Administration of insulin-like growth factor-I (IGF-I) peptides for three days stimulates proliferation of the small intestinal epithelium in rats

Effects of weaning on intestinal crypt epithelial cells in piglets

Intestinal epithelial cells in the crypt proliferate in piglets in response to weaning. However, the underlying mechanism has been unclear. We examined 40 piglets from eight litters (five piglets per litter) that were weaned at the age of 14 d, and one piglet from each litter was randomly selected for closer investigation. Based on the distended intestinal sac method, we isolated crypt epithelial cells from the mid-jejunum on Days 0, 1, 3, 5, and 7 post-weaning. Protein expression was analyzed using either isobaric tags for relative and absolute quantification or western blotting. Proteins related to the cell cycle, organization of the cellular macromolecular complex subunit, localization of cellular macromolecules, Golgi vesicle transport, fatty acid metabolism, oxidative phosphorylation, and translational initiation were mainly down-regulated, while those involved in glycolysis, cell cycle arrest, protein catabolism, and cellular amino acid metabolism were up-regulated. The amount of proteins active in the mTOR signaling pathway was generally decreased over time. These results indicate that weaning influences energy metabolism, cellular macromolecule organization and localization, and protein metabolism, thereby affecting the proliferation of intestinal epithelial cells in weaned piglets. Moreover, those cellular processes are possibly controlled by that signaling pathway.

IGF1 stimulates crypt expansion via differential activation of 2 intestinal stem cell populations

Insulin-like growth factor 1 (IGF1) has potent trophic effects on normal or injured intestinal epithelium, but specific effects on intestinal stem cells (ISCs) are undefined. We used Sox9-enhanced green fluorescent protein (EGFP) reporter mice that permit analyses of both actively cycling ISCs (Sox9-EGFP(Low)) and reserve/facultative ISCs (Sox9-EGFP(High)) to study IGF1 action on ISCs in normal intestine or during crypt regeneration after high-dose radiation-induced injury. We hypothesized that IGF1 differentially regulates proliferation and gene expression in actively cycling and reserve/facultative ISCs. IGF1 was delivered for 5 days using subcutaneously implanted mini-pumps in uninjured mice or after 14 Gy abdominal radiation. ISC numbers, proliferation, and transcriptome were assessed. IGF1 increased epithelial growth in nonirradiated mice and enhanced crypt regeneration after radiation. In uninjured and regenerating intestines, IGF1 increased total numbers of Sox9-EGFP(Low) ISCs and percentage of these cells in M-phase. IGF1 increased percentages of Sox9-EGFP(High) ISCs in S-phase but did not expand this population. Microarray revealed that IGF1 activated distinct gene expression signatures in the 2 Sox9-EGFP ISC populations. In vitro IGF1 enhanced enteroid formation by Sox9-EGFP(High) facultative ISCs but not Sox9-EGFP(Low) actively cycling ISCs. Our data provide new evidence that IGF1 activates 2 ISC populations via distinct regulatory pathways to promote growth of normal intestinal epithelium and crypt regeneration after irradiation.

Insulin-like growth factors in the gastrointestinal tract and liver

The liver is a major source of insulin-like growth factors (IGFs) and IGF binding proteins (IGFBPs) that are present in the circulation and have important endocrine activities relating to energy metabolism, body size, carcinogenesis, and various organ-specific functions. Although IGFs have only minor effects on the normal liver itself, production of IGFs and IGFBPs in a tissue-specific manner in the gastrointestinal tract exert important regulatory effects on cellular proliferation, survival, and apoptosis. IGFs and IGFBPs play important regulatory roles in the response of both the liver and the gastrointestinal tract to inflammation and in the development of neoplasia.

Insulin glargine and NPH insulin increase to a similar degree epithelial cell proliferation and aberrant crypt foci formation in colons of diabetic mice

The insulin analog glargine has a higher binding affinity than regular insulin for the insulin-like growth factor 1 receptor in vitro, raising questions about increased mitogenicity in vivo. Observational studies in humans have recently reported a potential differential association between insulin glargine and malignancies, but available evidence remains inconclusive. We directly compared glargine vs. neutral protamine Hagedorn (NPH) insulin's effects on cell proliferation in colonic mucosa and on formation of aberrant crypt foci in diabetic mice, i.e., early stages of colorectal cancer development. Mice (BKS.Cg-+Lepr(db)/+Lepr(db)/OlaHsd) were treated with insulin glargine (G), NPH insulin (NPH), or saline (NaCl). We assessed epithelial proliferation after long-term insulin treatment (18 weeks) by 5-bromo-2'-deoxyuridine and Ki67 staining and analyzed the formation of aberrant crypt foci (ACF) in mice treated with insulin glargine or NPH insulin or 10 weeks after initiation with 1,2-dimethylhydrazine. Insulin glargine treatment did not result in significantly different epithelial colonic proliferation compared to NPH insulin (G, 137 ± 22; NPH, 136 ± 15; NaCl, 100 ± 20 (relative proliferation index)), but both insulin-treated groups of mice had a higher proliferation index compared to the NaCl control group (p<0.001). Similarly, we observed no difference in ACF formation between glargine- and NPH-insulin-treated mice (G, 132 ± 12; NPH, 138 ± 9; NaCl, 100 ± 7 (relative number of ACF)), but ACF formation was significantly higher in insulin-treated mice than in NaCl-treated control mice (p=0.001). Chronic insulin treatment results in higher colonic epithelial proliferation and ACF formation, but the use of insulin glargine vs. NPH insulin is not associated with increased risk.

Integration of endocrine and mechanical signals in the regulation of myometrial functions during pregnancy and labour

In this review, we describe a new model to explain the regulation of myometrial function during pregnancy and labour. We propose that the myometrium undergoes dramatic changes in phenotype from early pregnancy until the onset of labour, characterized by an early proliferative phase, an intermediate phase of cellular hypertrophy and matrix elaboration, a third phase in which the cells assume a contractile phenotype and the final phase in which cells become highly active and committed to labour. The last phase of myometrial differentiation is postpartum uterine involution, completing the reproductive cycle following pregnancy and labour by returning the uterus to its non-pregnant receptive state. We further propose that phenotypic modulation of the uterine myocytes is the result of integration of endocrine signals and mechanical stimulation of the uterus by the growing fetus. Our previous studies have shown that these signals are important in regulating the onset of labour and we now have indications that they regulate earlier myometrial smooth muscle differentiation. We show that the high rate of myometrial cell proliferation in early pregnancy which reflects important aspects of many smooth muscle populations during development. The proliferative phenotype was associated with dramatic changes in the expression of IGF family proteins and coincided with an up-regulation of the anti-apoptotic pathway. Preliminary evidence suggests that myometrial hyperplasia was controlled by the PI3K-Akt-mTOR signaling pathway. The modulation of the mTOR pathway by rapamycin blocked the proliferative activity of the uterine myocytes. The growth and remodeling of the myometrium during pregnancy was associated with increased synthesis of extra cellular matrix (ECM) proteins and their corresponding integrin receptors. Our results show a decrease in expression of fibrillar collagens and a coordinated temporal increase in expression of components of the basement membrane near term associated with decreased progesterone levels and increased mechanical tension. The phenotypic modulation of uterine smooth muscle cells during pregnancy culminates at term when a myometrium-specific conversion commits these cells to the labour phenotype, characterized by increased excitability, spontaneous activity, responsiveness to agonists and effective coupling of the myocytes. The reinforcement of the ECM-integrin interaction contributes to myometrial hypertrophy and remodeling during late pregnancy and facilitates force transduction during the contractions of labour by anchoring hypertrophied SMCs to the uterine ECM. In addition, we suggest that myometrial cells play an important role in the generation and regulation of uterine inflammation, which is a characteristic feature of parturition. We provide here substantial evidence that myometrial cells can actively participate in the inflammatory process in the uterus by the release of the pro-inflammatory chemokine MCP-1. The increased production of MCP-1 in the term myometrium was associated with uterine occupancy and regulated by progesterone, suggesting that mechanical and endocrine signals integrate to regulate the expression of the chemokine and the induction of labour. A better understanding of the mechanisms regulating myometrial differentiation during pregnancy might inform the development of new therapeutic strategies for the management of preterm labour, which remains a leading cause of neonatal morbidity and mortality. Our data are obtained mostly from the rat, but we believe that they are generally applicable across species.

Effect of IGF-I on healing of colonic anastomoses in rats under 5-FU treatment

BACKGROUND

The aim of this experimental study was to investigate whether insulin-like growth factor I (IGF-I) can protect the colonic healing from the adverse effects of intraperitoneal administration of 5-fluorouracil (5-FU).

MATERIALS AND METHODS

Eighty male Wistar rats were randomized into four groups of 20 rats each. Immediately after anastomoses were performed, rats in the control group were injected with 1 mL/100 gr of intraperitoneal saline solution, which was repeated daily until killed. Rats in the 5-FU and IGF-I +5-FU groups received 5-FU in a dose of 20 mg/kg body weight intraperitoneally, from the day of operation until killed. Rats in the IGF-I and IGF-I +5-FU groups received IGF-I in a dose of 2 mg/kg body weight intraperitoneally, immediately after the colonic anastomosis was performed and on 2nd, 4th, and 6th postoperative day. Rats were sacrificed on the 7th postoperative day.

RESULTS

The dehiscence rate in the 5-FU group was 30% and it was significantly higher compared with the control and the IGF-I group (P = 0.020 for both comparisons). However, in the IGF-I +5-FU group, the dehiscence rate decreased to 10%. The administration of IGF-I resulted in a significant rise of bursting pressure in the IGF-I +5-FU group compared with the 5-FU group (P < 0.001). There was no statistical difference in bursting pressure between the IGF-I +5-FU and control groups (P = 1.000). The hydroxyproline levels were higher in the IGF-I and the IGF-I +5-FU groups as a result of the stimulating act of IGF-I.

CONCLUSION

IGF-I, when given intraperitoneally, seems to mediate some of the adverse effects of 5-FU on the colonic healing in rats.

Contribution of insulin-like growth factor I to the healing of colonic anastomoses in rats

The aim of this experimental study was to investigate the contribution of insulin-like growth factor I (IGF)-I in the colonic healing process when injected intraperitoneally after colon resection. Forty male Wistar rats were used. Rats in the control group were injected with 3 mL of a solution of 0.9% NaCl intraperitoneally after the operation and on postoperative day 2, 4, and 6. Rats in the IGF-I group received recombinant human IGF-I in a dose of 2 mg/kg body weight intraperitoneally, immediately after the colonic anastomosis was performed and on postoperative day 2, 4, and 6. All rats were killed on postoperative day 7. The hydroxyproline tissue content was significantly higher in the IGF-1 group than in the control group. The bursting pressures were also significantly higher in IGF-1 group than in the control group. The weight change between the groups differed significantly; in the control group the average weight decreased about 5% postoperatively, while in the IGF-1 group the average weight increased about 6%. The average inflammatory cell infiltration score was significantly higher in the control group. Neoagiogenesis did not differ significantly between the two groups. The fibroblast activity differed significantly between the two groups, as the control group had significantly less fibroblasts compared to the IGF-1 group. In conclusion, IGF-I when given intraperitoneally stimulates the healing of colonic anastomoses in the rats. Further studies are required in order to determine whether this effect is dose related.

Suppressor of cytokine signaling-2 limits intestinal growth and enterotrophic actions of IGF-I in vivo

Suppressors of cytokine signaling (SOCS) typically limit cytokine receptor signaling via the JAK-STAT pathway. Considerable evidence demonstrates that SOCS2 limits growth hormone (GH) action on body and organ growth. Biochemical evidence that SOCS2 binds to the IGF-I receptor (IGF-IR) supports the novel possibility that SOCS2 limits IGF-I action. The current study tested the hypothesis that SOCS2 normally limits basal or IGF-I-induced intestinal growth and limits IGF-IR signaling in intestinal epithelial cells. Intestinal growth was assessed in mice homozygous for SOCS2 gene deletion (SOCS2 null) and wild-type (WT) littermates at different ages and in response to infused IGF-I or vehicle or EGF and vehicle. The effects of SOCS2 on IGF-IR signaling were examined in ex vivo cultures of SOCS2 null and WT intestine and Caco-2 cells. Compared with WT, SOCS2 null mice showed significantly enhanced small intestine and colon growth, mucosal mass, and crypt cell proliferation and decreases in radiation-induced crypt apoptosis in jejunum. SOCS2 null mice showed significantly greater growth responses to IGF-I in small intestine and colon. IGF-I-stimulated activation of IGF-IR and downstream signaling intermediates were enhanced in the intestine of SOCS2 null mice and were decreased by SOCS2 overexpression in Caco-2 cells. SOCS2 bound directly to the endogenous IGF-IR in Caco-2 cells. The intestine of SOCS2 null mice also showed enhanced growth responses to infused EGF. We conclude that SOCS2 normally limits basal and IGF-I- and EGF-induced intestinal growth in vivo and has novel inhibitory effects on the IGF-IR tyrosine kinase pathway in intestinal epithelial cells.

Effects of Oral Administration of Insulin-Like Growth Factor-I on Circulating Concentration of Insulin-Like Growth Factor-I and Growth of Internal Organs in Weanling Mice

Insulin-like growth factor (IGF)-I is a polypeptide that mediates the growth-promoting action of growth hormone in postnatal animals. The present study was conducted to examine whether orally administered IGF-I would be absorbed into the general circulation and also whether ingested IGF-I would enhance the growth of whole body as well as internal organs, and tissues in 3-week-old ICR-strain female weanling mice. In experiment (Exp) 1, a total of 70 mice received IGF-I orally at 1 microg.g-1 in 0.2-ml PBS or the vehicle alone. Concentrations of IGF-I and glucose in heart blood were measured after killing 5 animals in each group every fourth hour during a 24-hour period. In Exp 2, a total of 40 mice received oral IGF-I administration at 1 microg.g-1 or vehicle every third day beginning from day 0 for a 13-day period. Half the animals were killed at day 7 and the other half at day 13. Weights of whole body and organs/tissues (small intestine, liver, thigh muscle, and brain) were measured every day and at slaughter, respectively. In Exp 1, following the oral IGF-I administration, serum IGF-I concentration increased at hour 4 (p<0.01) and returned to the hour 0 level by hour 8, whereas glucose concentration was lowest at hour 4 and returned to the hour 0 level by hour 16. In the PBS-fed group, neither IGF-I nor glucose concentration changed during the 24-hour period. In Exp 2, weight of small intestine increased (p<0.05) in response to the oral IGF-I, whereas weights of liver and thigh muscle of the IGF-I-fed group were greater (p<0.01) and tended to be greater (p=0.06), respectively, than those of the PBS-fed only at day 13. However, brain weight and serum concentrations of IGF-I and IGF-II were not affected by oral IGF-I administration. Results suggest that although orally administered IGF-I mainly acts at the intestine, a portion of ingested IGF-I is absorbed into the general circulation to enhance the growth of selective organs/tissues in weanling mice.

Pre-treatment with insulin-like growth factor-I partially ameliorates 5-fluorouracil-induced intestinal mucositis in rats

Insulin-like growth factor-I (IGF-I) has been demonstrated to enhance mucosal repair following intestinal damage induced by chemotherapeutic agents (intestinal mucositis). However, the potential for prophylactic IGF-I to protect the intestine remains undefined. We investigated the effects of IGF-I pre-treatment on chemotherapy-induced mucositis in rats. Male Sprague Dawley rats were treated for 7 days with 0 or 4.3mg/kg/day IGF-I delivered systemically via osmotic mini-pump. Rats received an intraperitoneal injection of 0 or 150 mg/kg 5-fluorouracil (5-FU) on day 7 and were killed 48 h later for assessment of intestinal damage and repair. Compared to normal controls, 5-FU decreased epithelial proliferation by 86%, concurrently increasing the incidence of apoptosis 87-fold, whilst decreasing small intestinal (SI) length by 14%, SI weight by 30% and total gut weight by 24%. 5-FU decreased villus height in the duodenum (23%), jejunum (20%) and ileum (30%) with crypt depths decreased by 31%, 27% and 33% in these gut regions. These effects were less profound in IGF-I pre-treated rats in which apoptosis was increased 48-fold, with SI length decreased by 7%, SI weight by 18% and total gut weight by 15% accompanied by decreases in villus height of 8% (duodenum), 14% (jejunum) and 21% (ileum), and crypt depth decreases of 23%, 16% and 17% for the same gut regions, compared to normal controls. We conclude that IGF-I pre-treatment only partially attenuates features of intestinal mucositis when assessed 48 h after 5-FU chemotherapy.

Relative expression and localization of the insulin-like growth factor system components in the fetal, child and adult intestine

BACKGROUND

The insulin-like growth factors (IGFs) are important in the development and maintenance of the gastrointestinal tract.

OBJECTIVES

To compare the expression of IGFs and their receptors in the stomach and duodenum of the fetus, the child and the adult. To identify the cells mainly responsible for the production of the members of the IGF system.

METHODS

Tissue was obtained from fetus after abortion and from children and adults during diagnostic endoscopy and biopsy. The expression of the IGFs and their receptors was estimated by an RNAse protection assay and sections were stained with antisera to the components of IGF system.

RESULTS

The tissues from the stomach and the duodenum expressed the two IGFs and their receptors at all stages of life. The fetal IGF receptors I and II, were approximately ten times higher than in the child and IGF-II was five times higher. Immunohistochemical staining showed the components of the IGF system to be localized to the gastric glands and to the basotlateral border of the gastric epithelial cells. In the duodenum, they were concentrated at the apical portion of the epithelial tissue. They could also be identified in ganglion cells and nerves.

CONCLUSIONS

The IGFs and their receptors in the stomach and duodenum are expressed in all age groups and mostly are highest in the fetus. The IGF system proteins were located in the gastric glands and epithelium and in the apical portion of the villous epithelium of the duodenum.

Jejunal microvilli atrophy and reduced nutrient transport in rats with advanced liver cirrhosis: improvement by Insulin-like Growth Factor I

Background

Previous results have shown that in rats with non-ascitic cirrhosis there is an altered transport of sugars and amino acids associated with elongated microvilli. These alterations returned to normal with the administration of Insulin-Like Growth Factor-I (IGF-I). The aims of this study were to explore the evolution of these alterations and analyse the effect of IGF-I in rats with advanced cirrhosis and ascites. Thus, jejunal structure and nutrient transport (D-galactose, L-leucine, L-proline, L-glutamic acid and L-cystine) were studied in rats with ascitic cirrhosis.

Methods

Advanced cirrhosis was induced by CCl₄ inhalation and Phenobarbital administration for 30 weeks. Cirrhotic animals were divided into two groups which received IGF-I or saline during two weeks. Control group was studied in parallel. Jejunal microvilli were studied by electron microscopy. Nutrient transport was assessed in brush border membrane vesicles using ¹⁴C or ³⁵S-labelled subtracts in the three experimental groups.

Results

Intestinal active Na⁺-dependent transport was significantly reduced in untreated cirrhotic rats. Kinetic studies showed a decreased V_max and a reduced affinity for sugar and four amino acids transporters (expressed as an increased K_t) in the brush border membrane vesicles from untreated cirrhotic rats as compared with controls. Both parameters were normalised in the IGF-I-treated cirrhotic group. Electron microscopy showed elongation and fusion of microvilli with degenerative membrane lesions and/or notable atrophy.

Conclusions

The initial microvilli elongation reported in non ascitic cirrhosis develops into atrophy in rats with advanced cirrhosis and nutrient transports (monosaccharides and amino acids) are progressively reduced. Both morphological and functional alterations improved significantly with low doses of IGF-I.

Effects of enterally administering granulocyte colony-stimulating factor to suckling mice

Gastrointestinal (GI) tract development is influenced by multiple growth factors, some of which are delivered directly to the GI lumen, as they are swallowed constituents of amniotic fluid, colostrum, and milk. Granulocyte colony-stimulating factor (G-CSF), traditionally known as a granulocytopoietic growth factor, is an example of one such factor. However, it is not clear whether the large amounts of G-CSF that are normally swallowed by the fetus and neonate have systemic effects on circulating neutrophils or local effects in the developing intestine. To assess this, we administered either active or heat-denatured (control) recombinant human G-CSF to 5- to 7-d-old C57BL/6 x 129SvJ mice. Pups received either a low dose (3 ng) that was calculated to approximate the amount of G-CSF swallowed in utero from amniotic fluid or an isovolemic high dose 100 times larger (300 ng). Oral dosing was performed daily for either 3 or 7 d, after which pups were killed and measurements were made on the blood and the GI tract. Absolute blood neutrophil counts and immature to total neutrophil ratios did not differ from controls in any of the test groups. However, intestinal villus area, perimeter, length, crypt depth, and proliferating cell nuclear antigen index increased significantly among those that were treated with active G-CSF. Thus, in suckling mice, enterally administered G-CSF had no effect on the concentration of circulating neutrophils but had trophic effects on the intestine. We speculate that the G-CSF present in amniotic fluid, colostrum, and milk acts as a topical intestinal growth factor and has little or no granulocytopoietic action.

Bax is required for resection-induced changes in apoptosis, proliferation, and members of the extrinsic cell death pathways

BACKGROUND AND AIMS

To define better the homeostatic mechanisms contributing to small intestinal adaptation following partial resection, the relative contributions of apoptosis, cell proliferation, and enterocyte migration and the comparative roles of the intrinsic (mitochondrial) and extrinsic (death receptor-mediated) apoptotic pathways were assessed.

METHODS

After 50% jejunoileal resections or transections, adaptation was analyzed in duodenal-jejunal and ileal segments from C57BL/6 Bax(+/+) (16, 48, and 168 hours postoperative) and Bax(-/-) mice (168 hours).

RESULTS

Basal apoptotic rates were equivalent in all mice. By 1-week postresection, villus heights and crypt depths were increased in the duodenal-jejunal and ileal remnants of both genotypes. In Bax(+/+) mice, adaptation occurred in concert with increased crypt proliferative and apoptotic indices. Bax(-/-) mice did not show increases in proliferation or apoptosis, yet adaptive increases in villus height were enhanced relative to Bax(+/+) mice. Enterocyte migration increased in both genotypes. Postresection, the expression of caspases and genes involved in death receptor-mediated apoptosis was decreased in Bax(-/-) compared with Bax(+/+) mice.

CONCLUSIONS

Postresection adaptation involves parallel changes in crypt proliferation and apoptosis, but, as observed in Bax(-/-) mice, it can occur without increased proliferation. These studies demonstrate that spontaneous gut apoptosis is Bax independent, whereas adaptation-related apoptosis is Bax-dependent. Differences between resected Bax(+/+) and Bax(-/-) mice suggest that apoptosis in the adapting gut utilizes the extrinsic pathway, but this requires linkage to the mitochondrial pathway via Bax. The increased adaptive response in Bax(-/-) mice indicates that modulation of apoptosis may be useful for enhancing adaptation.

IGF-I augments resection-induced mucosal hyperplasia by altering enterocyte kinetics

Our objective was to determine if exogenous insulin-like growth factor-I (IGF-I) augments the adaptive growth response to mid small bowel resection in association with changes in enterocyte kinetics. We determined structural adaptation and concomitant changes in enterocyte proliferation, apoptosis, and migration of the jejunum in growing, parenterally fed rats after mid small bowel resection or small bowel transection, and treatment with IGF-I or vehicle. IGF-I treatment in resected rats significantly increased jejunal mucosal mass by 20% and mucosal concentrations of protein and DNA by 36 and 33%, respectively, above the response to resection alone. The enhancement of resection-induced adaptive growth and cellularity by IGF-I reflected an increase in enterocyte proliferation, an expansion of the proliferative compartment in the crypt, and no further decrease in enterocyte apoptosis or increase in enterocyte migration beyond the effects of resection. The ability of IGF-I to augment the mucosal hyperplasia stimulated by the endogenous response to resection substantiates the role of IGF-I as an intestinal mitogen that promotes tissue regeneration.

Distribution of insulin like growth factor-1 (IGF-1) and its receptor in the intestines of the one-humped camel (Camelus dromedarius)

The distribution of insulin-like growth factor-1 (IGF-1) and its receptor in the gut of the one-humped camel (Camelus dromedarius) were studied by immunohistochemistry and quantitative receptor autoradiography. IGF-1-IR cells occurred mainly in the lamina propria and epithelium of the small intestine, while in the large intestine positive cells were seen in the columnar cells of the epithelial layer of colonic glands. IGF-I was also discernible in the muscularis externa of the intestines. Autoradiography revealed a higher concentration of receptors in the mucosa compared to the muscular layer. With regard to the mucosa, the highest density of receptors was discernible in the duodenum. Immunohistochemistry revealed the main sites of the receptors to be the lamina propria, epithelia of the crypts and the villi of intestines. Double immunofluorescence studies with combined antisera to IGF-I and its receptor showed that the ligand and its receptor usually occurred within the same cell in the mucosa. A few cells with varied profiles immunoreacted to either the ligand or the receptor but not to both. Cells with varied profiles immunoreacted to antiserum of the receptors but not to the ligand in the muscle layer. Thus IGF-1 might be acting on its receptor via both an autocrine and paracrine modes in the camel mucosa. In the muscularis layer, IGF-1 may be acting by different mechanisms. Our data demonstrate that unlike all other mammals studied, the camel contains a high concentration of IGF-1 receptors in the duodenal mucosa compared to other parts of the camel gut. It also possesses a higher concentration of the receptor in its mucosa compared to the muscle layer. We speculate that this might be a significant feature necessary for the regenerative ability of the duodenal mucosa in the one-humped camel.

Intestinal morphology, epithelial cell proliferation, and absorptive capacity in neonatal calves fed milk-born insulin-like growth factor-I or a colostrum extract

Concentrations of nonnutritional factors, such as insulin-like growth factor-I (IGF-I), in bovine colostrum are high and can modulate neonatal gastrointestinal tract development and function. In neonatal calves, we have investigated effects on intestinal epithelial cell morphology, proliferation, and absorption of feeding milk-born human IGF-I (hIGF-I) or a bovine colostrum extract. Calves were fed a milk-based formula containing amounts of nutrients comparable to colostrum for the first 3 d and a milk replacer from d 4 on. Formula and milk replacer contained only traces of nonnutritional factors. In experiment 1, supraphysiological amounts of hIGF-I (3.8 mg/L formula; secreted by transgenic rabbits with their milk) were added to the formula. Xylose appearance in blood (after feeding xylose on d 5) and intestinal traits (after euthanasia on d 8) did not differ between groups. In experiment 2, an extract of first-milked bovine colostrum that provided physiological amounts of IGF-I (0.50, 0.15, and 0.09 mg of IGF-I/L formula on d 1, 2, and 3, respectively, and 0.09 mg of IGF-I/L milk replacer on d 4) was added to formula or milk replacer. Plasma xylose concentration in the control group was transiently higher than in calves fed the colostrum extract. On d 5 (after euthanasia), villus circumferences and heights in small intestine, and epithelial cell proliferation rate in intestine were higher in calves fed the colostrum extract than in controls. In conclusion, orally administered hIGF-I from transgenic rabbits had no effect on the intestinal tract. However, feeding a bovine colostrum extract enhanced intestinal villus size, although it appeared to transiently decrease the absorptive capacity.

Tolerance of simulated amniotic fluid in premature neonates

OBJECTIVE

To assess the tolerance of simulated amniotic fluid enterally administered in premature neonates.

DESIGN

A multicentered, Phase I, dose-escalation trial was accomplished among 30 preterm neonates. Groups of 10 patients received 5, 10, or 20 mL/kg/d enterally of the amniotic fluid solution, divided into every-3-hour dosing, for 3 days.

MAIN OUTCOME MEASURES

Amount and character of emesis, stools, and gastric residuals; changes in abdominal girth; presence of a skin rash; blood pressure instability; the diagnosis of necrotizing enterocolitis (NEC) or intestinal perforation.

RESULTS

Thirty patients were studied: 10 received 5 mL/kg/d, 10 received 10 mL/kg/d, and 10 received 20 mL/kg/d of amniotic solution. Gestational ages ranged from 25 to 31 weeks. The Data Safety and Monitoring Board met after each group of 10 patients completed the study, reviewed the outcome measurements, and recommended continuance of the study. Dosing was discontinued for 3 patients prior to receiving all 24 doses because of gastric residuals (n = 1; 5 mL/kg), stage I NEC (n = 1; 10 mL/kg), or symptomatic patent ductus arteriosus (n = 1; 20 mL/kg). The remaining patients completed the doses with no evidence of intolerance: specifically, no increased gastric residuals, increased abdominal girth, diarrhea, blood pressure change, rash, NEC, or intestinal perforation.

CONCLUSIONS

Enteral administration of an amniotic fluid-like solution to preterm neonates is well tolerated in doses <or=20 mL/kg/d.

Tolerance of a sterile isotonic electrolyte solution containing select recombinant growth factors in neonates recovering from necrotizing enterocolitis

OBJECTIVE

To assess the tolerance of a sterile isotonic electrolyte solution containing select recombinant growth factors enterally administered in neonates who were NPO because of necrotizing enterocolitis (NEC).

STUDY DESIGN

A phase I trial was accomplished among 30 neonates. Patients received 5, 10, or 20 mL enterally of the study solution/kg/day divided into every 3-hour dosing, for 3 days prior to when feedings of milk were to resume. The occurrence of emesis, gastric residuals, diarrhea, bloody stools, abdominal distention, skin rashes and death were sought.

RESULTS

Gestational ages ranged from 25.2 to 41.1 weeks. A total of 16 neonates had Stage IA NEC, six Stage IB, and eight Stage IIA. The solution was well tolerated in all 30; none developed diarrhea, guaiac positive or bloody stools, or abdominal distention. Administration of the solution was not prematurely discontinued in any infant. Two neonates died secondary to late-onset sepsis remote from the study period.

CONCLUSIONS

Enteral administration of a sterile isotonic electrolyte solution containing select recombinant growth factors was well tolerated by neonates with NEC.

Effect of breast milk and weaning on epithelial growth of the small intestine in humans

Breast feeding and weaning are important physiologically significant luminal events that influence the growth of the small intestine in humans. A variety of factors including genetic preprogramming, systemic and local hormones, and permissive factors contribute and modulate intestinal growth. Here, we offer a view that integrates some of these factors, especially those relating to breast feeding and weaning.

Intestinal transport of insulin-like growth factor-I (igf-I) in the suckling rat

OBJECTIVES

Insulin-Like Growth Factor-1 is a potent growth-promoting peptide that is present in mammalian milk. Previous studies have suggested that milk-borne IGF-1 may be absorbed intact from the gastrointestinal tract of the suckling but the mechanism responsible for such transport is not well documented. The present study was designed to investigate in an in vivo suckling rat model whether or not intestinal absorption of IGF-1 is a saturable phenomenon.

METHODS

Suckling rats (10-12 days postnatal age) were studied under anesthesia. A jejunal loop from each rat pup was isolated and injected intraluminally with 1-2 x 10 cpm of rh I-IGF-I. Injections were performed in paired littermates either with or without a preceding injection of unlabeled IGF-I of 20, 500, or 1000 ng/ml concentration. After flushing, the loops and livers were homogenized and counted in a gamma counter. In addition, homogenates of jejunum and liver were precipitated with trichloroacetic acid (TCA) and the precipitates also counted. In selected instances (jejunum), acid gel chromatography of homogenates was also performed.

RESULTS

Retention of radioactivity was observed in all jejunal specimens, but the pre-incubation of jejunal loops with unlabeled IGF-1 was associated with a biphasic response, i.e. at low dose (20 ng/ml) pre-incubation limited retention of radioactivity, but at a high dose (1000 ng/ml), retention was enhanced (P < 0.05). Linear regression analysis confirmed this inverse relationship. Liver radioactivity followed a similar pattern. Between 40 and 49% of the radioactivity in jejunal and liver homogenates was TCA precipitable. Chromatography of jejunal homogenates showed that approximately 40% of cpm migrated in a position identical with that of intact IGF-1.

CONCLUSIONS

The intestinal uptake of IGF-1 in the suckling is nonsaturable, confirming previous in vitro studies and suggesting that a nonreceptor-dependent method of transepithelial transport is important in this process.

Insulin and IGF-I inhibit calcium-dependent chloride secretion by T84 human colonic epithelial cells

D-Myo-inositol (3,4,5,6) tetrakisphosphate [Ins(3,4,5,6)P(4)] or phosphatidylinositol 3-kinase (PI 3-kinase) activity acts to inhibit calcium-dependent chloride secretion in T84 colonic epithelial cells. To further distinguish between the contributions of these two signaling pathways to the inhibition of secretion, we studied effects of insulin, because the insulin receptor links to PI 3-kinase but not to pathways postulated to generate Ins(3,4,5,6)P(4). Chloride secretion across T84 cell monolayers was studied in Ussing chambers. Activation of PI 3-kinase was assessed by Western blotting. Basolateral, but not apical, addition of insulin inhibited carbachol- and thapsigargin-induced chloride secretion in a time- and concentration-dependent fashion. Insulin-like growth factor-I (IGF-I) had similar effects. Insulin had no effect on Ins(3,4,5,6)P(4) levels, and the inhibitory effects of insulin and IGF-I on chloride secretion were fully reversed by the PI 3-kinase inhibitors wortmannin and LY-294002. Western blot analysis showed that both insulin and IGF-I recruited the 85-kDa regulatory and 110-kDa catalytic subunits of PI 3-kinase to anti-phosphotyrosine immunoprecipitates. In conclusion, insulin and IGF-I act to inhibit calcium-dependent chloride secretion through a PI 3-kinase-dependent pathway. Because insulin is released in a pulsatile fashion postprandially and IGF-I levels are elevated in pathological settings, our findings may have physiological and/or pathophysiological significance.

Altered intestinal transport of amino acids in cirrhotic rats: the effect of insulin-like growth factor-I

The intestine is an important target organ for insulin-like growth factor-I (IGF-I), an anabolic hormone synthesized in the liver upon growth hormone (GH) stimulation. Levels of IGF-I are reduced in cirrhosis, and altered GH/IGF-I axis may contribute to malnutrition in cirrhotic patients. Our aim was to study Na(+)-dependent jejunal transport of amino acids (L-leucine, L-proline, L-glutamic acid, and L-cysteine) in cirrhotic rats and to analyze the effect of IGF-I on this function. IGF-I or saline was administered for 2 wk to rats with CCl(4)-induced cirrhosis and saline was administered to healthy control rats. Transport of amino acids was assessed in brush-border membrane vesicles (BBMV) using (14)C- or (35)S-labeled amino acids, and the kinetic constants V(max) and K(t) were determined. Na(+)-independent uptake of L-leucine, L-proline, L-glutamic acid, and L-cysteine by BBMV was similar in all groups. Na(+)-dependent uptake of all four amino acids was significantly diminished in cirrhotic rats compared with both controls and IGF-I-treated cirrhotic rats. The latter two groups exhibited similar V(max) and K(t), whereas untreated cirrhotic rats had reduced V(max) and increased K(t) compared with normal controls and IGF-I-treated cirrhotic animals. In conclusion, the transport of all four tested amino acids by BBMV is impaired in cirrhotic rats, and low doses of IGF-I can correct this defect.

Effects of aging on expression of genes involved in regulation of proliferation and apoptosis in the colonic epithelium

The purpose of this study was to characterize the effects of aging on colonic messenger ribonucleic acid (mRNA) and protein levels of genes involved in the regulation of cell proliferation and apoptosis, and epithelial morphology in male Fischer 344 rats. Our study shows that, with aging, colonic expression of insulin-like growth factor-1 (IGF-1) and IGF-binding protein-3 (IGFBP-3) is significantly increased and decreased, respectively. Colonic Bax protein levels are increased significantly with aging. Immunohistochemical localization of Bax protein shows a greatly increased expression in colonic crypts, especially in the upper portion of crypts. p53 expression is unchanged with aging. No significant change in proliferation of colonic crypt cells is observed by bromodeoxyuridine (BrdU) labeling, although the increased colonic expression of IGF-1 and the decreased expression of IGFBP-3 with aging may result in an increased colonic IGF-1 bioactivity. The age-related changes in Bax and IGFBP-3 appear to be independent of p53. The finding of an unchanged colonic epithelium with aging in the face of a greatly increased Bax protein levels may suggest that the elevated Bax protein levels function to render colonic epithelial cells more sensitive to apoptotic stimuli.

Insulin modulates intestinal response of suckling mice to the Escherichia coli heat-stable enterotoxin

Effect of insulin on the response of suckling mice to the enterotoxigenic Escherichia coli heat-stable enterotoxin (STa) was studied. Four groups (8-10 in each group) of two day old Swiss Webster suckling mice were used. Five, 10, 25, and 50 micrograms of insulin were given orally to half the mice in each group respectively. The rest of the mice in each group were given normal saline as intra-litter controls. After 7 days, the suckling mouse assay for STa was performed on three mice from each insulin-treated and control groups. Enterocyte suspensions were prepared from mice in all groups. Intestinal tissue samples were taken for electron microscopy. Interaction of STa with its putative receptor on the enterocytes was evaluated using indirect immunofluorescence and flow cytometry. The suckling mouse assay revealed a significant increase in the gut weight to body weight ratio in all mice in the insulin treated groups compared to control mice (p < 0.05). Flow cytometry and indirect immunofluorescence analyses suggested that insulin had an upregulatory effect on the STa receptor level. Similarly, insulin was found to increase intestinal brush border membrane differentiation as indicated by the increase in the inward movement of milk particles through the intestinal mucosa. Insulin seems to modify the structure-function of the brush border membrane including the response of suckling mice to STa. This study may provide further insights into the mechanism of STa/receptor interaction in diarrhea in newborn animals and human infants.

Stimulatory actions of insulin-like growth factor-I and transforming growth factor-alpha on intestinal neurotensin and peptide YY

Proliferation of the gastrointestinal mucosa is stimulated by the growth factors, insulin-like growth factor-I (IGF-I) and transforming growth factor-alpha (TGF-alpha), or the closely related epidermal growth factor (EGF), as well as the gastrointestinal hormones, gastrin, neurotensin (NT), and peptide YY (PYY). The stimulatory actions of these growth factors or gastrointestinal hormones on the gastrointestinal mucosa may be direct or mediated in part by gastrointestinal peptides or the growth factors, respectively. The purpose of these studies therefore was to examine the effects of IGF-I and TGF-alpha on stomach gastrin and intestinal NT and PYY gene expression [i.e. messenger RNA (mRNA), peptide levels] and secretion. Mice were given recombinant human IGF-I (3, 6 mg/kg BW/day x 14 days). Transgenic mice with the rat TGF-alpha gene linked to a metallothionein promoter were used as a model of chronic TGF-alpha excess. IGF-I and TGF-alpha did not affect gastrin gene expression. Steady-state intestinal NT and PYY mRNA and peptide levels were elevated in a dose-related manner by IGF. TGF-alpha also increased intestinal expression of NT and PYY peptide, but not mRNA levels. Basal serum levels of PYY were elevated by IGF-I and TGF-alpha. IGF-I and TGF-alpha did not increase intestinal chromogranin A (CGA) gene expression, a marker of endocrine cells, or the density of PYY-containing cells in the colon, indicating that the elevations in intestinal gut peptide gene expression by IGF-I and TGF-alpha are not due simply to an increased number of enteroendocrine cells. IV infusion of EGF also stimulated release of PYY in the dog. Together, these findings indicate that IGF-I and TGF-alpha may cause secretion of gut hormones and exert a major upregulatory influence on the regulation of intestinal peptide hormone homeostasis.

Diet fat and oral insulin-like growth factor influence the membrane fatty acid composition of suckling rat small intestine

BACKGROUND

Insulin-like growth factor- plays an important role in small intestine development. The presence of insulin-like growth factor-1 and the complexity of the fatty acid composition in breast milk suggests that intestinal development may be influenced by manipulating the levels of these components.

METHODS

To determine whether a physiological dose of insulin-like growth factor-1 would influence sucrase and lactase activity levels, 10-day-old suckling rat pups were treated with an oral gavage of insulin-like growth factor-1. Four diets differing in fat composition were fed to lactating dams. Brush border membranes were isolated from jejunal and ileal segments of suckling rat small intestine. Fatty acid analysis of choline and ethanolamine phospholipids was performed.

RESULTS

Insulin-like growth factor-1 was found to have no effect on the sucrase and lactase activities of suckling rats. Changes in the diet fat composition of the mother's diet indirectly influenced the fatty acid composition of suckling rat small intestine. Insulin-like growth factor-1 decreased ileal C20:4n-6 levels. A correlation was observed between lactase activity and C20:4n-6 and C22:6n-3 levels. As C20:4n-6 levels increased, lactase activity appeared to decline. Increased lactase activity was observed when C22:6n-3 levels increased.

CONCLUSIONS

The changes observed in C20:4n-6 levels in response to oral insulin-like growth factor-1, combined with the apparent trend of increased lactase activity with declining levels of C20:4n-6, may be of significance in the development of the small intestine in early life.

Effect of insulin-like growth factor I on in vivo intestinal absorption of D-galactose in cirrhotic rats

Insulin-like growth factor I (IGF-I) bioavailability is reduced in liver cirrhosis, a condition frequently associated with malnutrition. We have analyzed in vivo absorption of D-galactose by jejunal loops in rats with CCl4-induced liver cirrhosis and the influence of IGF-I on intestinal sugar transport in this disease. Two different study protocols were followed. In protocol 1, healthy control rats or cirrhotic rats received saline or IGF-I (2 micrograms . 100 g body wt-1. day-1) for 2 wk. In protocol 2, control and cirrhotic rats received saline or IGF-I as a bolus injection of 1 microgram/100 g body wt followed by continuous infusion of the same dose for 100 min. In vivo D-galactose absorption was reduced in cirrhotic rats compared with healthy controls. IGF-I, as both a chronic (protocol 1) and acute treatment (protocol 2), was able to improve sugar transport in cirrhotic rats but had no effect on sugar absorption in healthy rats. A significant elongation of enterocyte microvilli was observed in cirrhotic animals; this alteration was totally or partially corrected by chronic or acute IGF-I administration. Our results show that in vivo jejunal sugar transport and microvilli structure are altered in liver cirrhosis and that IGF-I, among other effects, may correct these changes by modulating cytoskeletal organization in enterocytes.

Systemically but not orogastrically delivered insulin-like growth factor (IGF)-I and long [Arg3]IGF-I stimulates intestinal disaccharidase activity in two age groups of suckling rats

The growth mitogenic properties of IGF-I on tissues of the gastrointestinal tract are well established; however, IGF effects on enzyme maturation are less clear. To test whether IGF-I peptide administration stimulates disaccharidase activity, we administered IGF-I or the more potent analog, long [Arg3]IGF-I, at doses ranging between 2 and 12.5 micrograms g-1 d-1 to suckling Wistar rat pups by either continuous s.c. infusion or by three times daily orogastric gavage. Peptides were administered for approximately 6 d starting on d 6 or 12 postpartum with six to nine rats per group. The results of the study demonstrated that systemically but not orally administered IGF-I stimulated duodenal wet tissue weight (up to 85%) and length (up to 36%). Enzyme maturation was assessed by measuring disaccharidase biochemically in tissue homogenates. Enzyme activity was also localized histocytochemically in cryostat-sectioned duodenum. After systemic infusion of IGF-I, intestinal lactase activity increased proportional to mucosal mass in both age groups. Systemic infusion of the more potent analog, long [Arg3]IGF-I, precociously induced the decline in lactase activity and accelerated the appearance of sucrase activity in the rat pups infused during the later suckling period. These findings indicate that enzyme maturation can be accelerated by systemically derived IGF-I peptides. Orogastrically IGF-I peptides, delivered at pharmacologic doses, did not affect intestinal growth or digestive enzyme maturation in suckling rat pups treated between 6 and 18 d postpartum, indicating the efficacy of IGF-I peptides may depend on the route of delivery and postnatal age of the recipient.

Rat milk and dietary long arginine3 insulin-like growth factor I promote intestinal growth of newborn rat pups

Newborn rat pups were artificially reared by the pup in cup (PIC) method to determine whether dietary long arginine3 IGF-I (long R3 IGF-I), an IGF-I analog with high receptor affinity and low IGF binding protein (IGFBP) affinity, had efficacy on intestinal growth. IGF effects are mediated by IGFBP and receptor interactions, hence dietary-induced changes in intestinal IGF-II receptor patterns and IGFBP-3 message levels were investigated. Intestinal micrographs of pups fed rat milk replacer (RMR) for 3 d showed flattened villi with low cell counts and appeared similar to newborn intestines. Mother-fed (MF) controls and long R3 IGF-I-fed pups showed increased villi height and cell counts when compared with RMR pups, with long R3 IGF-I fed pups showing the greatest increase. At birth IGF-II-specific binding was not uniform in the intestine; specific binding was higher in the proximal intestinal section than in the distal intestinal section. However, after 3 d of MF treatment, specific binding had reversed and the distal section showed higher IGF-II-specific binding. Three days of RMR feeding did not change IGF-II-specific binding from that of the newborn pup. An IGFBP-3 message was identified in intestinal epithelium by in situ hybridization. Northern analysis of IGFBP-3 message showed a decline over time, but the change was not influenced by dietary treatments. In summary, milk-borne growth factors have the potential to affect intestinal growth within 3 d of treatment.

Increased protein synthesis after acute IGF-I or insulin infusion is localized to muscle in mice

The purpose of the present study was to determine the effect of acute administration of insulin-like growth factor I (IGF-I) or insulin on in vivo protein synthesis in muscle and other organs in fasted mice and to compare this response with that produced by feeding. Recombinant IGF-I (3.3 nmol prime, 3.33 nmol/h) or insulin (0.056 nmol/h) was infused intravenously for 60 min along with glucose to prevent hypoglycemia. Fractional rates of tissue protein synthesis (FSR) were determined by injection of [2H5]phenylalanine (25 mg/100 g body wt, 40% enriched). Both IGF-I and insulin caused a 25% increase in FSR of heart (P < 0.001) and soleus muscle (P < 0. 05) and a 65% increase in gastrocnemius and plantaris muscle (both P < 0.001), thus restoring rates to those seen in fed animals. A fivefold lower dose of IGF-I also stimulated protein synthesis in gastrocnemius muscle and heart (both P < 0.05) but not in soleus muscle. No significant effects of IGF-I on FSR were detected in liver, kidney, spleen, proximal small intestine, colon, lung, or brain. The results indicate that the ability of an overnight fast to decrease protein synthesis and the acute effects of insulin and IGF-I to stimulate protein synthesis are restricted to skeletal and cardiac muscles.

Intestinal fibroblasts regulate intestinal epithelial cell proliferation via hepatocyte growth factor

Although the presence of subepithelial intestinal fibroblasts has been well recognized, the effects of fibroblasts on intestinal epithelial cell (IEC) growth are incompletely understood. In vitro studies were undertaken to evaluate the effects of fibroblasts on the proliferation of model IEC lines. IECs (Caco-2, T84, and IEC-6) were grown alone or in the presence of human intestinal (CCD-18), lung (CCD-37), or skin explant-derived fibroblasts. Cocultures were carried out directly on irradiated fibroblasts or by Transwell coculture technique with fibroblasts and epithelial cells separated by a porous filter. Cell proliferation was assessed by [3H]thymidine incorporation and cell counts. Hepatocyte growth factor (HGF) and c-met transcript expression in IECs and fibroblasts was examined by RT-PCR and Northern blotting; protein expression was evaluated by immunoblotting. Intestinal as well as lung and skin fibroblasts substantially stimulated proliferation of Caco-2, T84, and IEC-6 cells in both direct and Transwell cocultures. In addition, fibroblast-conditioned medium stimulated IEC proliferation, suggesting a paracrine mechanism. Anti-human HGF-neutralizing antibodies blocked the growth-promoting effects in both fibroblasts and fibroblast-conditioned medium. Recombinant human HGF dose dependently promoted IEC proliferation. HGF mRNA and protein expression was restricted to fibroblasts. High levels of c-met expression were found in Caco-2 and T84 cells; in contrast, expression in fibroblasts was weak. In summary, fibroblasts stimulate IEC proliferation through a paracrine mechanism mediated predominantly by HGF.

The effect of enhanced milk yield of dairy cows by frequent milking or suckling on intake and digestibility of the diet

Groups of 9 or 10 cows were assigned to one of three treatments 1) machine-milking three times daily, 2) machine-milking six times daily, and 3) suckling three times daily in addition to machine-milking three times daily. Treatments were conducted during the first 6 wk postpartum. During wk 5, digestibility of the diet was estimated by the indigestible neutral detergent fiber method. During wk 6, milk yield and dry matter intake (DMI) were recorded daily, and plasma concentrations of glucose, nonesterified fatty acids, urea, protein, growth hormone, insulin, insulin-like growth factor I, oxytocin, and prolactin were determined. Milk yields were 38.5, 46.8, and 52.7 kg/d, and DMI were 18.1, 21.2, and 17.2, for cows on treatments 1, 2, and 3, respectively. Plasma glucose concentrations decreased, and plasma nonesterified fatty acid concentrations increased, for cows on treatments 2 and 3 compared with cows on treatment 1. Digestibility of dry matter was 57.5, 60.5, and 60.6%; of organic matter was 62.6, 64.6, and 66.8%; and of crude protein was 59.3, 62.7, and 64.6% for cows on treatments 1, 2, and 3, respectively. Concentrations of all assayed hormones, except insulin, increased moderately for cows on treatment 2 compared with cows on treatment 1 and increased dramatically for cows on treatment 3. Insulin concentrations followed the opposite trend. The DMI were positively related to milk yields and negatively related to oxytocin concentrations. Digestibility was negatively related to plasma glucose concentrations in a nonlinear pattern. The possible involvement of hormones in improvement of digestibility is discussed.

Insulin-like growth factor-I (IGF-I) stimulates regrowth of the damaged intestine in rats, when administered following, but not concurrent with, methotrexate

BACKGROUND

We tested the ability of insulin-like growth factor-I (IGF-I) to reduce damage to the intestinal mucosa (mucositis) in rats injected with methotrexate. IGF-I was infused concurrent with methotrexate administration and compared to IGF-I administered following the withdrawal of methotrexate.

METHODS

Rats were injected with methotrexate at the start of days 1, 2 and 3. IGF-I was infused for 5 days, commencing at the start of day 1 [concurrent administration] or at the start of day 4 [post-methotrexate administration].

RESULTS

IGF-I administered coincident with methotrexate failed to restore mucosal integrity to the damaged small intestine. IGF-I administered post methotrexate stimulated regrowth of the damaged intestine, particularly the ileum, with 22%, 32% and 29% increases in small intestinal weight, ileal villus height and ileal crypt depth respectively.

CONCLUSIONS

Following intestinal damage of methotrexate, IGF-I primarily induced growth of the distal small intestine. The ineffectiveness of concurrently administered IGF-I may have represented an IGF-I induced recruitment of proliferating epithelial cells to the anti-proliferative effects of methotrexate.

Effects of insulin-like growth factor-I administration on radiation enteritis in rats

BACKGROUND

Acute radiation-induced damage to the small bowel occurs frequently during abdominal radiotherapy. Since the small intestine is selectively responsive to the growth-promoting effects of insulin-like growth factor-I (IGF-I), we investigated the effects of IGF-I administration on mucosal recovery from radiation enteritis in the rat.

METHODS

Rats received a single 10-Gy dose of total abdominal irradiation followed by implantation of mini-pumps infusing either IGF-I or vehicle for 4 days. After the rats had been killed, gut organs were weighed before light microscopic and biochemical examination.

RESULTS

Irradiated rats receiving IGF-I lost less body weight than vehicle-treated rats, whereas the wet weights of the stomach, small intestine, and colon were increased by 10%, 19%, and 21%, respectively, and crypt depth was increased in the duodenum, jejunum, and ileum.

CONCLUSIONS

IGF-I administration after abdominal irradiation increased small-intestinal mass and improved indicators of mucosal integrity, suggesting acceleration of small-intestinal mucosal recovery from radiation injury.

[The therapeutic management of radiogenic oral mucositis]

BACKGROUND

Acute reactions of oral mucosa are a frequent side effect of radiotherapy, which often necessitates interruption of the treatment. Marked proliferation of tumor stem cells during treatment interruptions may occur in squamous cell carcinomata, which represent the majority of tumors in the head and neck area. Hence a fatal consequence of treatment breaks may be a significant decrease in tumor cure rates. Furthermore, marked acute responses frequently result in increased late sequelae ("consequential damage"). Therefore, amelioration of the mucosal response aiming at avoiding treatment breaks and at reduction of late reactions could definitely increase the therapeutic success of radiation treatment.

PATIENTS AND METHOD

Various possibilities for the therapeutic management of radiation-induced oral mucositis with a symptomatic or radio- and epithelial biological background are summarized and presented systematically.

RESULTS

A variety of prophylactic and therapeutic methods have been proposed for the management of acute radiation reactions of the oral mucosa. Frequently, their efficacy has been established for chemotherapy or in combination with other immunosuppressive treatments. Hence, systematical rather than local effects have to be considered.

CONCLUSIONS

In general, prophylaxis of oral mucositis is mainly based on dental restoration or edentation, in combination with frequent oral hygienic measures after the meals and with antiseptic mouthwashes. Intensive personal care is recommended. The necessity of a percutaneous endoscopic gastrostoma is dependent on the status of the patient and on size and localization of the treatment area, i.e. the impairment of food uptake which is to be expected. Therapeutic intervention is restricted to local or systemic treatment of pain and local application of antimycotics and antibiotics.

Effects of epidermal growth factor administration on repair of acetic acid-induced colonic ulcerations in rats

The effect of subcutaneous and luminal epidermal growth factor (EGF) administration on acetic acid-induced colonic ulceration was determined in adult rats. Application of acetic acid to the distal colonic lumen caused epithelial denudation, mucosal ulceration and inflammation in the exposed segment. Re-epithelialization was detectable 5 to 7 days later, with near-complete resolution of the lesion by 14 days post-injury. Luminal EGF (1.6 mg/kg bw/day) or subcutaneous EGF (200 micromilligrams/kg bw/day), administered for 4 or 6 days from the time of ulceration failed to enhance re-epithelialization of the acid-exposed segment. However, mucosal and submucosal thickening was attenuated 20-40% by subcutaneous EGF, reflecting a reduction in edema. Luminal EGF had a similar but less substantial effect in the submucosa, but was more effective at attenuating muscularis thickening adjacent to the lesion. In conclusion, administration of exogenous EGF for up to 6 days failed to enhance re-epithelialization of acetic acid-induced colonic ulcerations but did attenuate the associated edematous response.

Oral insulinlike growth factor-I stimulates intestinal enzyme maturation in newborn rats

Insulinlike growth factor-I (IGF-I) has been found in the milk of various species. To investigate if milk-borne IGF-I has any effect on postnatal gut development in neonatal animals, newborn rat pups were given orally 1 microg recombinant human IGF-I daily for 3 days. For comparison, a separate group of newborn pups was given 150 microg hydrocortisone, the hormone known to stimulate intestinal maturation in neonatal rats. Oral IGF-I treatment had no significant effect on the animal body weight nor on the weight of the stomach, small and large intestines, and pancreas. Oral administration of hydrocortisone significantly reduced body weight gain, but it had no apparent effect on internal organ weights. Both IGF-I and hydrocortisone treatments, however, significantly increased lactase, maltase and sucrase activities and hydrocortisone significantly increased aminopeptidase activity at the proximal small intestine when compared with the control. The finding supports the hypothesis that milk-borne IGF-I may play a role in regulating postnatal gut development in the suckling young.

Regulation of the mucosal epithelial barrier

Rapid re-sealing of the intestinal epithelial barrier is initially accomplished by migration of viable epithelial cells from the wound edge into the denuded area ('restitution') and only later by cell proliferation. Whereas proliferation of intestinal epithelial cells has been studied intensively, much less is known about the pivotal initial phase of cell migration. Restitution appears to be modulated by peptide growth factors/cytokines, extracellular matrix molecules, and luminally secreted products of mucus-producing cells (schematically summarized in Figure 1). Recent work has demonstrated that various cytokines (TGF-beta 1, TGF-alpha, EGF, IL-1 beta, IFN-gamma, basic FGF, KGF and HGF) present in the intestinal mucosa enhance intestinal epithelial restitution, presumably by mediating its effects through the basolateral pole of the epithelial monolayer. In addition to their effects on cell adhesion, differentiation, and spatial organization, the extracellular matrix molecules on which intestinal epithelial cells reside also have the potential to stimulate intestinal epithelial cell migration. The basement membrane components fibronectin and collagen type IV may be especially important. Finally, trefoil factors, a recently identified family of peptides which are secreted onto the luminal surface where they form the visco-elastic mucus layer through interaction with mucin glycoproteins, also promote the important process of restitution through a pathway distinct from that used by factors acting at the basolateral cell surface.