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1.
The effect of cholera toxin, heat labile and heat stable Escherichia coli enterotoxin on mucosal cyclic AMP concentrations was determined on the proximal jejunum of weanling pigs and young rabbits. Ligated loops were injected with solutions containing no enterotoxin for control and either cholera toxin, heat labile or heat stable E. coli enterotoxin. The loops were drained after either two, four or six hours incubation at which time accumulated fluid was recorded and mucosal samples removed for determination of cyclic AMP concentration. In the rabbit, cholera toxin and heat labile, but not heat stable E. coli enterotoxin stimulated intestinal secretion while in the pig all three enterotoxins induced net fluid accumulation. Cholera toxin and heat labile, but not heat stable E. coli enterotoxin elevated rabbit mucosal cyclic AMP concentrations. In the pig these enterotoxins had no significant effect on mucosal cyclic AMP concentrations. The results are inconsistent with the hypothesis that the adenyl cyclase system is an essential step for enterotoxin induced intestinal secretion. The activation of intestinal adenyl cyclase by bacterial enterotoxins may only be an associated and not a necessary event for the stimulation of intestinal secretion.  相似文献   

2.
The effect of heat stable and heat labile Escherichia coli enterotoxins or cholera toxin in combination with theophylline on net water, sodium and chloride and unidirectional sodium and chloride fluxes was examined in acute isolated loops of jejunum of weanling swine. The effect of heat stable enterotoxin in combination with theophylline was determined in loops located in the proximal jejunum, while combinations of theophylline and either heat labile enterotoxin or cholera toxin were studied in the distal jejunum. In each situation the addition of theophylline resulted in an additive rather than a synergistic increment of intestinal secretory activity. This study implies that the intestinal adenyl cyclase system and enterotoxin induced intestinal secretion may not be directly related in the swine small intestine.  相似文献   

3.
The B subunit of cholera toxin has been covalently attached to the surface of liposomes made from a mixture of phosphatidylethanolamine, phosphatidylcholine and cholesterol. Adenylate cyclase inhibitors and chloride conductance inhibitors were encapsulated within the liposomes. These "targeted" liposomes were used to study the combined effects of this novel delivery system, and a limited number of possible antisecretory agents, on net fluid flux into the pig jejunum. A state of net secretory fluid flux was induced in isolated jejunal loops in weanling pigs by adding theophylline or cholera toxin to the lumen of the isolated loops. There was no reduction in net fluid secretion when liposome suspensions without encapsulated secretory inhibitors were added to fluid in the lumen of loops treated with theophylline. There was also no reduction in net fluid secretion when miconazole, alpha-phenylcinnamate or 5 nitro-2-(3-phenethylamino)benzoate were encapsulated within targeted liposomes added to isolated jejunal loops. The net fluid flux induced by exposure of jejunal loops to theophylline was significantly reduced by adding targeted liposomes containing 2'-deoxy-3'-AMP. The reduction involved a reversal of net secretory fluid flux to an absorptive value. The net fluid secretory response to treatment of loops with cholera toxin was also inhibited by treating loops with targeted liposomes containing 2'-deoxy-3'-AMP. However, the reversal of secretion was less complete for secretion induced by cholera toxin than for secretion induced by theophylline. The reduced antisecretory efficacy versus cholera toxin was not improved by encapsulating higher concentrations of 2'-deoxy-3'-AMP.(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   

4.
The effect of a heat-stable enterotoxin of Escherichia coli was compared with that of theophylline on ion transport in the pig jejunum, using both in vivo and in vitro techniques. The maximal electrical response to heat-stable enterotoxin was only one-half that of theophylline even though the magnitude of the net secretory response was similar. A net, active secretion of HCO3 was partially responsible for the secretory response induced by heat-stable enterotoxin, whereas theophylline induced an active secretion of chlorine which could account for the entire secretory response. Heat-stable enterotoxin elevated tissue cyclic guanosine monophosphate levels, whereas theophylline elevated both cyclic adenosine monophosphate and cyclic guanosine monophosphate. Cyclic guanosine monophosphate levels induced by heat-stable enterotoxin were markedly potentiated by theophylline. Results suggest that HCO3 secretion in the pig jejunum may be controlled by the cyclic guanosine monophosphate system and this system also activates a neutral secretory process which at high heat-stable enterotoxin doses accounts for the bulk of the net secretion observed. Conversely, the chlorine secretion elicited by theophylline is entirely electrogenic and is consistent with results obtained in other species.  相似文献   

5.
Acute, isolated loops of proximal and distal jejunum of weanling swine were exposed to either heat stable porcine Escherichia coli enterotoxin, heat labile porcine Escherichia coli enterotoxin, cholera toxin or theophylline. Unidirectional sodium fluxes in response to heat stable in the proximal jejunum were dependent on the length of time that the intestinal mucosae was exposed to the enterotoxin. Net water, sodium and chloride and unidirectional sodium and chloride flux measurements in the proximal jejunum in response to each agent uniformly indicated that net secretion of fluid and electrolytes was the result of increased unidirectional sodium secretion or blood-to-lumen flux and decreased unidirectional chloride absorption or lumen-to-blood flux. In addition heat stable cholera toxin and theophylline but not heat labile decreased unidirectional chloride secretion a small but significant amount in the proximal jejunum.

Sodium and chloride flux measurements in the distal jejunum demonstrated that all four secretory agents could stimulate net secretion of water, sodium and chloride in that region. The response to these secretory agents as measured by sodium and chloride unidirectional flux rates was not similar to changes observed in the proximal jejunum. In the distal small intestine, whereas heat labile cholera toxin and theophylline induced similar qualitative changes in unidirectional sodium and chloride fluxes, that induced by heat stable differed.

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6.
The Escherichia coli heat-stable enterotoxin (STb) is the most prevalent toxin associated with diarrheagenic E coli isolates of porcine origin. Unequivocal biological activity of this toxin has been observed only in swine intestine. In this study, when endogenous protease activity was blocked with soybean trypsin inhibitor, intestinal secretion was stimulated by STb in jejunal loops of rats, mice, calves, and rabbits. Compared with pigs, rats, mice, and calves, rabbits were relatively insensitive to STb. These data demonstrate that the activity of STb is not a species-specific toxic activity; there is species variation in sensitivity to STb, and some common laboratory animals may have potential to be used to measure biological activity of STb.  相似文献   

7.
Compounds that prevent chloride transport in membrane vesicles have been tested for in vivo activity against the effects of intestinal secretory agents. Chloride channel blockers including diphenylamine-2-carboxylate, 4-acetamido-4'-isothiocyanostilbene-2,2'-disulfonate, 5-nitro-2-(2-phenylethylamino)benzoic acid, and alpha-phenylcinnamic acid were tested for effects on jejunal or ileal secretion in weanling pigs. Secretion was studied in ligated intestinal loops in a control state, during exposure to secretory concentrations of theophylline, and after prior treatment with cholera toxin. Increases in net fluid flux induced by either theophylline or cholera toxin were not prevented by adding chloride channel blockers into the intestinal lumen. Channel blocker concentrations that reduced chloride transport by greater than 50% in pig jejunal brush border vesicles did not cause significant changes in unidirectional blood to lumen chloride flux measured in situ. Several routes of administration of the specific chloride channel blocker alpha-phenylcinnamate failed to reduce fluid secretion induced by theophylline. Chloride channel blocker effectiveness appears to be significantly different between in vitro and in vivo experimental models. In contrast to the chloride channel blockers, loperamide significantly reduced net fluid and chloride flux in ileal loops secreting fluid in response to theophylline. Antagonism of the production or actions of second messenger by loperamide was more effective than the chloride channel blockers in reducing conductive chloride transport associated with intestinal secretion.  相似文献   

8.
Glucose, l-alanine, l-aspartate, l-methionine and glycine enhanced net fluid and electrolyte absorption in acute isolated loops of the proximal jejunum of weanling swine. The effect of glucose on intestinal secretion induced by heat stable and heat labile Escherichia coli entero-toxin, cholera toxin and theophylline was examined in both the proximal and distal jejunum of weanling swine. In the proximal jejunum glucose enhanced the rate of net fluid and electrolyte absorption. This increase was accompanied by an increase in unidirectional dosium absorption. In loops exposed to either heat stable or heat labile enterotoxins, glucose significantly decreased the rate of net fluid and electrolyte secretion. The magnitude of glucose enhancement in loops exposed to heat stable and heat labile enterotoxins was similar to adjacent control loops. However, glucose enhancement did not occur in loops exposed previously to cholera toxin or concurrently to theophylline. Therefore, cholera toxin and theophylline may inhibit substrate dependent sodium absorption in the proximal jejunum. In the distal jejunum glucose enhancement did occur but the rate of enhancement was less than in the proximal jejunum. In this region glucose enhancement was not evident in loops exposed to either theophylline, heat stable, heat labile or cholera toxin.  相似文献   

9.
The inhibitory effect of salicylates on intestinal secretion in 1- to 5-day-old calves given Escherichia coli heat-stable enterotoxin (ST)-induced intestinal fluid response was investigated. Purified ST was diluted in isotonic saline solution to obtain 1:10, 1:25, 1:50, 1:75, and 1:100 dilutions. Each dilution (1 ml) was inoculated into ligated loops in the distal part of the jejunum of each calf. Acetylsalicylic acid (aspirin) given orally (100 mg/kg) at 4 hours before ST was inoculated did not substantially alter the intestinal fluid response to ST. Sodium salicylate (IV) infusion, begun simultaneously when, or at 1 hour after, ST was inoculated, significantly (P less than 0.05) decreased fluid accumulation in those loops inoculated with ST dilutions of 1:25 or greater. The sodium and potassium concentrations of the accumulated fluid did not differ significantly between or within treatment groups. These results indicate that sodium salicylate infusion may be beneficial in treating enterotoxic colibacillosis in calves. Aspirin given orally at the dose used in the present study, would not have any beneficial effect.  相似文献   

10.
The involvement of Ca++ ions as secretory mediators in pig jejunal epithelia has been investigated with an in vitro system. Omission of Ca++ from the Ringer-HCO3 bathing media on both sides of the tissue had minor effects on the basal electrical activity of pig jejunal mucosa. There were only slight decreases in transepithelial potential difference and increases in conductance with Ca++ free media. Low EGTA concentrations which reversibly blocked potential difference responses to secretory agents also had minimal effects on basal electrical activity. The in vitro secretory responses to A23187, to theophylline, and to Escherichia coli heat-stable enterotoxin were all eliminated by Ca++ depletion and restored by replacing normal Ca++ concentrations in the bathing media. Dantrolene prevented the secretory response but not the potential difference increases caused by heat-stable enterotoxin and A23187, suggesting that intracellular Ca++ stores may be reservoirs of secretory signal agent. Verapamil only blocked the secretory response to heat-stable enterotoxin. Chlorpromazine had negligible effects on basal conditions, but totally blocked both the secretory response and the Ca++-dependent effects of A23187 and heat-stable enterotoxin on potential difference. The response to theophylline was only partially inhibited by chlorpromazine, implying some involvement of both cAMP and Ca++ as secretory signals for theophylline. Cytoplasmic Ca++ concentrations appear to be at least as important as cyclic nucleotides in regulating the secretory effects of pig jejunum.  相似文献   

11.
The role of Escherichia coli as a causative agent of diarrhea in cats was investigated. Isolates of E coli from healthy and diarrheic cats were serotyped and investigated for their biochemical characters, production of cytotoxin activity on Vero cells, heat-labile enterotoxin, heat-stable enterotoxin, and hemagglutination of erythrocytes from other animal species. None of 48 investigated strains produced heat-labile enterotoxin or heat-stable enterotoxin, nor did they agglutinate erythrocytes. Most strains were hemolytic and belonged to O-serotypes 2 and 6. Cytotoxin activity on Vero cells was significantly more common and produced in greater amounts among E coli strains isolated from diarrheic cats, and was neutralized by anti-Shiga-like toxin I serum.  相似文献   

12.
Villous atrophy and crypt hyperplasia were induced in the jejunal epithelium of thirteen 3-week-old pigs by inoculation with transmissible gastroenteritis virus. The responses (changes in net fluid movement) induced in ligated intestinal loops of these pigs by intraloop injections of prostaglandin E1 (PGE1) or Escherichia coli broth culture filtrates containing either or both E coli heat-stable enterotoxins (STa and STb) were compared with the responses induced by these preparations in littermates not inoculated with virus. Villous atrophy was associated with a marked decrease in response to preparations containing STa, STb, or STa + STb, but the response to PGE1 was undiminished. These results were consistent with the reports of others that the response to cyclic adenosine monophosphate-mediated secretogogues (PGE1) is a function of crypt epithelium; however, the present results also suggest that the secretory response to STa and to STb is dependent on the integrity of the villous epithelium. In the present study, loss of villous epithelium was associated with loss of response to STa and STb, but not to PGE1.  相似文献   

13.
The objective of this study was to determine whether exposure of swine jejunum to crude culture filtrates containing Escherichia coli pig-specific, mouse-negative, heat-stable enterotoxin (STb) induces structural alterations in the jejunal mucosa of pigs. Two ligated intestinal loops in each of twelve 3-week-old pigs were exposed for 2 hours to sterile E coli culture filtrates from each of the following strains: 431 (STa-producing), 1261 (STa and STb-producing), and 1790 (STb-producing); recombinant strain HB101-pRAS-1 (STb-producing); the nontoxigenic K-12 variant HB101; or trypticase soy broth. Formalin-fixed sections from these loops were examined for sloughed cells around villi, and a lesion score was determined, indicating a change in villous epithelium from columnar to cuboidal or squamous cell types or to discontinuous epithelium. Villous lengths and crypt depths also were determined. For loops exposed to culture filtrates containing STa and STb or containing only STb, lesion scores and numbers of sloughed cells were greater (P less than 0.05) and villous length was shorter (P less than 0.01) than in loops not exposed to toxin. For loops exposed to culture filtrates containing STa, lesion scores, villus lengths, and numbers of sloughed cells were not different from those of loops not exposed to toxin. Therefore, exposure of swine jejunum to STb induced structural alterations in intestinal mucosa (ie, loss of villous absorptive cells and partial atrophy of villi) that were consistent with those causing compromised absorptive capacity.  相似文献   

14.
The effect of the cyclooxygenase and prostaglandin E2 (PGE2) synthesis inhibitor, indomethacin, on the secretory responses induced by Salmonella serotype Typhimurium (ST) and cholera toxin (CT), in the porcine small intestine was investigated. ST (10(10) colony-forming units) and CT (56 micrograms) were instilled in tied-off intestinal loops in young anaesthetized pigs receiving intravenous indomethacin in a total dose of 7.5 mg/kg, or saline. The accumulated fluid in the loops and the luminal content of endogenous secretagogues PGE2 and 5-hydroxytryptamine (5-HT) were measured. ST induced fluid accumulation in the jejunum, whereas CT induced fluid accumulation in the jejunum and ileum. Indomethacin had no effect on the secretory responses. Indomethacin had a significant effect on the luminal content of PGE2 in jejunal ST and CT loops, whereas no effect of indomethacin was observed on the luminal content of 5-HT in ST and CT loops. In ST and CT loops, an increased content of PGE2 and 5-HT compared with test loops infused with Ringer's solution was observed. These results indicate that the porcine jejunal secretory response to ST and CT does not involve prostaglandins although indomethacin has an influence on the luminal release of PGE2 but not of 5-HT.  相似文献   

15.
The effects of Escherichia coli heat-stable enterotoxin (ST) on chloride efflux rate were investigated in 3 fractions of enterocytes isolated in a villus-to-crypt gradient from porcine jejunum. There was no difference in chloride efflux rates between mature and immature cells from controls. Heat-stable enterotoxin significantly increased chloride efflux in all fractions. Morphine inhibited ST-augmented secretion in mature enterocytes. Atropine or clonidine had no effect. Calcium efflux rates and glucose or glutamic acid metabolism were not altered by ST. The results indicate that ST may stimulate chloride secretion in both villus and crypt cells and that opiates inhibit intestinal secretion by a direct action on villus epithelial cells.  相似文献   

16.
In contrast to cholera enterotoxin and other Escherichia coli enterotoxins, a pig-specific, heat-stable E. coli enterotoxin (STb) causes morphologic lesions (loss of villous epithelial cells and partial villous atrophy). These lesions reflect a loss of absorptive cells and thus suggest that STb causes impaired absorption as well as inducing net secretion. The present studies assess functional significance of morphologic changes induced by STb. Net fluid movement, mucosal surface area, sucrase activity and the electrical response induced by alanine were measured in swine jejunal loops exposed to E. coli culture filtrates with and without STb. Net fluid secretion (-11.1±1.1 ml) occurred in some STb loops (secretors) and net absorption (2.7±0.3 ml) in others (nonsecretors), but net absorption occurred in all control loops (4.9±0.2 ml). The mucosal surface area of Stb loops was about 20% less than that of controls (P<0.01). Sucrase activity was also lower (about 15%) in STb loops than in control loops (P<0.01). The electrical response induced by alanine in mucosa from nonsecreting STb loops did not differ from that induced in mucosa from control loops. However, the response to alanine in mucosa from secreting STb loops was reduced about 70% from that in mucosa from nonsecreting STb loops or from control loops (P<0.05). It is concluded that reduced sucrase activity is a functional correlate to villous atrophy induced by STb, that STb impairs alanine absorption in some loops (secretors), and that the impaired alanine absorption is independent of the decreased surface area caused by Stb. Because the impaired alanine absorption occurred independent of the decreases in surface area, it is suggested that the secretory response to STb is associated with an impairment of active absorption of alanine.  相似文献   

17.
Thirty-two Escherichia coli colonies were taken from the primary step of cultivation of the jejunal contents of each of 10 dead piglets which had suffered from diarrhea. The organisms of each colony were examined for the presence of adhesion fimbria (F4 (K88) and F5 (K99)), production of heat-stable and heat-labile enterotoxin and of colicins.The presence of heat-labile enterotoxin in the intestinal content of the necropsied pigs was also tested, and results correlated with enterotoxin production of the isolated E. coli strains. In all but 3 pigs, 50–80 % of the E. coli strains were found to produce one or both of the enterotoxins and to possess the F4 of the F5 antigen. All bacteria producing both heat-labile and heat-stable enterotoxin proved to belong toi O group 149 and to possess the F4 antigen. Strains from 1 pig belonged to O group 64 and possessed the F5 antigen; these bacteria produced heat-stable enterotoxin only. Most of the enterotoxin-producing E. coli also produced colicins.After each subcultivation, the strains produced less heat-labile enterotoxin, some becoming negative when assayed.  相似文献   

18.
Fourteen strains of Escherichia coli of serogroups characteristic of porcine class 2 enterotoxigenic E. coli isolated from pigs or calves were selected for genetic studies. The strains were examined for their ability to cotransfer a number of plasmid-mediated properties during conjugation with E. coli K-12. These properties were antibiotic resistance, and the production of heat-stable enterotoxin, the K99 antigen and colicin and the ability to ferment raffinose. Distinction was made between the two types of heat-stable enterotoxin, STa and STb. All 14 strains were antibiotic resistant and 11 of them cotransferred antibiotic resistance and heat-stable enterotoxin. One strain which transferred heat-stable enterotoxin also transferred the raffinose gene. Among six K99-positive strains which transferred heat-stable enterotoxin, five always cotransferred K99. Three strains had 100% cotransfer of colicin as well as heat-stable enterotoxin and K99. Drug resistance determinants were cotransferred at high frequency with heat-stable enterotoxin for six of eight multiple drug resistant enterotoxigenic E. coli. A 100% cotransfer of combinations of heat-stable enterotoxin, K99, colicin and antibiotic resistance was often associated with a single plasmid band on agarose gel electrophoresis. For some strains, the genes for STa and STb were on the same plasmid and for others they were on separate plasmids. The enterotoxin plasmids ranged in size from 5.2 to 85 Mdal. Heterogeneity in molecular size occurred among enterotoxin plasmids in E. coli of the same serogroup and recovered from the same animal host species.  相似文献   

19.
A toxoid prepared from the toxin of Vibrio cholera was adjuvanted with aluminium hydroxide and used for immunisation of pregnant gilts. Litters of these and of non-vaccinates were experimentally challenged with Escherichia coli producing either heat labile and heat stable (LT and ST) enterotoxins or ST enterotoxin only. Both the challenge strains of E coli produced high rates of mortality (64 and 68 per cent) and morbidity (80 and 100 per cent) in litters of non-vaccinated dams. Statistically highly significant protection against the LT/ST enterotoxin producing strain of E coli was obtained accompanied by the absence of colonisation of the small intestine by the pathogen. No protection against the ST enterotoxin producing strain was found. It is suggested that this vaccine would not confer passive protection to piglets against K99 and 987-positive E coli which usually produce ST enterotoxin only.  相似文献   

20.
A total of 476 Escherichia coli isolated from weaned pigs with diarrhea and/or edema disease were screened for the presence of the enteroaggregative E. coli heat-stable enterotoxin 1 (EAST1) gene by polymerase chain reaction (PCR). E. coli strains that carried EAST1 genes were also tested by PCR for the presence of genes for five fimbriae (F4, F5, F6, F18 and F41), two heat-stable (STa and STb) and one heat-labile (LT) enterotoxin, and Shiga toxin 2e (Stx2e). One hundred and forty nine (31.3%) of the 476 E. coli isolates carried the gene for EAST1. Of these 149 isolates, 66 (44.3%) carried the east1 gene only and 83 (55.7%) carried genes for the fimbrial adhesins or enterotoxins. E. coli which carried east1 gene also possessed genes for STa or F4 frequently. EAST1 may represent an additional determinant in the pathogenesis of E. coli diarrhea in weaned pigs.  相似文献   

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