Pituitary hormones and the small bowel: effect of hypophysectomy on intestinal adaptation to small bowel resection in the rat

Intestinal adaptation and rehabilitation

Massive intestinal resection is a regrettably necessary but life-saving intervention for progressive or fulminant necrotizing enterocolitis (NEC). However, the resultant short bowel syndrome (SBS) poses its own array of challenges and complications. Within hours of such an abrupt loss of intestinal length, the intestine begins to adapt. Our ability to understand this process of intestinal adaptation has proven critical in our ability to clinically treat the challenging problem of short bowel syndrome. This review first highlights key data relating to intestinal adaptation including structural and functional changes, biochemical regulation, and other factors affecting the magnitude of intestinal adaptation responses. We then focus on intestinal rehabilitation as it relates to strategies to enhance intestinal adaptation while meeting nutritional needs and preventing complications of parenteral nutrition.

Pancreas-Brain Crosstalk

The neural regulation of glucose homeostasis in normal and challenged conditions involves the modulation of pancreatic islet-cell function. Compromising the pancreas innervation causes islet autoimmunity in type 1 diabetes and islet cell dysfunction in type 2 diabetes. However, despite the richly innervated nature of the pancreas, islet innervation remains ill-defined. Here, we review the neuroanatomical and humoral basis of the cross-talk between the endocrine pancreas and autonomic and sensory neurons. Identifying the neurocircuitry and neurochemistry of the neuro-insular network would provide clues to neuromodulation-based approaches for the prevention and treatment of diabetes and obesity.

Intestinal adaptation following resection

Intestinal adaptation is a natural compensatory process that occurs following extensive intestinal resection, whereby structural and functional changes in the intestine improve nutrient and fluid absorption in the remnant bowel. In animal studies, postresection structural adaptations include bowel lengthening and thickening and increases in villus height and crypt depth. Functional changes include increased nutrient transporter expression, accelerated crypt cell differentiation, and slowed transit time. In adult humans, data regarding adaptive changes are sparse, and the mechanisms underlying intestinal adaptation remain to be fully elucidated. Several factors influence the degree of intestinal adaptation that occurs post resection, including site and extent of resection, luminal stimulation with enteral nutrients, and intestinotrophic factors. Two intestinotrophic growth factors, the glucagon-like peptide 2 analog teduglutide and recombinant growth hormone (somatropin), are now approved for clinical use in patients with short bowel syndrome (SBS). Both agents enhance fluid absorption and decrease requirements for parenteral nutrition (PN) and/or intravenous fluid. Intestinal adaptation has been thought to be limited to the first 1-2 years following resection in humans. However, recent data suggest that a significant proportion of adult patients with SBS can achieve enteral autonomy, even after many years of PN dependence, particularly with trophic stimulation.

Effect of recombinant human growth hormone on intestinal absorption and body composition in children with short bowel syndrome

This prospective study aimed to establish the effect of recombinant human growth hormone (rhGH) on intestinal function in children with short bowel syndrome (SBS). Eight children with neonatal SBS were included. All were dependent on parenteral nutrition (PN) for >3 years (range, 3.8-11.6 years), with PN providing >50% of recommended dietary allowance for age (range, 50%-65%). The subjects received rhGH (Humatrope) 0.13 mg/kg/d subcutaneously over a 12-week period. The follow-up was continued over a 12-month period after rhGH discontinuation. Clinical and biological assessments were performed at baseline, at the end of the treatment period, and 12 months after the end of treatment. No side effects related to rhGH were observed. PN requirements were decreased in all children during the course of rhGH treatment. Between baseline and the end of treatment, significant increases were observed in concentrations (mean ± standard deviation) of serum insulin-like growth factor 1 (103.1 ± 49.9 µg/L vs 153.5 ± 82.2 µg/L; P < .01), serum insulin-like growth factor-binding protein 3 (1.7 ± 0.6 mg/L vs 2.5 ± 0.9 mg/L; P < .001), and plasma citrulline (16.5 ± 14.8 µmol/L vs 25.2 ± 18.3 µmol/L; P < .05). A median 54% increase in enteral intake (range, 10%-244%) was observed (P < .001) and net energy balance improved significantly (P < .002). It was necessary for 6 children to be maintained on PN or restarted after discontinuation of rhGH treatment, and they remained on PN until the end of the follow-up period. A 12-week high-dose rhGH treatment allowed patients to decrease PN, but only 2 patients could be definitively weaned from PN. Indications and cost-effectiveness of rhGH treatment for SBS pediatric patients need further evaluation.

Morphological, kinetic, membrane biochemical and genetic aspects of intestinal enteroplasticity

The process of intestinal adaptation (“enteroplasticity”) is complex and multifaceted. Although a number of trophic nutrients and non-nutritive factors have been identified in animal studies, successful, reproducible clinical trials in humans are awaited. Understanding mechanisms underlying this adaptive process may direct research toward strategies that maximize intestinal function and impart a true clinical benefit to patients with short bowel syndrome, or to persons in whom nutrient absorption needs to be maximized. In this review, we consider the morphological, kinetic and membrane biochemical aspects of enteroplasticity, focus on the importance of nutritional factors, provide an overview of the many hormones that may alter the adaptive process, and consider some of the possible molecular profiles. While most of the data is derived from rodent studies, wherever possible, the results of human studies of intestinal enteroplasticity are provided.

Intestinal mucosal adaptation

Intestinal failure is a condition characterized by malnutrition and/or dehydration as a result of the inadequate digestion and absorption of nutrients. The most common cause of intestinal failure is short bowel syndrome, which occurs when the functional gut mass is reduced below the level necessary for adequate nutrient and water absorption. This condition may be congenital, or may be acquired as a result of a massive resection of the small bowel. Following resection, the intestine is capable of adaptation in response to enteral nutrients as well as other trophic stimuli. Identifying factors that may enhance the process of intestinal adaptation is an exciting area of research with important potential clinical applications.

Haplotype insufficiency for suppressor of cytokine signaling-2 enhances intestinal growth and promotes polyp formation in growth hormone-transgenic mice

GH may improve intestinal growth or function in patients with short bowel syndrome. Excessive trophic effects of GH or IGF-I may contribute to neoplastic growth or increased colorectal cancer risk in acromegaly. Identification of mechanisms that limit the tumorigenic potential of GH and IGF-I is desirable. Suppressor of cytokine signaling-2 (SOCS2) limits GH action on body and organ growth, but its role in GH action on intestine is unknown. We tested the hypothesis that SOCS2 limits GH-induced intestinal growth or neoplasia in vivo. GH-transgenic (GH-TG) mice were crossed with SOCS2 null mice to generate wild-type (WT) or transgenic (TG) mice with zero (HO-WT; HO-TG), one (HT-WT; HT-TG), or two (WT-WT; WT-TG) functional SOCS2 genes. No HO-TG mice were derived from crossbreeding. WT-WT, HT-WT, WT-TG, and HT-TG were compared. Body weight, small intestine and colon growth, and levels of jejunal IGF-I and sucrase-isomaltase mRNAs were assessed. Colon was analyzed for abnormal lesions. HT-WT did not differ from WT-WT. Compared with WT-TG, HT-TG had significantly increased body weight, small intestine growth, and local IGF-I expression and decreased sucrase-isomaltase expression. HT-TG colon spontaneously developed multiple hyperplastic and lymphoid polyps. GH-induced activation of STAT5 DNA binding activity was enhanced in intestine of SOCS2 null mice compared with WT control. Haplotype insufficiency for SOCS2 promotes trophic actions of GH in small intestine and promotes preneoplastic growth in colon during excess GH. Small variations in SOCS2 expression levels may significantly influence the outcome of therapeutic GH or acromegaly in intestine.

[Example of safety measures for antineoplastic agents immediately after market launch--a case of TS-1 capsule all example use result investigation that executes safety monitoring--]

As a measure to ensure safe use of TS-1 during the early marketing period, a drug use investigation was conducted on an all-case basis. Extra safety monitoring,rarely included in the use investigation,was also planned for patients who began therapy with this agent. Of the 4,177 subjects registered during the year beginning in March 1999, 3,882 started TS-1 therapy. Aside from 74 dropouts, 3,808 cases were evaluable for safety. The overall incidence of adverse reactions, with high frequencies of myelosuppression and gastrointestinal disorders, was 74.3%: a result similar to an incidence of 77.5% (100/129) found in the early phase II trial with gastric cancer patients. Safety monitoring made it possible to check if a given patients was eligible for proper use before treatment is begun. During TS-1 administration,collaboration was formed between physicians and medical representatives to ensure regular laboratory testing and to check the test findings. Measures were considered necessary to secure the safe use of drugs with manifest risk of serious adverse reactions, such as antineoplastic agents, during the initial period of market introduction. Our present approach proved effective as one of such measures.

Irreversible intestinal failure

Intestinal failure (IF) can be defined as the reduction of functional gut mass below the minimal amount necessary for digestion and absorption adequate to satisfy the nutrient and fluid requirements for maintenance in adults or growth in children. In developed countries, IF mainly includes individuals with the congenital or early onset of conditions requiring protracted or indefinite parenteral nutrition (PN). Short bowel syndrome was the first commonly recognized cause of protracted IF. The normal physiologic process of intestinal adaptation after extensive resection usually allows for recovery of sufficient intestinal function within weeks to months. During this time, patients can be sustained on parenteral nutrition. Only a few children have permanent intestinal insufficiency and life-long dependency on PN. Non-transplant surgery including small bowel tapering and lengthening may allow weaning from PN in some cases. Hormonal therapy with recombinant human growth hormone has produced poor results while therapy with glucagon-like peptide-2 holds promise. Congenital diseases of enterocyte development such as microvillus inclusion disease or intestinal epithelial dysplasia cause permanent IF for which no curative medical treatment is currently available. Severe and extensive motility disorders such as total or subtotal intestinal aganglionosis (long segment Hirschsprung disease) or chronic intestinal pseudo-obstruction syndrome may also cause permanent IF. PN and home-PN remain are the mainstays of therapy regardless of the cause of IF. Some patients develop complications while receiving long-term PN for IF especially catheter related complications (thrombosis, sepsis) and liver disease. These patients may be candidates for intestinal transplantation. This review discusses the causes of irreversible IF and emphasizes the specific medico-surgical strategies for prevention and treatment of these conditions at several stages of IF.

Adaptation following intestinal resection: mechanisms and signals

The intestine has an inherent ability to adapt morphologically and functionally in response to internal and external environmental changes. The functional adaptations encompass modifications of the brush border membrane fluidity and permeability, as well as up- or down-regulation of carrier-mediated transport. Intestinal adaptation improves the nutritional status following the loss of a major portion of the small intestine, following chronic ingestion of ethanol, following sublethal doses of abdominal irradiation, in diabetes, in pregnancy and lactation, with ageing, and with fasting and malnutrition. Following intestinal resection, morphological and functional changes occur depending upon the extent of the intestine removed, the site studied, and the lipid content of the diet. Therefore, intestinal adaptation has important implications in the survival potential and welfare of the host. An understanding of the mechanisms of, and signals for, intestinal adaptation in the experimental setting forms the basis for the use of management strategies in humans with the short-bowel syndrome.

Glutamine enhances the gut-trophic effect of growth hormone in rat after massive small bowel resection

Background. Bowel-specific nutrient, glutamine, growth hormone, and modified diet have been reported to jointly improve nutrient absorption in patients with short bowel syndrome. However, controversy exists about the exact treatment factor. In this study we attempted to analyze the individual and combined effect of glutamine supplementation and growth hormone on small bowel adaptation by using tube feeding to control luminal nutrition supply. Materials and methods. Thirty-two adult male Sprague-Dawley rats (278 +/- 8 g) underwent 85% mid-small bowel resection and were randomly assigned to four groups: Control, receiving control liquid diet via a gastrotomy tube; GLN, receiving liquid diet enriched with 20 g. L(-1) glutamine; GH, receiving subcutaneous growth hormone (GH) (0.3 IU, bid); and GLN + GH, receiving both glutamine supplementation and GH treatment. All animals were provided with isocaloric (60 kcal/day) and isonitrogenous (0.686 g/day) nutrition. Absorption tests were performed in the form of oral nutrient tests with (14)C-labeled glucose and (3)H-labeled palmitic acid on the Postoperative Day 12. Results. GH treatment significantly increased the plasma insulin-like growth factor I (IGF-I) level, body weight, jejunal and ileal villous height and mucosal thickness, and peak plasma (14)C and (3)H levels. Glutamine supplementation did not produce a significant difference; however, combined with GH treatment, glutamine supplementation further increased body weight, plasma IGF-I level, jejunal and ileal villous height and mucosal thickness, and peak plasma (14)C and (3)H levels significantly. Conclusions. After massive small bowel resection, enteral glutamine supplementation alone has no remarkable beneficial effect on bowel adaptation. However, glutamine supplementation enhanced the gut-trophic effect of GH.

The effectiveness of growth hormone, glutamine and a low-fat diet containing high-carbohydrate on the enhancement of the function of remnant intestine among patients with short bowel syndrome: a review of published trials

Many patients who undergo extensive resection of the gastrointestinal tract develop malabsorption which, in the worst cases, requires long-term parenteral nutrition at home, frequently on a permanent basis. Such patients can be defined as having intestinal failure resulting from the short bowel syndrome. In 1995, Wilmore's group hypothesized that the administration of growth factors and nutrients could enhance further adaptation of the remnant intestine and thereby improve absorption. The demonstrated, through controlled clinical trials, the benefit of such treatment among 47 adults with less than 200 cm of small intestine. Over the past few years, similar trials as well as animal experiments have been conducted by the same authors and other groups with conflicting results. We have performed a systematic search on the electronic databases for the purpose of identifying the evidence published so far on this subject. Our analysis suggests that the benefit of administering recombinant human growth hormone alone, or together with glutamine with or without a low-fat diet containing high-carbohydrate (fibre) is, if any, marginal.

Enhanced survival and mucosal repair after dextran sodium sulfate-induced colitis in transgenic mice that overexpress growth hormone

BACKGROUND & AIMS

Growth hormone (GH) is used as therapy for inflammatory bowel disease (IBD), but the specific effects on intestine are unknown. Transgenic mice overexpressing GH (MT1-bGH-TG) were used to test whether increased plasma GH levels alter inflammation or crypt damage during dextran sodium sulfate (DSS)-induced colitis.

METHODS

MT1-bGH-TG and wild-type (WT) littermates were given 3% DSS for 5 days followed by up to 10 days of recovery. Colitis and epithelial cell proliferation were evaluated histologically. Plasma insulin-like growth factor (IGF)-I and colonic IGF-I, interleukin (IL)-1beta, and intestinal trefoil factor (ITF) messenger RNAs (mRNAs) were measured.

RESULTS

DSS induced similar disease onset in MT1-bGH-TG and WT. More MT1-bGH-TG survived than WT. By recovery day 7, MT1-bGH-TG had less inflammation and crypt damage, elevated plasma IGF-I, and increased colonic ITF expression relative to WT. Colonic IL-1beta was elevated in DSS-treated MT1-bGH-TG and WT, but IL-1beta mRNA abundance correlated with disease only in WT. MT1-bGH-TG showed earlier increases in epithelial cell proliferation than WT during recovery but only WT showed atypical repair.

CONCLUSIONS

GH does not alter susceptibility to acute DSS-induced colitis but enhances survival, remission of inflammation, and mucosal repair during recovery. GH therapy may be beneficial during active IBD by improving mucosal repair.

Intestinal transplantation

Intestinal transplantation might become the alternative to definitive parenteral nutrition in patients with permanent intestinal failure. Indeed, recent advances in immunosuppressive treatment and better monitoring and control of acute rejection have brought intestinal transplantation into the realms of standard treatment of intestinal failure. This procedure may be performed in adult or paediatric patients under certain conditions. This short review focuses on the current clinical results and indications for intestinal transplantation and discusses the strategy regarding this challenging procedure.

Molecular basis of intestinal adaptation: the role of the insulin-like growth factor system

Ongoing and future approaches to the cellular and molecular actions of insulin-like growth factor I (IGF-I) and growth hormone (GH) in intestinal adaptation are reviewed. This is highly relevant to understanding the benefits and risks associated with increasing use of GH and IGF-I in patients with short bowel syndrome or other bowel diseases. As other growth factors share some of the properties of IGF-I including local expression in bowel, activation of signaling pathways common to other growth factors or cytokines, and modulation of action by growth factor-binding proteins or secreted receptor isoforms. The general issues and approaches outlined for IGF-I should, therefore, serve as a model for studies aimed at understanding the cellular and molecular mechanisms of action of other growth factors that are implicated in intestinal adaptation.

Short bowel syndrome in pediatric patients

The treatment of infants and children with short bowel syndrome aims at restoring the intestinal continuity and at improving the physiological process of gut adaptation. Mucosal hyperplasia allows the remaining gut to ensure an adequate digestion and an absorption process leading to intestinal autonomy. During the period of adaptation, appropriate parenteral and/or enteral feeding must be directed at maintaining an optimal nutritional status. Delay of intestinal autonomy depends on the characteristics of the residual intestine: length, presence of the ileocecal valve and colon, and motor function. Bacterial overgrowth compromises intestinal adaptation and increases the risk of liver disorders. Few patients will remain long-term dependent on parenteral nutrition. All approaches aimed at achieving intestinal autonomy should be tried: use of trophic factors, intestinal tapering, and lengthening. In a few residual patients, permanent intestinal failure or extreme short bowel syndrome require intestinal transplantation.

Effect of hypophysectomy on endocrine cell types in rat gastrointestinal mucosa

The effect of hypophysectomy on the gastrointestinal tract was studied in the rat 8 wk after operation, particularly regarding the frequency and distribution of serotonin, somatostatin and gastrin-immunoreactive cells. Body weight, the length of the intestine and the thickness of the mucosa of the antrum and small intestine were all reduced in the hypophysectomised rats compared with sham-operated and untreated controls. In the hypophysectomised animals the serotonin-immunoreactive cells were fewer in the antrum and caecum, whereas they were more numerous in the proximal large intestine. There were fewer gastrin-immunoreactive cells in the antrum, while the somatostatin-immunoreactive cells were more numerous in the antrum and caecum. The significant influence of hypophysectomy on the gastrointestinal tract could be direct, but could also be associated with the marked effect of pituitary deficiency on endocrine cells, known to exert both trophic and antitrophic actions. However, it could also be an indirect effect on metabolism, resulting in lower food intake, other endocrine cell systems, and growth factors.

Enhanced growth of small bowel in transgenic mice overexpressing bovine growth hormone

BACKGROUND

Transgenic mice with a bovine growth hormone gene linked to a mouse metallothionein I promoter (growth hormone transgenics) are a model of chronic growth hormone excess.

METHODS

Growth of small bowel mucosa in ad libitum-fed growth hormone transgenics and wild type littermates and in growth hormone transgenics pair fed with wild-type littermates were compared.

RESULTS

In both groups, body weight and small bowel weight were greater in growth hormone transgenics. Similarly, mucosal mass was 50%-100% greater in growth hormone transgenics, and the effect was greatest in proximal bowel. Villus height, measured in jejunum, was also greater in growth hormone transgenics. Measurements of mucosal proliferation did not differ between the growth hormone transgenics and wild type. Abundance of insulin-like growth factor-I messenger RNA in bowel was greater in growth hormone transgenics.

CONCLUSIONS

Chronic growth hormone excess results in increased growth of small bowel mucosa. This effect appears to be specific because it occurred in ad libitum-fed and diet-restricted growth hormone transgenics, influenced villus height, and was more pronounced in upper than lower small bowel. The effect of chronic growth hormone excess does not appear to be secondary to an increase in the rate of mucosal proliferation, suggesting an effect on lifespan of mucosal cells.

Effects of bolus doses of fat on small intestinal structure and on release of gastrin, cholecystokinin, peptide tyrosine-tyrosine, and enteroglucagon

To investigate the enterotrophic effects of bolus doses of long chain triglycerides, two groups of eight female Wistar rats were fed identical diets with 48.2% total calories as the essential fatty acid rich oil Efamol. To one group the oil was given in twice daily bolus doses by gavage, while for the other group the oil was mixed with the remainder of the feed and thus consumed over 24 hours. The animals were killed after 20 to 22 days. Bolus dosing significantly increased parameters of mucosal mass along the length of the small intestine in association with an increase in two hour accumulation of vincristine arrested metaphases in small intestinal crypts. In a second experiment, four replicate studies were carried out, each involving two groups of 12 rats respectively fed as described above. After 21 days one animal from each group was killed every two hours, providing regular plasma samples over 24 hours for measurement of gastrin, cholecystokinin, peptide tyrosine-tyrosine and enteroglucagon. Bolus dosing markedly enhanced release of peptide tyrosine-tyrosine and enteroglucagon, but not of gastrin or cholecystokinin. Thus, the enhanced enterotrophic effects of bolus doses of long chain triglycerides could be mediated by release of a distally located gut peptide, perhaps enteroglucagon.

Simultaneous measurement of intestinal crypt cell production rate and water absorption

Intestinal cell proliferation and cell production is best quantified by measuring the rate of accumulation of vincristine arrested metaphases in microdissected intestinal crypts to determine the crypt cell production rate (CCPR). Studies of intestinal adaptation could be much more informative if a valid measure of intestinal function could also be included. One such method is the water absorption capacity. The CCPR of the jejunum and intestinal water absorption were measured in 19 groups of hypo and hyperproliferative rats which were in a 'steady state' of cell production and turnover. The minimum values were obtained after hypophysectomy and the maximum values were observed in lactation. Crypt cell production rate and absorption were significantly correlated (p less than 0.001) to each other. There was a significant (p less than 0.001) correlation between both CCPR and absorption and dry weight of the intestinal segment studies and food intake. Body weight was a poor predictor of either CCPR or absorption. The combined study of CCPR and water absorption is thus a practical and convenient approach to the study of intestinal cell proliferation and intestinal adaptation.

Effect of diverting bile and pancreatic secretions into the ileum on small bowel mucosa in rats fed a liquid formula diet

The long-term effects of diverting bile and pancreatic secretions directly into the ileum on small bowel mucosa was determined in rats fed a hydrolyzed liquid formula diet. Male Sprague-Dawley rats were divided into four experimental groups: duodenal papilla transplant-sham operation, transplantation of the duodenal papilla into the ileum, bile duct sham operation, and transplantation of the bile duct into the ileum. After 28 days, animals were killed, the same bowel removed, rinsed with cold isotonic saline, and divided into six segments (two jejunal segments and four ileal segments). The mucosa of each segment was weighed and assayed for DNA and protein concentration, and specific activity of sucrase and maltase. Bile and particularly pancreatic secretions diverted into the ileum stimulated local mucosal growth compared with their respective controls. The absence of pancreatic secretions from the jejunum also was associated with an increase in jejunal mucosal mass. Diverting pancreatic secretions into the ileum decreased ileal sucrase and maltase specific activity while the absence of both bile and pancreatic secretions from the jejunum increased jejunal sucrase specific activity. The results suggest that bile and pancreatic secretions entering the ileum are important factors in stimulating ileal mucosal hyperplasia while the absence of these secretions from the proximal intestine is associated with greater jejunal mucosal growth. The mechanisms regulating jejunal mucosal growth appear to be different than those influencing the ileum.

Effects of octapeptide-cholecystokinin, secretin, and glucagon on intestinal mucosal growth in parenterally nourished rats

Nutrients in the lumen of the small intestine may cause the release of enteric hormones which directly or indirectly stimulate intestinal mucosal growth. Male Sprague-Dawley rats with either an intact small bowel or following jejunal resection were maintained on total parenteral nutrition (TPN). C-terminal octapeptide-cholecystokinin alone or combined with secretin, or glucagon alone were added to the intravenous nutrient solution and continuously infused. Control rats received only TPN or gastric infusion of isocaloric amounts of TPN solution. After 7 days, intestinal hypoplasia was noted in rats with an intact bowel maintained on TPN alone compared with the gastrically infused group. TPN did not maintain the proximal-distal gradient of mucosal mass. Continuous intravenous infusion of octapeptide-cholecystokinin alone and together with secretin in rats maintained on TPN significantly stimulated small bowel mucosal growth, partially restoring the proximal-distal gradient. Glucagon infusion did not stimulate mucosal growth. Rats with a jejunal resection and maintained on TPN for 7 or 14 days failed to develop mucosal hyperplasia of the ileum in contrast to rats given the TPN solution intragastrically. Continuous intravenous infusion of octapeptide-cholecystokinin in rats maintained on TPN after jejunal resection caused significant mucosal growth in the ileum compared with the rats maintained on TPN alone, but not to the extent seen in gastrically fed animals. Intravenous infusion of octapeptide-cholecystokinin stimulates small-bowel mucosal growth. Secretin appears to have an additional effect when given together with octapeptide-CCK. Although a direct trophic action by these hormones on the intestinal mucosa is possible, this effect is more likely mediated via stimulation of pancreaticobiliary secretions.