D.Grant Gall

Pathophysiology of small intestinal Malabsorption in gerbils infected with Giardia lamblia

Mongolian gerbils were infected with a human pathogenic Giardia lamblia strain and compared with sham-treated control animals 6 days after inoculation. Infection resulted in crypt hyperplasia associated with an increased enterocyte migration rate. Villus height was decreased in the duodenum, unchanged in the jejunum, and increased in the ileum of infected animals. Epithelial microvilli were markedly shortened, and brush border surface area decreased in the jejunum and ileum of infected animals. Thymidine kinase activity was increased in isolated duodenal villus enterocytes but did not differ in the jejunum and ileum. In vitro and in vivo experiments showed that the infection resulted in decreased jejunal glucose-stimulated electrolyte, water, and 3-O-methyl-D-glucose absorption, whereas in the ileum in vitro electrolyte and 3-O-methyl-D-glucose absorption was similar in infected and control animals. Thus, in the jejunum infection causes electrolyte, solute, and fluid malabsorption associated with decreased brush border surface area. The results indicate that the diarrhea associated with giardiasis is caused by malabsorption rather than active secretion.

Structural and functional adaptation following jejunal resection in rabbits: Effect of epidermal growth factor

BACKGROUND/AIMSnRemnant small intestine undergoes adaptation following massive resection. The aim of this study was to examine the effect of epidermal growth factor (EGF) on ileal adaptation following proximal resection.nnnMETHODSnNew Zealand white rabbits, aged 8 weeks, underwent 2/3 proximal resection, and ileal mucosal adaptation was assessed 10 and 21 days postsurgery. In a second series of experiments, animals with resection received oral EGF (40 micrograms.kg-1.day-1) for 5 days, and the effect on adaptation was assessed 10 days postsurgery.nnnRESULTSnTransection alone stimulated mucosal hyperplasia, intestinal sucrase specific activity, and glucose transport at 10 days but not at 21 days. Resection resulted in mucosal hyperplasia at both time periods and increased disaccharidase specific activity at 10 days postresection. In contrast, 3 O-methyl-D-glucose transport was significantly decreased compared with both groups at both time periods. EGF treatment in animals with resection did not alter mucosal proliferation but did stimulate maltase specific activity and caused a 3-4-fold increase in glucose transport and phlorizin binding.nnnCONCLUSIONSnFollowing proximal resection, adaptation of intestinal digestive and absorptive function does not parallel mucosal hyperplasia. Administration of EGF to resected animals enhances glucose absorption and may have a therapeutic role in the management of short gut syndrome.

Transport abnormalities during intestinal anaphylaxis in the rat: Effect of antiallergic agents☆☆☆★

Our previous studies demonstrated that rats sensitized to egg albumin had reduced intestinal absorption of water and electrolytes in response to intraluminal antigen. The rapid onset of this effect and reduction in mucosal histamine and numbers of granulated mast cells in the lamina propria suggested a reaginic (IgE) mechanism involving mast cell mediators. In this study we examined the effect of antiallergic agents on the intestinal transport abnormalities in our model. Sensitized rats, 14 days after intraperitoneal injection of 10 micrograms of egg albumin plus alum had specific IgE serum titers greater than or equal to 1:64; control rats had no measurable IgE antibodies. Net fluxes of Na+, Cl-, and H2O were determined by in vivo perfusion during a 1-hour antigen-free period and then a 1-hour antigen period. Sodium cromoglycate, administered intravenously (20 mg/kg) or in the perfusate (5 X 10(-4) mol/L) failed to prevent mucosal mast cell degranulation as evidenced by histamine release or the decrease in absorption of H2O, Na+, and Cl- induced by antigen exposure. In contrast, 10(-3) mol/L of doxantrazole in the perfusate completely inhibited these changes. Histamine receptor antagonists, H1, diphenhydramine, or H2, cimetidine, in perfusates had no effect on the transport abnormalities. Our findings support a role for intestinal mucosal mast cells, but not connective tissue mast cells, in the pathogenesis of the intestinal dysfunction associated with mucosal IgE-mediated reactions to food proteins and suggest that mast cell mediators other than histamine are involved.

Intestinal permeability and postheparin plasma diamine oxidase activity in the prediction of Crohn's disease relapse

A method of detecting presymptomatic relapse of Crohns disease could allow for the selective use of maintenance or intensified medical therapy in those with an increased risk of relapse. The aim of this study was to evaluate three potential laboratory markers of relapse: intestinal and gastroduodenal permeability and plasma diamine oxidase activity. Intestinal permeability (lactulose/mannitol test), gastroduodenal permeability (urinary sucrose excretion), and postheparin plasma diamine oxidase activity were serially measured in 61 adults with Crohns disease in remission (CDAI <150) for at least 30 days. Subjects were followed periodically for clinical relapse (CDAI >150 and increased by at least 100 points or the need for steroids or surgery). Fourteen patients (23%) relapsed. A cut-off of 0.030 for the lactulose/mannitol ratio was defined. Those with ratios above the cutoff had a 7.0 times greater risk of relapse (p<0.001). Three subjects who went from a normal ratio to an abnormal ratio relapsed, whereas none of 32 subjects with a repeatedly normal ratio relapsed. Sucrose excretion and plasma diamine oxidase activity did not predict relapse. Serial testing of intestinal permeability, but not of gastroduodenal permeability or plasma diamine oxidase activity, was useful in predicting relapse in asymptomatic patients.

Rat jejunal mucosal response to histamine and anti-histaminesin vitro. Comparison with antigen-induced changes during intestinal anaphylaxis

We previously showed that rats sensitized to egg albumin (EA) respond toin vivo intraluminal antigen-challenge with decreased net absorption of water and electrolytes and depletion of mucosal histamine. However, administration of anti-histamines did not prevent the transport abnormalities. The presentin vitro studies examined the effect of histamine to alter net ion transport and the ability of diphenhydramine (DPH) and cimetidine (CIM) to block the responses to both histamine and antigen. Control rat jejunum was mounted in Ussing chambers and histamine was added to the serosal side either in the absence or presence of DPH or CIM. In control tissues histamine caused a transient increase in short-circuit current (Isc) in a dose-dependent manner between 10−5 and 10−4 M which was blocked by 10−5 M DPH but was unaffected by CIM in concentrations up to 10−4 M. There was no response to EA. Jejunum from sensitized rats exposed to EA demonstrated a biphasic Isc response: a rapid transient rise followed by a somewhat less elevated but sustained component. In tissues pre-treated with DPH the initial peak Isc response was significantly reduced. In the presence of the neurotoxin, tetrodotoxin, the initial peak was unaffected but the sustained component was reduced. Our results indicate that H1-receptors mediated the effects of histamine in rat jejunal mucosa but that during intestinal anaphylaxis histamine is responsible for only a portion of the antigen-induced transport abnormalities. Our data also suggest that IgE-mediated reactions in the intestine may involve an interaction between mast cell mediators and enteric nerves.

Intestinal anaphylaxis in the rat: Mediators responsible for the ion transport abnormalities

Antigen challenge of jejunal epithelium from rats sensitized to egg albumin induces an active Cl− secretory process secondary to release of mucosal mast cell mediators. The present study was designed to define the relative role of these mast cell mediators and the enteric nervous system in the transport abnormalities associated with intestinal anaphylaxis. Net ion transport of stripped jejural tissue from sensitized and sham-treated animals was studied in Ussing chambers. The Cl− secretory response induced by egg albumin during intestinal anaphylaxis was similar to that after addition of 5-hydroxytryptamine (5-HT), histamine, and prostaglandins D2 and E2 to jejunal tissue. Cinanserin, a 5-HT2-receptor antagonist, virtually abolished the response to 5-HT and totally abolished the response to egg albumin. Methysergide, a 5-HT1-receptor antagonist had no effect on either response. Indomethacin, an inhibitor of prostaglandin synthesis, significantly inhibited the 5-HT and egg albumin response. Diphenhydramine, an H1-receptor antagonist and cimetidine, an H2-receptor antagonist both significantly inhibited the histamine response but neither altered the response to egg albumin. Atropine, an anticholinergic, and tetrodotoxin, a nerve blocker, did not inhibit the antigen induced anaphylactic response. These results indicate that 5-HT, acting through 5-HT2 receptors is largely responsible for the transport abnormalities seen in intestinal anaphylaxis induced by egg albumin while prostaglandins appear to play a partial role. The findings do not support a role for the enteric nervous system for the egg albumin induced changes in Cl− secretion.

Postnatal development of hepatic bile formation in the rabbit

To investigate postnatal maturation of hepatic bile formation, bile output was measured in four groups of rabbits: suckling infants at ages 10–14, 18–22, and 26–30 days, and adults. Bile output was collected directly from the common duct during three 1-hr periods: a basal period followed by intravenous infusion of 1 and then 2 μmol/min/kg of glycodeoxycholic acid. [14C]Erythritol and [3H]inulin clearances measured canalicular bile flow and biliary permeability. Under basal conditions and with the exogenous bile acid, bile flow and bile salt secretion were lowest in 10-to 14-day-old infants and showed a gradual increase with increasing age. Bile salt-dependent flow, the linear increase in flow relative to bile salt secretion, was higher in the 10-to 14-and 17-to 22-day-old compared to the adult and 25-to 30-day-old groups. The ratio of chloride to bile salt secreted was also higher in the two younger groups. Bile salt-independent flow at theoretical zero bile salt secretion was absent in the younger groups, but evident in the adult and 25-to 30-day-old rabbits. Canalicular flow estimated by erythritol clearance was linearly related to bile salt secretion. Inulin clearance relative to erythritol clearance was higher in the 10-to 14-day-old infants than the adults. Thus, bile flow and bile salt secretion are reduced in the young infant but rise to near adult levels at the time of weaning, 25–30 days in the rabbit. The increase in flow results from increased bile salt secretion and the appearance of bile salt-independent flow. Biliary permeability as measured by inulin clearance is increased in the young, allowing increased water and electrolyte movement per unit of bile salt to maintain bile flow despite a depressed bile salt secretion rate.

Distribution and function of brain natriuretic peptide in the stomach and small intestine of the rat

The distribution and function of brain natriuretic peptide (BNP) was studied in the rat stomach and jejunum. BNP-like immunoreactive nerves were found in the myenteric plexus, circular muscle, submucosa and in the crypt region of the jejunum. In the stomach, BNP-like immunoreactivity was found in the myenteric plexus, circular muscle, submucosa and at the base of the gastric glands. In the submucosa, BNP-like immunoreactivity was often associated with blood vessels. In segments of rat jejunum mounted in Ussing chambers, serosal exposure to rat BNP caused a concentration-dependent increase in short circuit current. A maximal effect of 18 +/- 4 microA/cm2 was observed with 1 microM BNP. The effect was quantitatively and qualitatively similar to that elicited by serosal exposure to equimolar atrial natriuretic peptide. The response to BNP was reduced by 88% in chloride free Krebs buffer, by 83% in tissues pretreated with cinanserin, an antagonist of the 5-HT2 subtype of the 5-hydroxytryptamine receptor, and by 96% in tissues pretreated with tetrodotoxin, a blocker of axonal conduction. These results are consistent with a physiological role for BNP as a neuromodulator of gastrointestinal electrolyte transport.

Rat gastric motor response to food protein-induced anaphylaxis

BACKGROUND/AIMSnAntigen challenge of sensitized rats leads to delayed gastric emptying, but the mechanism (gastroparesis or prolonged trituration) and mediators are unknown.nnnMETHODSnHooded Lister rats were sensitized by intraperitoneal injection of egg albumin as antigen, and control rats were sham-sensitized. On day 14, antral manometric and antroduodenal myoelectric activities in sensitized and sham-sensitized rats were recorded in response to antigen challenge, and the contractility of gastric antral circular muscle strips (mucosa intact) in standard tissue baths was measured in response to antigen or other agents.nnnRESULTSnIn vivo, the intragastric antigen challenge of sensitized (but not sham-sensitized) rats provoked diarrhea, reduction in the antral motility index, and disruption of the duodenal migrating motor complex. In vitro, antigen induced a tonic contraction of antral circular muscle segments from sensitized animals. Doxantrazole, but not disodium cromoglycate, inhibited antigen-induced contraction. Whereas histamine, 5-hydroxytryptamine, prostaglandins, leukotrienes, and platelet-activating factor contracted gastric muscle strips, neither specific antagonists, prostaglandin synthase, or 5-lipoxygenase inhibitors inhibited antigen-induced contraction. Tetrodotoxin increased antigen-induced contraction; however, the antigen-induced contraction was unaffected by atropine, guanethidine, or NG-nitro-L-arginine methyl ester.nnnCONCLUSIONSnFood protein-induced, immunoglobulin E-mediated delayed gastric emptying in sensitized rats is associated with a transient reduction in gastric antral contractions. Antigen-induced contraction appears to be under nonadrenergic, noncholinergic, nonnitroxinergic inhibitory neural control.

The role of the epidermal growth factor receptor in microbial infections of the gastrointestinal tract

The epidermal growth factor receptor (EGFr) is a transmembrane glycoprotein with an intrinsic tyrosine kinase. Ligand-binding to the EGFr activates cell signaling, phosphorylates protein kinases, and rearranges cytoskeletal proteins - responses that resemble those induced by microbial attachment to cell surfaces, a process known to be mediated by host cell receptors in a number of cases. This article critically reviews the possible role played by the EGFr in microbial colonization, and discusses how modulation of the EGF-EGFr axis may affect infection of the gastrointestinal tract.