exhibit no large scale dimensional changes throughout almost the entire life span. Lactation, however, does induce an apparent increase in microvillous surface area which may be associated with the significant changes which occur to the structure of the villus during reproduction in the rat.

Effect of dietary carbohydrate on monosaccharide uptake by mouse small intestine in vitro

Using intestinal sleeves in vitro, we studied the effect of dietary carbohydrate on active monosaccharide uptake in mice. Dietary carbohydrate did not affect numerous parameters of intestinal structure, such as length, circumference, weight, protein content, villus dimensions and density, and area at the villus level. Mice on a carbohydrate-free diet had active D-glucose uptake relatively independent of position along the small intestine. A carbohydrate-containing diet reversibly and within 1 day stimulated uptake except in the ileum, restoring the proximal-to-distal gradient in glucose uptake normally observed. This stimulation involved a 81-116% increase in the Michaelis- Menton constant Vmax, and also an apparent increase in the Michaelis- Menton constant Km, that may however be an artifact arising from unstirred-layer effects. Active uptake of 3-O-methyl-D-glucose also increased, permeability to glucose remained unchanged, and proline uptake reversibly decreased (probably due to the lower protein content of the carbohydrate-containing diets). The effect of fasting on active monosaccharide uptake seemed largely due to withdrawal of dietary carbohydrate, rather than of calories per se. It is concluded that dietary carbohydrate causes induction of monosaccharide carriers in the intestine, along with its more familiar induction of pancreatic amylase and intestinal disaccharidases. Substrate-dependent carrier induction may be physiologically significant in maintaining the proximal-to-distal gradient of glucose transport. An appendix presents measurements of villus area as a function of position along the intestine.

Bioavailability of orally administered cadmium and lead to the mother, fetus, and neonate during pregnancy and lactation: an overview

An overview of pathways for bioavailability of cadmium and lead from diet to mother to fetus during pregnancy and to neonate during lactation is presented. Increased uptake and retention of cadmium by the mother during pregnancy and lactation occurs, with sequestration of cadmium in the maternal kidney, liver, placenta and mammary tissue; the fraction of maternal body burden transferred to the young is small. In contrast, a substantial portion of the lead absorbed from the diet by the mother during pregnancy and lactation is transferred to the fetus via the placenta and to the neonate via the milk.

Lead metabolism in lactation

A 2-fold increase in lead absorption was observed in lactating animals which received 2 mg Pb/l in drinking water. About one-half of the absorbed lead was transferred to the litters.

The effect of pregnancy and lactation on the absorption of zinc and lysine by the rat duodenum in situ

1. The absorption of zinc by the duodenum of the rat was greatly enhanced at late stages of pregnancy and during lactation. 2. During pregnancy no increase in lysine uptake could be demonstrated, but during lactation, when further increases in Zn absorption occurred, uptake of lysine was increased. 3. The increased absorption of Zn at different stages of pregnancy and lactation appeared to be related to the demand made by the developing foetuses and post-natal offspring.

Changes in the mucosal surface area of the small gut of rats of different ages

Changes in the mucosal surface area of the small intestine of the ageing male Wistar rat were investigated. The results show that the mucosal surface area (Ma) and, even more, the mucosal area per unit serosal area (Ra) diminishes along the length of the small intestine (excluding the duodenum) in the young rat. In adults, however, there is relative constancy of these parameters along the small intestine. The serosal circumference (Sc) of the intestinal segments investigated increased considerably with advancing age.

Changes in intestinal cell kinetics in the small intestine of lactating mice

The enlargement of the small intestine of mice during lactation is due, at least in part, to hyperplasia in the mucosal crypts and villi. The number of cells per crypt increases by 130% and the cell production rate by 63% after 15 days of lactation. These parameters were measured from crypt squashes and sections using both double-label and PLM techniques. Neither the numbers of crypts and villi in the small intestine nor the turnover time of post-mitotic cells on the villi changed. A number of factors appear to act in concert during lactation to trigger this increase in epithelial cell number in the small intestine. The experiments reported suggest a role for the increased quantity of food consumed by the lactating animal, for changing hormonal levels, and for the increased demands placed on the body by milk production.

The effect of pregnancy and lactation on food intake, gastrointestinal anatomy and the absorptive capacity of the small intestine in the albino rat

1. Food consumption, live weight, anatomical measurements on the gut organs and the absorptive capacity of the small intestine for L-leucine and D(plus)-glucose were made on virgin (control), pregnant and lactating albino rats. 2. Food intake increased by approximately 60% during pregnancy and a further 250% during lactation. 3. Pregnancy did not markedly influence the gross anatomy of the gastrointestinal tract. There was evidence for increased villus height and percentage water in the small intestine and for increased length of the colon during pregnancy. 4. During lactation, the alimentary canal progressively increased in weight and size. It partially regressed following weaning. 5. All anatomical measurements, except the length of the small intestine, completely regressed to control values within 20 d of weaning. The increased intestinal length had not completely regressed by day 30 post-weaning. 6. No significant change was observed in absolute absorption of glucose or leucine during pregnancy. 7. Absolute absorption of leucine and of glucose was increased during lactation. Greatest absorption occurred on the 10th day of lactation. 8. Results for absorption of leucine and glucose per unit length indicated that the ability of the mucosal cells to absorb or the number of absorptive cells/mm had changed during lactation and the post-lactation periods.

Characterization of the kinetics of the passive and active transport mechanisms for bile acid absorption in the small intestine and colon of the rat

Bile acid uptake occurs via passive diffusion in all regions of the intestine and via active absorption in the ileum. Determination of the passive permeability coefficient for ionized monomers ((*)P(-)) demonstrated that permeability decreased by a factor of 3.4, 6.8, and 8.1 for the addition of a hydroxyl, glycine, or taurine group, respectively, to the steroid nucleus. Removal of the negative charge increased permeation by a factor of 4.4; however, permeability coefficients for the protonated monomers showed the same relative decrease with addition of a hydroxyl group. The calculated incremental free energies of solution (deltaDeltaF(W-->1)) associated with these additions equaled + 757 (hydroxyl), + 1178 (glycine), and + 1291 (taurine) cal/mole. Passive permeability coefficients for the transverse colon showed the same relative relationships among the various bile acids. After making appropriate corrections for passive permeability across the ileum, apparent values for the maximal transport velocity ((*)V(max)) and Michaelis constant ((*)K(m)) of the active transport system were measured. (*)V(max) depended upon the number of hydroxyl groups on the steroid nucleus; values for the trihydroxy bile acids were high (1543-1906 pmoles/min per cm) while those for the dihydroxy (114-512 pmoles/min per cm) and monohydroxy (45-57 pmoles/min per cm) acids were lower. In contrast, (*)K(m) values were related to whether the bile acid was conjugated; unconjugated bile acids had values ranging from 0.37 to 0.49 mM, while values for the conjugated bile acids were approximately half as high (0.12-0.23 mM).

Three-demensional structure of the rat small intestinal mucosa related to mucosal dynamics. II. Mucosal structure and dynamics in the lactating rat

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Three-dimensional structure of the rat small intestinal mucoas related to mucosal dynamics. 3. Mucosal structure and dynamics in the rat infested with the nematode Nippostrongylus brasiliensis

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