Regulation of growth and development of the gastrointestinal tract

Regulatory role of l-proline in fetal pig growth and intestinal epithelial cell proliferation

l-proline (Pro) is a precursor of ornithine, which is converted into polyamines via ornithine decarboxylase (ODC). Polyamines plays a key role in the proliferation of intestinal epithelial cells. The study investigated the effect of Pro on polyamine metabolism and cell proliferation on porcine enterocytes in vivo and in vitro. Twenty-four Huanjiang mini-pigs were randomly assigned into 1 of 3 groups and fed a basal diet that contained 0.77% alanine (Ala, iso-nitrogenous control), 1% Pro or 1% Pro + 0.0167% α-difluoromethylornithine (DFMO) from d 15 to 70 of gestation. The fetal body weight and number of fetuses per litter were determined, and the small and large intestines were obtained on d 70 ± 1.78 of gestation. The in vitro study was performed in intestinal porcine epithelial (IPEC-J2) cells cultured in Dulbecco's modified Eagle medium-high glucose (DMEM-H) containing 0 μmol/L Pro, 400 μmol/L Pro, or 400 μmol/L Pro + 10 mmol/L DFMO for 4 d. The results showed that maternal dietary supplementation with 1% Pro increased fetal weight; the protein and DNA concentrations of the fetal small intestine; and mRNA levels for potassium voltage-gated channel, shaker-related subfamily, member 1 (Kv1.1) in the fetal small and large intestines (P < 0.05). Supplementing Pro to either gilts or IPEC-J2 cells increased ODC protein abundances and polyamine concentrations in the fetal intestines and IPEC-J2 cells (P < 0.05). In comparison with the Pro group, the combined administration of Pro and DFMO reduced the expression of ODC protein and spermine concentration in the fetal intestine, as well as the concentrations of putrescine, spermidine and spermine in IPEC-J2 cells (P < 0.05). Meanwhile, the percentage of cells in the S-phase and the mRNA levels of proto-oncogenes c-fos and c-myc were increased in response to Pro supplementation, whereas depletion of cellular polyamines with DFMO increased tumor protein p53 (p53) mRNA levels (P < 0.05). Taken together, dietary supplementation with Pro improved fetal pig growth and intestinal epithelial cell proliferation via enhancing polyamine synthesis.

Developmental milestones in neonatal and juvenile C57Bl/6 mouse - Indications for the design of juvenile toxicity studies

There is a growing demand for wild type mice and mouse models of disease that may be more representative of human conditions but there is little information on neonatal and juvenile mouse anatomy. This project produces sound and comprehensive histology background data on the developing neonatal mouse at different time points from Day 0 until Day 28. The work describes optimal methods for tissue harvesting, fixation and processing from the neonatal and juvenile mice which can be used in routine toxicology studies. A review of the available literature revealed inconsistencies in the developmental milestones reported in the mouse. Although it is true that the sequence of events during the development is virtually the same in mice and rats, important developmental milestones in the mouse often happen earlier than in the rat, and these species should not be used interchangeably.

Short-Term Neonatal Oral Administration of Oleanolic Acid Protects against Fructose-Induced Oxidative Stress in the Skeletal Muscles of Suckling Rats

Nutritional manipulations in the neonatal period are associated with the development of negative or positive health outcomes later in life. Excessive fructose consumption has been attributed to the increase in the global prevalence of metabolic syndrome (MetS) and the development of oxidative stress. Oleanolic acid (OA) has anti-diabetic and anti-obesity effects. We investigated the protective potential of orally administering OA in the neonatal period, to prevent fructose-induced oxidative stress, adverse health outcomes and maturation of the gastrointestinal tract (GIT) in suckling rats. Seven-day old Sprague-Dawley rats (N = 30) were gavaged daily with 10 mL/kg of: distilled water (DW), oleanolic acid (OA; 60 mg/kg), high fructose solution (HF; 20% w/v), or OAHF for 7 days. On day 14, tissue samples were collected to determine clinical health profiles, hepatic lipid content, and activity of anti-oxidant enzymes. Furthermore, biomarkers of oxidative stress and anti-oxidant capacity in the skeletal muscles were assessed. The gastrointestinal tract (GIT) morphometry was measured. Rats in all groups grew over the 7-day treatment period. There were no significant differences in the terminal body masses, GIT morphometry, surrogate markers of general health, liver lipid content across all treatment groups (p < 0.05). Neonatal fructose administration decreased the activity of catalase, depleted GSH and increased lipid peroxidation. However, the level of GSH and catalase activity were improved by neonatal OA treatment. Short-term oral OA administration during the critical developmental period protects against fructose-induced oxidative stress without adverse effects on health outcomes associated with MetS or precocious development of the GIT in suckling male and female rats.

Points to Consider in Designing and Conducting Juvenile Toxicology Studies

In support of a clinical trial in the pediatric population, available nonclinical and clinical data provide input on the study design and safety monitoring considerations. When the existing data are lacking to support the safety of the planned pediatric clinical trial, a juvenile animal toxicity study is likely required. Usually a single relevant species, preferably a rodent, is chosen as the species of choice, while a nonrodent species can be appropriate when scientifically justified. Juvenile toxicology studies, in general, are complicated both conceptually and logistically. Development in young animals is a continuous process with different organs maturing at different rates and time. Structural and functional maturational differences have been shown to affect drug safety. Key points to consider in conducting a juvenile toxicology study include a comparative development of the organ systems, differences in the pharmacokinetics/absorption, distribution, metabolism, excretion (PK/ADME) profiles of the drug between young animal and child, and logistical requirement in the juvenile study design. The purpose of this publication is to note pertinent points to consider when designing and conducting juvenile toxicology studies and to aid in future modifications and enhancements of these studies to enable a superior predictability of safety of medicines in the pediatric population.

Postnatal Organ Development as a Complicating Factor in Juvenile Toxicity Studies in Rats

Toxicologic pathologists must evaluate tissues of immature animals from a number of types of nonclinical toxicity studies. The pathologist who is familiar with normal postnatal organ development is in a better position to appropriately detect and differentiate between abnormal, delayed, or precocious development. Vacuolation and apoptosis in multiple tissue types are normal components of development that could influence the interpretation of some tissues. Unique postnatal features such as the germal matrix in the brain, gonocytes in the testes, and saccules in the lung may complicate the histopathological evaluation. With the knowledge of normal organ development and critical windows therein, it is possible to design targeted studies to identify xenobiotic toxicity.

Dietary taurine impairs intestinal growth and mucosal structure of broiler chickens by increasing toxic bile acid concentrations in the intestine

Three experiments were conducted to determine the effect of taurine on the intestinal development, bile acid concentrations, and hormonal status of chickens. In experiment 1, a total of 250 one-day-old broilers were randomly allocated to 5 treatments and supplemented with 0, 0.25, 0.50, 1.00, and 2.00 g/kg of taurine, respectively. Growth performance, weight and length of the small intestine, and intestinal morphology were measured on d 7, 22, and 44. The gene expression levels of several hormones, including epidermal growth factor and cholecystokinin, were also evaluated. In experiment 2, 60 one-day-old broilers were supplemented with 0, 1.0, and 5.0 g/kg of taurine to assess cell proliferation in the jenunal crypt. In experiment 3, 100 newly hatched broilers were assigned randomly to 5 treatments (0, 0.10, 0.50, 2.00, 8.00 g/kg of taurine) to evaluate the bile acid concentrations in the jejunal mucosa. Our results indicated that dietary taurine decreased the length and weight of small intestine, the villus width, surface area, and crypt depth in the duodenum and jejunum (P < 0.05). Taurine also increased the expression of cholecystokinin and epidermal growth factor on the jejunal mucosa (P < 0.001). Taurine has little effect on stimulating the proliferation of intestinal crypt cells, except for 5 g/kg of taurine supplementation on d 14 (P < 0.05). Additionally, a linear increase in the jejunal concentrations of taurocholic acid, taurochenodeoxycholic acid, and taurolithocholic acid was observed on d 7 in broilers fed increasing levels of taurine. In conclusion, we suggested that taurine impairs intestinal mucosal development partly through generation of toxic bile acids.

Effects of an organic acid mixture and methionine supplements on intestinal morphology, protein and nucleic acids content, microbial population and performance of broiler chickens

A study was carried out to investigate the effects of dietary supplementation of an organic acids mixture and two methionine supplements on intestinal morphology, protein and nucleic acids content, microbial population and performance of broiler chickens. Six hundred unsexed day-old Ross 308 broiler chicks were used in a factorial arrangement (3 × 2) based on a completely randomised design by four replicates with 25 chicks in each. Experimental diets consisted of: 0% organic acid mixture + DL-methionine (Treatment 1), 0% organic acid mixture + Alimet (Treatment 2), 0.5% organic acid mixture + DL-methionine (Treatment 3), 0.5% organic acid mixture + Alimet (Treatment 4), 1% organic acid mixture + DL-methionine (Treatment 5) and 1% organic acid mixture + Alimet (Treatment 6). A significant increase in jejunum mucosal DNA content was found by using 1% of organic acid mixture compared with those by other levels of organic acids at 21 days of age (P < 0.05). Also Treatments 5 and 6 had a higher mucosal DNA content than other treatments (P < 0.05) in a similar period. While at grower stage, the results have shown that protein content, protein/DNA and protein/RNA ratio by 0.5 and 1% of organic acids mixture significantly increased compared with those in the 0% level (P < 0.05). The addition of 1% level of organic acid mixture significantly increased villus height compared with 0 and 0.5% level of organic acid mixture at 21 days of age (P < 0.05). Highest and lowest villus heights were obtained by Treatments 1 and 6 (P < 0.05). Crypt depth increased by 0.5 and 1% of organic acid at 21 and 42 days of age (P < 0.05). Villus surface was significantly increased by 1% of organic acid mixture compared with that by 0% level at 21 days of age. The use of organic acid levels especially 1% resulted in an increase in lactic acid bacteria and decreased Enterobacteriaceae counts in the ileum of broiler chicken (P < 0.05). Better bodyweight and feed conversion ratio were obtained (P < 0.05) by 0.5 and 1% of organic acids mixture, although no response was found in feed intake and mortality in this respect (P > 0.05). The results of this study have shown improved reactions on intestinal morphometrical parameters and microflora atmosphors, by using 1% organic acid mixture. In contrast no differences were found between Alimet and DL-methionine in all tested parameters.

Epidermal growth factor and parathyroid hormone-related peptide mRNA in the mammary gland and their concentrations in milk: effects of postpartum hypoxia in lactating rats

The physiological adaptations of the neonatal rat to hypoxia from birth include changes in gastrointestinal function and intermediary metabolism. We hypothesized that the hypoxic lactating dam would exhibit alterations in mammary gland function leading to changes in the concentration of milk peptides that are important in neonatal gastrointestinal development. The present study assessed the effects of chronic hypoxia on peptides produced by the mammary glands and present in milk. Chronic hypoxia decreased the concentration of epidermal growth factor (EGF) in expressed milk and pup stomach contents and decreased maternal mammary gland EGF mRNA. The concentration of parathyroid hormone-related protein (PTHrp) was unchanged in milk and decreased in pup stomach contents; however, mammary PTHLH mRNA was increased by hypoxia. There was a significant increase in adiponectin concentrations in milk from hypoxic dams. Chronic hypoxia decreased maternal body weight, and pair feeding normoxic dams an amount of food equivalent to hypoxic dam food intake decreased body weight to an equivalent degree. Decreased food intake did not affect the expression of EGF, PTHLH, or LEP mRNA in mammary tissue. The results indicated that chronic hypoxia modulated mammary function independently of hypoxia-induced decreases in maternal food intake. Decreased EGF and increased adiponectin concentrations in milk from hypoxic dams likely affect the development of neonatal intestinal function.

Oral administration of spermine advances intestinal maturation in sucking piglets

The objective of this study was to investigate the effect of orally administered spermine at various doses on intestinal maturation in sucking piglets. Thirty-six 11-day-old sucking piglets were assigned randomly to one of six treatments to receive via a stomach tube 0, 0·1, 0·2, 0·3, 0·4, or 0·5 mmol spermine per kg live weight (LW) per day for 3 days. At day 14 of age, duodenum, jejunum and ileum were obtained for biochemical and morphological analysis. Increasing the dose of orally administered spermine increased intestinal weight (linear effect, P<0·01), mucosal weight (linear effect, P<0·05), and mucosal protein, DNA and RNA contents of the duodenum (linear effect, P≤0·01) and jejunum (linear effect, P<0·01). Elevating spermine doses also enhanced (linear effect, P≤0·02) the specific activities of maltase and sucrase but decreased (linear effect, P<0·01) lactase specific activity in the jejunum and duodenum. Furthermore, augmenting oral doses of spermine increased crypt depth and villus width but reduced villus height in the jejunum (linear effect, P<0·05) and duodenum (linear effect, P<0·01). For most measurements, the effects were observed at the oral spermine doses of 0·3 to 0·5 mmol/kg LW per day. Collectively, the results show that oral administration of optimal doses of spermine to 11-day-old sucking piglets induces precocious intestinal maturation and promotes intestinal growth.

Changes in tissue nucleic acid content and mucosal morphology during intestinal development in pouch young of the tammar wallaby (Macropus eugenii eugenii)

DNA and RNA content and the timing of development of various histological features in the small and large intestine of in-pouch tammar wallabies (Macropus eugenii eugenii) of various ages were measured. A significant decline in gut tissue DNA concentrations and increase in the RNA/DNA ratios over 300 days postpartum indicated that the early postnatal increase in gut tissue mass resulted largely from hypertrophy. Mean duodenal and ileal villus height and crypt depth were significantly greater for in-pouch young aged >100 days compared with those <100 days and were significantly greater in the duodenum than in the ileum. Goblet cells appeared more slowly during development and were fewer in number in the duodenal than in the colonic mucosa. The numbers of mucin-secreting duodenal goblet cells were greater in pouch young aged >100 days than in young aged <100 days. The colonic mucosa exhibited no villi or villus-like folds. Colonic crypt depth increased uniformly with age.

Body and intestinal growth of broiler chicks on a commercial starter diet. 1. Intestinal weight and mucosal development

1. A study was conducted on the pattern of development of the intestinal mucosa of the Steggles x Ross (F1) strain of broiler chickens reared on a commercial starter diet. The mechanisms underlying the structural changes were also assessed. 2. In relation to body weight, small intestinal weight peaked at 7 d of age and declined subsequently. There was also a reduction in the relative weights of the gizzard and yolk sac with age. The length of the small intestine and its regions increased with age. 3. Crypt depth increased with age in the duodenum and jejunum while villus height increased significantly with age in all three regions of the small intestine. There were also significant changes in apparent villus surface area in the three regions, while interactions between age and intestinal region were significant in the case of crypt depth and villus height. 4. There were significant differences between the age groups in the mucosal protein content of jejunal and ileal homogenates, both tending to peak at 7 d of age. The DNA content of the intestinal mucosa declined with age in the three regions of the small intestine. While there was an increase in RNA content in the duodenum and ileum, there was a reduction in the jejunum. 5. Protein: DNA ratio increased between hatch and 21 d of age in all intestinal regions. Protein: RNA ratio decreased with age in the duodenum and ileum but increased in the jejunum. There were significant increases in RNA: DNA ratio in the duodenum and ileum but no changes were observed in the jejunum. The interactions between age and intestinal region were significant for all biochemical indices assessed. 6. At all ages, enterocyte proliferation at the jejunum was completed and quantifiable within 1 h of administration of 5-bromo-2'-deoxyuridine (BrDU). Subsequent assessment revealed an increase in crypt column count and number of BrDU-labelled cells. The rate of cell migration increased with age while there was a decline in the distance migrated in proportion to mucosal depth. The estimated life-span of enterocytes and time spent by enterocytes in the crypt varied with age. In d-old and 7-d-old chicks, migration was complete or nearly complete within 96 h of cell birth. 7. Although the intestinal mucosa of the strain was structurally developed at hatch, there was much change in structure with age, especially over the first 7 d post hatch. The rate of development was most rapid in the jejunum but the other regions are also important, on account of villus height or relative length of the region.