Turnover of phosphocholine and phosphoethanolamine in ether-phospholipids of Krebs II ascite cells

Krebs II ascite cells suspended in Eagle medium were incubated at 37 C for up to 6 hr in the presence of [3H] glycerol or [32P] orthophosphate. After extraction, their lipids were treated with guinea pig phospholipase A1 under conditions where all diacyl-phospholipids (diacyl-PL) became hydrolyzed with 55% recovery of lyso-PL. Using a bidimensional thin layer chromatography (TLC) involving exposure to HCl fumes between the two runs, it then became possible to determine at once the specific radioactivity of the three subclasses (diacyl-, alkylacyl- and alkenylacyl-) present in choline glycerophospholipids (CGP) and ethanolamineglycerophospholipids (EGP). Compared to diacyl-PL, a lower de novo synthesis of ether subclasses was evidenced in both CGP and EGP by [3H] glycerol incorporation. Although the same profile was obtained for CGP with [32P] orthophosphate, the three EGP subclasses displayed in this case the same specific radioactivity. These data indicate a higher turnover rate of the polar head group of ether-EGP compared to either-CGP. The simple methodology used in the present study might thus prove helpful in developing enzymatic studies dealing with the mechanism of this accelerated renewal.

Purification and resolution of NADH diaphorase activity from NADPH diaphorase-linked: O2 oxidoreductase activity of human neutrophils

Intrinsic NADPH diaphorase activity is a component of the membrane-bound NAD(P)H:O2 oxidoreductase of human neutrophils. NADH-specific diaphorase activity is also present in membrane fractions rich in oxidoreductase activity. Studies were undertaken to determine whether the NADH diaphorase might also be intrinsic to the oxidoreductase. The latter diaphorase was freed from the membrane by detergent extraction and partially purified approximately 80-fold. Its apparent molecular weight following solubilization in deoxycholate and Tween-20 was 204 000 +/- 10 000. The specific activity of the partially purified diaphorase with ferricyanide as electron acceptor was 7.6 X 10(3) mU/mg protein, its pH optimum was 7.0, and its Km for NADH was 13 microM. It is completely devoid of NADPH diaphorase activity, lacks the capacity to reduce molecular oxygen, yet readily reduces ferricyanide, 2,6-dichlorophenolindophenol and ferricytochrome c. Whereas the NADH diaphorase was freed from the particulate fraction of cell lysates by extraction in 10 mM Tris-HCl buffer (pH 8.6) made up in 15% glycerol and 0.5% Tween-20, NADPH-dependent diaphorase and superoxide-generating activities also present in the membrane were not. These observations make it unlikely that the principal membrane-bound NADH diaphorase found in human neutrophils is a component of the NAD(P)H:O2 oxidoreductase, despite its common association in the same particulate fraction of cell lysates.

Improved method of thyroid peroxidase extraction from the human thyroid gland

This study describes a new method of solubilizing thyroid peroxidase (TPO) and partial purification of TPO from a small surgical specimen of human thyroid tissue. Graves' thyroid tissue was homogenized and centrifuged to obtain the 100 000 X g pellet. To solubilize TPO from the 100 000 X g pellet protein, the following four detergents were used: Triton X-100, digitonin, sodium deoxycholate, and 3-[(3-choramidpropyl)-dimethylammonio] 1-propanesulfate (CHAPS). For some samples, two detergents were combined and trypsin was also used. The best solubilization of TPO activity was obtained from the combination of digitonin-CHAPS-trypsin treatment or deoxycholate-CHAPS-trypsin treatment. The solubilized crude TPO was then chromatographed on a Sephacryl S 300 column. The results of chromatography indicated that detergent treatment alone did not separate TPO from other membrane proteins and the addition of trypsin was required for separation of TPO. Sephacryl chromatography of detergent-trypsin solubilized TPO was suitable as an initial step for purification of TPO from a small human thyroid tissue.

NADPH-cytochrome P-450 reductase-cytochrome b5 interactions: crosslinking of the phospholipid vesicle-associated proteins by a water-soluble carbodiimide

Detergent-solubilized and purified rabbit liver microsomal NADPH-cytochrome P-450 reductase and cytochrome b5 were coreconstituted into phospholipid vesicles. When the proteoliposomes were incubated with a water-soluble carbodiimide, 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC), a new higher-molecular-weight band was seen by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The band was purified by chromatography on DEAE-Sepharose CL-6B, 2'5'-ADP-Sepharose 4B, and Sephadex G-100. The heme absorption spectrum and fluorophotometric assay of flavin of the purified material demonstrate that this product is a 1:1 crosslinked complex containing one molecule each of the flavoprotein and cytochrome. Proteolysis of the crosslinked form indicates that the hydrophilic catalytic domains participate in the covalent attachment, and that the hydrophobic membrane-attachment peptide is necessary for the protein interaction. The purified crosslinked derivative showed no activities for reduction of either cytochrome c or ferricyanide. About half of the enzyme-associated flavin was reduced rapidly by NADPH, as was 20-30% of the crosslinked cytochrome, indicating that, in at least some of the complexes, the flavin-mediated pathway for reduction of cytochrome by pyridine nucleotide was intact. These data suggest that the output- rather than the input-electron transfer site(s) in the flavoprotein was (were) blocked by the covalently attached cytochrome.

Transmembrane orientation of the mannose 6-phosphate receptor in isolated clathrin-coated vesicles

The mannose 6-phosphate (Man-6-P) receptor is an integral membrane glycoprotein which mediates intracellular transport and receptor-mediated endocytosis of lysosomal proteins. Clathrin-coated vesicles, which have been shown to be significantly involved in these processes, have also been shown to be a major subcellular site of the receptor. In order to define the orientation of the Man-6-P receptor within the coated vesicle membrane, highly purified preparations of coated vesicles were prepared from bovine brain employing D2O/sucrose gradient centrifugation and Sephacryl S-1000 column chromatography. Using [35S]methionine-labeled lysosomal enzymes secreted by Chinese hamster ovary cells as receptor ligand, significant binding activity was detected only upon permeabilization of the coated vesicle membranes with detergent. Prior treatment of intact vesicles with proteinase K resulted in similar binding activity upon permeabilization. However, examination of the receptor by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and immunoblotting with rabbit anti-receptor serum revealed that proteinase K treatment of intact vesicles reduced the size of the receptor by 12,000 daltons. A similar decrease in size was obtained when the vesicles were treated with carboxypeptidase Y. These results suggest that the Man-6-P receptor is a transmembrane protein with its lysosomal enzyme binding site oriented toward the lumen of the coated vesicle and its C-terminal end exposed to the exterior or cytoplasmic portion of the vesicle membrane.

Effects of bile salts and prostaglandins on sodium transport in isolated rat gastric mucosa

To determine whether prostaglandins may protect against bile salt inhibition of ion transport in the stomach, gastric mucosal tissue was isolated from the rat and mounted in flux chambers. Transport of Na+ was traced with radioisotopes in the absence of bile salts and then in the presence of conjugated taurocholate or unconjugated deoxycholate at low, intermediate and high mucosal concentrations (1, 5 and 15 mmol/1). At a high (7.40) or low (3.4) mucosal pH, only the unconjugated deoxycholate inhibited active Na+ transport from mucosa to submucosa with respect to untreated controls. Inhibition of Na+ transport was apparent at a low level of deoxycholate, which also inhibited the electrical potential difference. Intermediate and high levels of deoxycholate lowered the tissue resistance. When the tissues were exposed to mucosal prostaglandin E2 or its 16,16-dimethyl analogue before and during acidified taurocholate administration, Na+ transport was not changed significantly but the electrical resistance remained high. Thus, unconjugated bile salt is more potent than conjugated bile salt in inhibiting Na+ transport and breaking the gastric mucosal barrier, and prostaglandins may afford some small protection.

Activation of nonspecific lipase (EC 3.1.1.-) by bile salts

The enzyme nonspecific lipase (EC 3.1.1.-) from rat pancreas has been isolated and its amino acid composition determined. The amino acid composition confirms more indirect evidence that nonspecific lipase is not the same enzyme as cholesteryl ester hydrolase. Activation of the enzymatic activity by bile salts has been studied by equilibrium dialysis, gel filtration, light scattering, circular dichroism and fluorescence polarization. The binding of bile salt by the enzyme is saturable and is associated with a conformational change. Upon binding cholate, the protein experiences a decrease in beta-structure with no significant change in alpha-helix content, an increase in apparent Stokes radius, a decrease in light scattering properties, and a slight decrease in polarization of the intrinsic tryptophan fluorescence. Attachment of bile salt is associated with decreased reactivity of essential sulfhydryl groups, but no detectable change in reactivity of amino groups. A change to a more nearly spherical shape upon binding bile salt would be consistent with the experimental observations, but the exact sites of binding remain uncertain.

Self-association of the seventh component of human complement (C7): dimerization and polymerization

Two association reactions of isolated C7 are described. The incubation of isolated C7 in 1% deoxycholate results in hemolytically inactive dimeric C7 that has a sedimentation coefficient of 7.3S. Dimeric C7 expressed hydrophobic domains that bound 41 +/- 4 mol deoxycholate per mol C7 and that aggregated upon removal of the detergent. The dimeric nature of the deoxycholate-treated C7 was demonstrated by analytical ultracentrifugation and by gel filtration, and yielded the following parameters: Mr = 230,000; diffusion coefficient, D = 2.9 X 10(-7) cm2/sec, and Stokes' radius, rH = 7.3 nm. Dimeric C7 exhibits an increased electrophoretic mobility and an increased beta-sheet structure, as compared with monomeric C7. Upon incubation with deoxycholate-phospholipid mixed micelles and removal of the detergent, the dimeric C7 became firmly associated with the lipid vesicles and was partially aggregated in the lipid bilayer. Trypsin treatment released approximately 50% of the protein material from the C7 vesicle complex. The other association reaction of isolated C7 occurs upon incubation with 1 M guanidine HC1; C7 forms soluble, linear protein polymers that have sedimentation coefficients ranging from 20 to 30S. The strands are 5 to 8 nm wide and vary in length between 20 to 100 nm. They tend not to aggregate, they are hemolytically inactive, and they exhibit increased beta-sheet structure, as compared with monomeric C7. They can be dissociated to hemolytically active monomers by exposure to 4 M guanidine HC1 and by subsequent 100-fold dilution with buffer. Isolated C5 or C6 did not exhibit any of these properties. The results suggest that the properties acquired by C7 in the hydrophilic-amphiphilic transition may be responsible for the expression of the membrane binding site of "metastable" C5b-7 and for the polymerization of C5b-7 within the target membrane.

Antibiotic and deoxycholate resistance in Campylobacter jejuni following freezing or heating

The surviving populations of Campylobacter jejuni serotypes following freezing or heat were found to be more sensitive to rifampicin and sodium deoxycholate on subsequent culture. Thus while control cultures had an IC50 of greater than 20 micrograms/ml rifampicin those of injured cells were less than 5 micrograms/ml. Treatment with EDTA caused almost identical changes in resistance suggesting that the altered resistance pattern of injured cells was due to loss of the barrier properties of the bacterial outer membrane.

Stimulated protein kinase activity during acute pancreatitis in rats. Possible mediation by proteolysis, lipolysis, and bile salts

The rate of protein phosphorylation, as catalyzed by the protein kinase enzymes, was measured in the pancreas of rats with acute experimental pancreatitis. Two different methods were used to induce pancreatitis in rats: retrograde injection of deoxycholate (DOC) into the pancreatic duct, or daily intravenous administration of DL-ethionine. Basal protein kinase activity was elevated in rats with acute experimental pancreatitis. This increase in activity was not dependent on free Ca2+ and did not result from elevated cAMP levels. To assess the possible role of digestive enzymes in protein kinase activation, tissue extracts from healthy controls were subjected to mild treatment with digestive enzymes and DOC. Trypsin, chymotrypsin, phospholipase A, and DOC produced protein kinase activation of a similar magnitude as found in diseased tissue. Results indicate that stimulated protein kinase activity in tissue of animals with acute pancreatitis may arise from the action of digestive enzymes.

Lipopolysaccharide-specific bacteriophage for Klebsiella pneumoniae C3

Bacteriophage FC3-1 is one of several specific bacteriophages of Klebsiella pneumoniae C3 isolated in our laboratory. Unlike receptors for other Klebsiella phages, the bacteriophage FC3-1 receptor was shown to be lipopolysaccharide, specifically the polysaccharide fraction (O-antigen and core region). We concluded that capsular polysaccharide, outer membrane proteins, and lipid A were not involved in phage binding. Mutants resistant to this phage were isolated and were found to be devoid of lipopolysaccharide O-antigen by several criteria but to contain capsular material serologically identical to that of the wild type. The polysaccharide fraction was concluded to be the primary phage receptor, indicating that it is available to the phage.

Estimation of liposome integrity by 1H-NMR spectroscopy

A fast and simple method of 1H-NMR spectroscopic control of liposome membrane integrity is suggested. The method is based on the redistribution of intensities between two singlet 1H-NMR signals--from intraliposomal marker compound (nitrilotriacetic acid sodium salt, 1H-NMR signal at 4 p.p.m.) and from its complex with Eu3+ added to the external medium (NMR signal of the complex at - 1 p.p.m.). The method permits registration of the kinetics of liposome destruction under the action of detergent or serum. It is shown that the presence of cholesterol in the membrane makes it more stable.

Prostaglandin E2 counteracts the inhibition by indomethacin of rat colon ornithine decarboxylase induction by deoxycholic acid

The mechanism whereby bile acids promote colon tumor development was studied. Bile acids increase intestinal ornithine decarboxylase (ODC), an effect that is suppressed by indomethacin, an inhibitor of prostaglandin (PG) synthesis. Male Sprague-Dawley rats were pretreated with 0.002% indomethacin solution in drinking water for 3 days, then given a single intrarectal instillation of 20 mg of deoxycholate and/or 1 mg of PGE2. Four hours later, the rats were killed, and the ODC activity was measured in the mucosa of the distal large bowel. ODC was significantly lower in rats given indomethacin plus deoxycholate than in those given deoxycholate alone, but it was significantly higher in rats treated with indomethacin and PGE2 plus deoxycholate. Without deoxycholate, indomethacin plus PGE2 did not elevate ODC compared with indomethacin alone or no treatment. Indomethacin reduced the colonic mucosal PG level. Thus, PGE2 mediates the deoxycholate-induced colonic mucosal ODC activity, and overcomes the inhibition of this enzyme activity by indomethacin. It is concluded that the anti-promoting effect of indomethacin in colon carcinogenesis, previously demonstrated, may result from the indomethacin inhibition of PG synthesis.

Protection by dietary proteins against the effects of bile acids on rat jejunum and stomach

Because bile acids bind to certain proteins we examined whether the effect of dihydroxy bile acids on jejunal water transport and gastric mucosal function could be blocked by the presence of protein. In the rat jejunum 2.5% bovine serum albumin blocked the secretion of water and electrolytes induced by 2 mM deoxycholate, whereas 5% ovalbumin, which does not bind bile acids, had no effect. Bovine serum albumin protected large unilamellar liposomes from damage by taurodeoxycholate and reduced the monomer concentration of taurodeoxycholate, whereas ovalbumin afforded no protection. In equilibrium dialysis studies whey protein and bovine serum albumin reduced the free taurodeoxycholate concentration (150 mM HCl enhanced this effect). In the rat stomach taurodeoxycholate (2.5 or 10 mM) in the presence of 150 mM HCl reduced potential difference and enhanced sodium secretion and hydrogen ion loss. These effects were reduced in the presence of whey protein. We conclude that proteins that bind bile acids have the potential to protect mucosal membranes from the adverse effects of bile acids.

Acyl chain specificity and kinetic properties of phospholipase A1 and A2 of bone marrow-derived macrophages

The fatty acyl specificity of phospholipase A1 and A2 in homogenates of mouse bone marrow-derived macrophages was determined using phosphatidylcholine and phosphatidylethanolamine of different acyl chain composition. Phosphatidylcholine with arachidonoyl at position 2 was cleaved preferentially by an alkaline phospholipase A2 (pH-optimum 9.0) leading to selective liberation of arachidonic acid. In contrast, phosphatidylcholines with oleoyl or linoleoyl at position 2 were degraded mainly by an acid phospholipase A1 (pH-optimum 4-5) resulting in a conservation of these fatty acids esterified in lysophosphatides. Substrate kinetics of the alkaline phospholipase A2 revealed a 30 fold higher affinity (Km = 3.8 X 10(-7) M) for 1-acyl-2-arachidonoyl-glycerophosphocholine compared to 1-acyl-2-oleoyl-glycerophosphocholine. The kinetic data were not influenced by endogenous lipids indicating that exogenous substrates do not equilibrate with cellular lipids. These results are suitable to explain a selective liberation of arachidonic acid from a mixture of phospholipids.

Reversible inactivation and reactivation of vaccinia virus by manipulation of viral lipid composition

The role of phospholipids in vaccinia virus was investigated by substituting viral lipids with specific phospholipids. Treatment of virus with sodium dodecyl sulfate, sodium deoxycholate, or Nonidet-P40 (NP-40) resulted in almost complete removal of viral lipid and led to inactivation of the virus. The inactivation induced by the former two was irreversible, but NP-40-treated virus was reactivated upon reassociation with phospholipids. Individual phospholipids, including phosphatidylserine (PS), phosphatidylcholine, phosphatidylethanolamine, phosphatidylinositol, lysolecithin, sphingomyelin, and acyl bis(monoacylglycero)phosphate (ABMP), were tested for ability to reactivate NP-40-treated virus. Reactivation was induced only by PS. The infectivity of virus that had been treated with NP-40 and then with PS was unstable; the reactivated virus was inactivated within a short period. It was also very sensitive to trypsin. Treatment of NP-40-treated virus with mixtures of PS and ABMP yielded virus that was more resistant to spontaneous and trypsin-induced inactivation. Thus, PS appears to be an essential for infectivity and ABMP appears to play a supplementary role for maintenance of infectivity, perhaps by protecting against inactivating factors.

Effects of sulfodeoxycholate on rat and rabbit small intestine

To determine how sulfation alters the biological properties of dihydroxy bile acids, we compared the effects of 3-sulfodeoxycholate (SDC) and deoxycholate (DC) in the rat and rabbit intestine. While 5 mM DC induced water and electrolyte secretion and inhibited glucose absorption in the rat, SDC enhanced jejunal and ileal water and solute absorption. SDC had no effect in the rabbit ileum. In the rat jejunum DC caused mucosal injury and enhanced mucosal permeability while SDC had no effect. In vitro in the rabbit ileum, 10 mM SDC enhanced net sodium flux and decreased net residual flux, while 0.5 mM DC reduced net sodium flux and induced Cl- secretion. Both bile acids increased short-circuit current and potential difference and decreased tissue conductance. During reversed-phase, high-performance liquid chromatography SDC was more polar than DC. Sulfation reduced the ability of DC to destroy large unilamellar liposomes by a factor of 10. Thus, sulfation abolishes the effects of DC on the intestine by enhancing the polarity of this molecule. The enhancement of intestinal solute and water absorption by SDC requires further study.

Sodium deoxycholate promotes the absorption of heparin administered orally, probably by acting on gastrointestinal mucosa, in rats

Sodium deoxycholate (DOC), selected as a promoter of gastrointestinal absorption of heparin, was administered orally to rats, followed, at increasing intervals, by heparin. Maximal plasma clearing activity (PC) was obtained with a 60-min interval, though PC was still elicited after 24 h, suggesting that DOC acts on the gastrointestinal mucosa. Inhibition of blood coagulation was also observed after oral heparin. The suggestion that DOC increases heparin absorption is supported by increased plasma levels of heparin. No signs of several gastrointestinal damage were seen.

Measurement of active constitutive beta-D-glucosidase (esculinase) in the presence of sodium desoxycholate

The hydrolysis of esculin in the presence of bile has been utilized for many years for the identification of bacteria. It is especially useful in differentiating species of the genus Streptococcus. The procedure is a two-step one. First, the bacterium must grow in a particular concentration of bile, and second, it must hydrolyze esculin. The hydrolysis of esculin has traditionally been determined by the brown-black color that results when one of the hydrolysate products, esculetin, reacts with iron in the medium. The procedure requires incubation for 24 h or more. A method was developed based on the measurement of constitutive beta-glucosidase (esculinase) with the repression of this enzyme by bile equivalent (sodium desoxycholate) that required only 30 min. p-Nitrophenyl-beta-D-glucopyranoside was the esculinase substrate, and sodium desoxycholate was substituted for bile salts. After inoculation, a yellow color was equivalent to the brown-black seen in the 40% bile-esculin reaction. The reagent was dispensed in test tubes and was stable for 6 months. The 30-min procedure correlated well with the conventional 24-h bile-esculin agar tube. Streptococcus pneumoniae could also be identified because of the rapid lysis it exhibited in the substrate solution.

Changed sensitivity to antigen in a gut epithelium treated with bile salts

Colonic epithelia from guinea-pigs, sensitized by feeding with cow milk, responded to antigen (beta-lactoglobulin) challenge when applied to the serosal, but not the mucosal, side of the tissue. The response, under short circuit conditions, was an inwardly directed current due to chloride secretion. Two detergents, deoxycholate and Triton X-100, caused the basal short circuit current to decrease and transepithelial conductance to increase when applied to the mucosal surface. After removing detergents from the bathing solution tissues now responded to antigen challenge from the mucosal side, without impairment of the overall response. There was a correlation between the conductance change induced by detergents and the fraction of the total response which could be elicited form the mucosal side of the tissue. It was concluded that models of local hypersensitivity reactions to ingested foodstuffs require both development of immunological sensitivity plus increased permeability to antigen. The role of bile salts in inducing the latter is discussed.

Characterization of extracellular phospholipase A2 in rheumatoid synovial fluid

Phospholipase A2 (PLA2) activity has now been identified in rheumatoid synovial fluids. This PLA2 is a calcium-requiring protein of MW 11,000 with a neutral pH optimum. Its activity was inhibited by high concentrations of Mg2+, and by the active site-directed histidine reagent p-bromophenacyl bromide. Ionic and nonionic detergents, or the sulfhydryl reagent dithiothreitol caused loss of enzyme activity. Synovial fluid PLA2 did not interact with sulphated mucopolysaccharides such as heparin or chondroitin sulphate. Release and sequestration of PLA2 in the joint space may contribute to the characteristic rheumatoid inflammatory changes.

Behaviour of cardiac microsomal Ca2+ pump under conditions that may simulate pathological situations

The behaviour of Ca2+ ATPase activity in relation to Ca2+ transport process was studied under different experimental conditions in canine cardiac microsomal fraction predominantly containing sarcoplasmic reticulum. The total Ca2+ concentration required for half maximal activation (Ka) of microsomal Ca2+ ATPase and Ca2+ uptake did not differ significantly, unless 0.1 mmol/l EGTA was present in the incubation media. Pretreatment of cardiac microsomes with membrane disruptive agents like phospholipase A, trypsin as well as deoxycholate strongly increased (2-3 fold) Ca2+ ATPase activity but uptake rate of Ca2+ declined. Only in phospholipase C and beta-glucuronidase pretreatment, a parallel decrease of Ca2+ ATPase and uptake was observed. In presence of excess (free)Ca2+ (greater than 10 mumol/l) both Ca2+ ATPase as well as Ca2+ uptake were inhibited, however, Ca2+ binding process remained unaltered. Likewise, low pH completely altered the relation between Ca2+ binding and ATPase activity; whereas Ca2+ ATPase was inhibited, Ca2+ binding did not change. Our present data provide evidence for some cellular factors that may be involved in producing uncoupling of microsomal Ca2+ ATPase from Ca2+ accumulation process that was previously observed in various pathological situations.

Mechanisms underlying the intestinal fluid secretion evoked by nociceptive serosal stimulation of the rat

Intestinal net fluid transport was measured in vivo continuously with a gravimetric method. Chemical stimulation of the jejunal serosa with hydrochloric acid (0.1 M), ethanol (20%), cat bile or 7-deoxycholic acid (10 mM) evoked an intestinal fluid secretion. Hexamethonium (10 mg/kg b.wt.i.v.) or serosal application of lidocaine (1% solution) partially blocked this secretory response. Bradykinin and prostaglandin E1, two important inflammatory mediators, elicited fluid secretion when applied to the serosal surface at a concentration of 10(-4) M. This secretion was also partly inhibited by hexamethonium. Furthermore indomethacin (10 mg/kg b.wt. i.v.) or pyrilamine (10 mg/kg b.wt. i.v.), a H1-receptor blocker, partly inhibited the secretory response caused by chemical stimulation of the serosa while cimetidine (1 mg/kg b.wt. i.v.), a H2-receptor blocker, had no effect. Freeze sectioned samples from chemically stimulated intestines were examined by fluorescence microscopy. A leakage of i.v. administrated Evans blue labelled albumin into the interstitial space of the serosa and the outer layer of the muscularis was found. It is concluded: The intestinal fluid secretion studied is mainly elicited by nociceptive stimulation of nerves in the serosa or the outer muscularis. The reflex may be activated by the local release of histamine, kinins and prostaglandins. The reflex studied is part of an inflammatory response.