Gilbert A. Castro

Structural and hormonal alterations in the gastrointestinal tract of parenterally fed rats

This study examines the effect of prolonged absence of oral food intake on structural parameters of the gastrointestinal tract in rats maintained nutritionally by intravenous feeding for up to 3 weeks. During this time, their body weights increased by 22%. Controls fed a nearly isocaloric oral diet were sham operated and harnessed in the same manner as their parenterally fed counterparts. Parenteral feeding resulted in a significant decrease in the weights (per 100 g body weight) of the oxyntic gland area of the stomach, small intestine, and pancreas. The weights of the spleen, testes, kidneys, and antral region of the stomach were unaltered. In the small intestine there was a significant loss of DNA and a near doubling of the RNA:DNA ratio in the parenterally fed animals. In the absence of an oral diet antral gastrin levels decreased to one-thirtieth of the control level. The following conclusions are suggested by these results. First, the oral intake and/or physical presence of food within the gastrointestinal tract are necessary for structural maintenance of some tissues of that tract. Second, the disproportionate decrease in weight that occurs in certain tissues is apparently unrelated to the absence of nutrients which might normally be utilized directly from the lumen. Third, maintenance of normal tissue stores of the hormone, gastrin, is dependent on stimuli provided by oral ingestion and the presence of food in the gastrointestinal tract.

Action of Gastrin on Gastrointestinal Structure and Function

In previous communications we have reported using the rat fed by total parenteral nutrition to examine the effects of the absence of food from the gut on functional and structural parameters of the gastrointestinal tract. In the current study three groups of animals were fed parenterally; one received a continuous infusion of pentagastrin equal to about one-half the D50 for acid secretion, another received a comparable infusion of histamine, and a third group was given only the liquid diet. These animals were compared to orally fed sham operated controls. The parenterally fed animals had significantly lower levels of antral and serum gastrin. When compared to whole body weight, the weights of the oxyntic gland area of the stomach, the pancreas, and the small intestine were significantly lower. In addition, the total and specific activities of the disaccharidase enzymes were significantly reduced. Pentagastrin prevented both the decreases in weights of the gastrointestinal tissues and the decreases in dissaccharidase activity. Histamine was without effect. We conclude that pentagastrin prevents the changes in gastrointestinal structure and function caused by the absence of food from the gut and that the trophic action of gastrin is necessary for the maintenance of the functional and structural integrity of the gastrointestinal tract.

Altered small bowel propulsion associated with parasitism.

Experiments were designed to test the hypothesis that alterations of intestinal motility accompany enteric helminth infections. Motility was measured in rats during the intestinal phase of infection with the nematode Trichinella spiralis by following the transit of radioactive chromium through the gut. Intraduodenal catheters were surgically implanted in rats. One week after the operation one group of animals was infected with 8 x 10(3) T. spiralis larvae and a second group was infected with 16 x10(3) larvae. A third group of uninfected rats served as controls. Three, four, or five days postinfection, Na2 51CrO4 was injected through the catheter into the duodenum or fasted animals and its propulsion through the small bowel was allowed to progress for 15 min. The distribution of radioactivity throughout the small intestine and cecum was then plotted as a function of gut length. Intestinal transit was increased significantly by infection. The leading edge of radioactivity transversed 100% of the gut length in infected rats and 70% in controls. The amount of injected radioactivity transversing the midpoint of the small intestine was estimated by regression equations to be 38% of the injected dose for control rats and 59 and 57% for infected groups. Increased propulsive activity in parasitized rats was associated with inflammatory changes and a significant reduction in disaccharidase levels in the gut mucosa. The latter conditions were most marked in the proximal small bowel where the majority of worms resided.

Lactoferrin Protects Gut Mucosal Integrity During Endotoxemia Induced by Lipopolysaccharide in Mice

The hypothesis that lactoferrin protects mice against lethal effects of bacterial lipopolysaccharide (LPS) is the subject of experimental investigations described in this article. Lipopolysaccharide is a powerful toxin produced by Gram negative bacteria that when injected into humans or experimental animals reproduce many of the pathophysiologic and immune responses caused by live bacteria. Lactoferrin administered intraperitoneally 1 hr prior to injection of LPS significantly enhanced the survival of mice, reducing LPS-induced mortality from 83.3% to 16.7%. Changes in locomotor and other behavioral activities resulting from LPS injection were not present in mice treated with lactoferrin. Also, histological examination of intestine revealed remarkable resistance to injury produced by LPS if mice were pretreated with lactoferrin. Severe villus atrophy, edema and epithelial vacuolation were observed in LPS-treated animals but not in lactoferrin-treated counterparts. Electrophysiological parameters were used to assess secretory and absorptive functions in the small intestine. In mice treated with LPS, transmural electrical resistance was reduced and absorption of glucose was increased. Lactoferrin treatment had no significant influence on basal electrophysiological correlates of net ion secretion or glucose absorption nor on changes induced by LPS. Collectively, these results suggest that lactoferrin attenuates the lethal effect of LPS and modulates behavioral and histopathological sequela of endotoxemia.

Gastrointestinal adaptation following small bowel bypass for obesity.

Small intestinal morphologic and biochemical changes were studied following jejuno-ileal bypass for obesity after body weight stabilization had occurred. Four patients underwent biopsy of in-continuity and bypassed jejunal and ileal segments of the small intestine 11 to 22 months after the bypass operation. Microscopically, marked mucosal villus hypertrophy of the in-continuity bowel was observed, especially in the ileum. Bypassed jejunal mucosa underwent atrophy compared with pre-bypass jejunum, whereas bypassed ileum appeared similar microscopically to pre-bypass ileum. The specific activities of mucosal disaccharidase enzymes (maltase, sucrase, lactase and trehalase) in units per mg protein remained similar to pre-bypass levels in segments of the in-continuity jejunum and the bypassed jejunum and ileum. On the other hand, elevated mucosal disaccharidase levels were measured in biopsy specimens of the in-continuity ileum. Total enzyme activity per unit length of intestine, however, was estimated to be elevated in both in-continuity jejunum and ileum secondary to mucosal villus hypertrophy. These data indicate that following small bowel bypass: (1) the in-continuity ileum undergoes greater biochemical and morphologic adaptation than the jejunum; and (2) intraluminal nutrients and chyme appear to be essential to maximal intestinal adaptation.

Tolerance to the effect of morphine on intestinal transit.

Introduction. The repeated or “chronic” injection of a narcotic analgesic, exemplified by morphine, often results in the phenomena of tolerance and physical dependence (1-3). In regard to the gastrointestinal tract, however, the responses to repeated administration of morphine are not clear. Tolerance to the effects of morphine on intestinal contractions in vitro appears to develop. The isolated ileum of the guinea pig is inhibited by morphine and tolerance develops to this inhibition (4). Also, tolerance develops to morphines stimulation of dog isolated small intestine (5). On the other hand, results on the development of tolerance to the intestinal actions of morphine in vivo are meager and conflicting. Miller and Plant monitored intraluminal pressures from the intestines of unanesthetized dogs and found that tolerance did not develop to the stimulatory effects of morphine (6). In contrast, Thor et al. monitored the myoelec-tric activity of the small bowel of the unanesthetized dog and found that tolerance did develop to the stimulant action of morphine (7). Motility functions of the small intestine can be investigated by following the transit of a nonabsorbable marker. Alterations in transit are believed to be secondary to changes in the contractile patterns of the small intestinal musculature. This study was designed to: (i) assess quantitatively whether acute injections of morphine affect intestinal transit in unanesthetized rats, and (ii) determine whether prior treatment of the rats with repeated injections of morphine produces tolerance to the observed effects. Materials and methods. Intraduodenal catheters were implanted in 32 Sprague-Dawley rats (Sprague-Dawley, Madison, Wis.) weighing 203 ± 4 g (mean ± SE). Details of implantation have been reported (8). Briefly, the animals were anesthetized with 20 mg of ketamine hydrochloride (Ke-taject, Bristol Laboratories, Syracuse, N.Y.) administered intraperitoneally.

Boosted mucosal immune responsiveness in the rat intestine by actively transported hexose

Anaphylaxis-mediated intestinal fluid secretion was measured in Trichinella spiralis- or ovalbumin-immunized rats challenged intraduodenally with T. spiralis somatic antigen (1 mg protein/0.5 mL saline) or ovalbumin (1 mg/0.5 mL saline), respectively. Intestinal fluid volume was measured 30 minutes after challenge as an index of net secretion. Challenge with the antigenic bolus containing 40 mmol/L D-glucose induced twice the fluid secretion as that induced by either antigen alone. L-Glucose was an ineffective substitute for D-glucose. The enhancement of secretion by D-glucose was dependent on prior immunologic sensitization, was diminished in the presence of phlorizin, and was mimicked by beta-methyl glucoside. Results indicate that the active transport of D-glucose augments the antigen-mediated fluid secretion, possibly by enhancing permeation of the intestinal epithelium to antigen, thereby providing greater access to the mucosal immune system.

Involvement of Type I Hypersensitivity in Rapid Rejection of Trichinella spiralis from Adult Rats

The role of type I hypersensitivity in the rapid rejection of Trichinella spiralis from actively and passively immunized rats was examined. Net intestinal fluid secretion, which occurs during the rejection of the parasites, was used to verify the expression of local anaphylaxis and was examined for its possible role in the rejection process. Worm establishment in the small intestine 30 min after intraduodenal inoculation was significantly reduced in rats that were passively immunized with immune serum containing anti-Trichinella IgE as compared with recipients of normal serum. Worm-induced fluid secretion in immune rats was completely inhibited by the combined action of indomethacin and diphenhydramine. However, worm rejection was not affected. L-651,392, a 5-lipoxygenase inhibitor, also failed to prevent rejection. Ketanserin (a serotonin S2 receptor antagonist) and MDL-72222 (a serotonin S3 receptor antagonist) together blunted the rapid rejection response and reduced fluid secretion. Furthermore, intra-arterial perfusion of serotonin into nonimmune rats caused fluid secretion and reduced worm establishment. In nonimmune rats prostaglandin E2, cholera toxin, and hypertonic Krebs-mannitol solution were used to evoke the same level of intestinal fluid secretion as that induced by reinfection in immune rats or by serotonin in nonimmune hosts. When larvae were inoculated into the secreting gut, their infectivity was unaffected. The results suggest that anaphylaxis is involved in the rapid rejection of T. spiralis in immune rats and that serotonin is a possible chemical mediator of worm rejection. Although the mode of action of serotonin in the rejection process remains unknown, its possible involvement through fluid secretion can be ruled out.

SYSTEMIC ANTI-INFLAMMATORY EFFECT ASSOCIATED WITH ENTERIC TRICHINELLOSIS IN THE RAT

The hypothesis tested was that enteric parasites that induce local inflammation in their host suppress inflammatory reactions at distant sites. A technique was developed to demonstrate, quantitatively, such an anti-inflammatory component. The systemic antiphlogistic effect produced by the intestinal stages of Trichinella spiralis was studied and compared with that caused by dexamethasone, a synthetic adrenocortical steroid. Inflammation was measured (dry weight, protein content, myeloperoxidase activity) as the amount of granulation tissue accumulated around a sterile cotton string implanted for 1 wk under the abdominal skin of rats. Based on this assay, T. spiralis infection had a systemic anti-inflammatory effect on the host which was directly dose related. Steroid treatment also had a dose-dependent suppressive effect on granuloma formation. The maximum dose (56 X 10(3) larvae/kg body weight) of T. spiralis used, had suppressive activity equivalent to 1.0 mg/kg body weight of steroid.

Mast Cell-Mediated Colonic Immune Function and Its Inhibition by Dietary Aspirin in Mice Infected with Trichinella spiralis

Because of the integrated nature of cellular elements in the gut wall, an understanding of the local mucosal immune system and its adaptive capacity should provide more insight into diseases of the colon, such as inflammatory bowel disease and colorectal cancer. To develop a method to quantify colonic mucosal immune function in situ, ion transport mediated by a type I hypersensitivity reaction was measured in the colon of mice infected with Trichinella spiralis. Segments of sensitized distal colon mounted in Ussing chambers and challenged with T. spiralis-derived antigen resulted in a rise in short-circuit current (delta Isc) that was antigen-specific and inhibited by furosemide. Colonic segments from infected, mast cell-deficient W/Wv mice were unresponsive to challenge with T. spiralis antigen. Inhibition of anaphylactic mediators with various pharmacological agents implicated prostaglandins and leukotrienes as the principal mediators of the antigen-induced delta Isc, with 5-HT also playing a role. Neural blockade with tetrodotoxin or blockade of histamine H1 receptors with diphenhydramine failed to inhibit the colonic immune response. Distal colon from immune mice fed an aspirin-containing diet (800 mg/kg powdered diet) ad libitum for 6 weeks had a decreased response to antigen. However, dietary aspirin had no effect on antigen-induced delta Isc in the jejunum or on Cl- secretagogue-stimulated delta Isc in the distal colon. These results suggest that products of arachidonic acid metabolism are important mediators of mast cell-dependent, antigen-stimulated Cl- secretion in the distal colon of mice immunized by infection with T. spiralis.(ABSTRACT TRUNCATED AT 250 WORDS)