Inhibition of intestinal sugar transport by phenformin.

The effect of phenformin on the absorption of D-glucose and D-galactose by hamster and rat intestine, was studied. Phenformin did not affect D-glucose absorption by rat intestine, but it inhibited at 10(-3) to 10(-2) M the absorption of D-glucose and D-galactose by hamster intestine. The inhibition was higher when D-glucose was tested. Phenformin also inhibited active accumulation of these sugars by rings of hamster small intestine, in vitro; this effect was greater when D-glucose was utilized. The drug inhibits the oxygen uptake in the tissue in the absence or in the presence of added substrate. Phenformin, as previously suggested, does not seem to act as a specific inhibitor on D-glucose transport, but most likely by its inhibitory effect on mitochondrial respiration.     

Inhibition by cadmium of D-galactose and L-phenylalanine transport by rat intestine in vitro

The effect of cadmium (CdCl2) on galactose and phenylalanine uptake by rat everted intestinal rings has been studied. The rings were preincubated (15 min) and incubated (5 min) in the presence of Cd. Galactose uptake (from 0.5 mM to 10 mM) was inhibited by 0.5 mM Cd about 25%. Only the phlorizin-dependent galactose transport was affected by cadmium, being a non-competitive type inhibition. A 15 min washing with saline solution significantly reduced the cadmium induced inhibition, which was practically reversed by washing with 5 mM EDTA. The uptake of 0.5 mM phenylalanine was not affected by 0.5 mM Cd but it was depressed by 1 mM Cd. Such inhibition was exerted on the sodium-dependent phenylaline transport. Washing with 5 mM EDTA diminished only slightly the inhibition of the transport by cadmium. It is suggested that the inhibition of intestinal transport of galactose and phenylalanine by cadmium may be due to its reversible interaction with metal-binding ligands, possibly sulfhydryl groups, related to the luminal transport systems.     

Paraquat effect on the bioelectric parameters of the rabbit small intestine and its in vitro penetration

The effect of paraquat (in concentrations of 10(-4) and 10(-3) mol/l) was studied on the bioelectric parameters of rabbit small intestine. A short-lasting rise in the potential difference (PD) and some decrease of tissue resistance (R) were observed, particularly after the higher concentration. These changes indicate stimulation of the transport function of the rabbit small intestine as a result of administration of this herbicide. Other tested parameters included determination of the rate of paraquat penetration (at concentration gradient 10(-3) mol/l) across the intestinal wall from the serosal side to the mucosal side and conversely. In the latter case three experimental models were used: first--complete intestinal wall, second--intestinal wall with the serosa stripped off, and third--intestinal wall with the mucosa and serosa removed. Differences were found in these rates depending on the model used. The importance of epithelial cells of the mucosa and subepithelial layers, and mesothelium of the serosa in limiting the penetration of bipirydylium herbicides is stressed.     

Receptor binding of pancreatic spasmolytic polypeptide (PSP) in rat intestinal mucosal cell membranes inhibits the adenylate cyclase activity

The recently isolated pancreatic spasmolytic polypeptide, PSP, interacted with specific binding sites in the gastrointestinal tract and inhibited the adenylate cyclase activity in rat intestinal mucosal cell membranes. The binding sites appeared to be heterogeneous and Scatchard analysis of the binding data indicated the presence of at least two classes of sites. The high-affinity low-capacity binding sites and the low-affinity high-capacity binding sites had apparent dissociation constants of 1.3 X 10(-7) mol/l and 4.2 X 10(-6) mol/l, respectively. The PSP induced inhibition of the adenylate cyclase activity was independent of the stimulatory state of the enzyme. The basal activity as well as that stimulated by VIP and secretin was half maximally inhibited at approximately 3 X 10(-5) mol/l of PSP. The inhibitory effect of PSP was independent of the agonist concentration employed. PSP did not affect the receptor binding of VIP nor did VIP affect the receptor binding of PSP.     

Induction of chromosomal aberrations in cultured Chinese hamster cells by short-term treatment with cadmium chloride

Inducibility of chromosomal aberrations and cytotoxicity in cultured Chinese hamster cells by cadmium chloride (CdCl2) was investigated under 3 different treatment conditions: (i) 2-h treatment in MEM medium supplemented with 10% fetal bovine serum (MEM + 10% FBS) or (ii) in HEPES-buffered Hanks' solution (HEPES-Hanks), and (iii) continuous treatment for 24 h in MEM + 10% FBS. Two-h treatment with CdCl2 in HEPES-Hanks or continuous treatment for 24 h in MEM + 10% FBS was respectively 2 or 3 times more cytotoxic than 2-h treatment with the metal in MEM + 10% FBS. Continuous treatment for 24 h with a CdCl2 concentration in excess of 5 X 10(-6) M was too toxic to the cells to allow chromosomal analysis, and moreover, only a slight increase in incidence of chromosomal aberrations was observed at a concentration of 5 X 10(-6) M CdCl2. In contrast, a marked and concentration-dependent increase in incidence of chromosomal aberrations was observed after post-treatment culture for 22 h follows 2-h treatment with 1 X 10(-6) M to 5 X 10(-5) M of CdCl2 in both MEM + 10% FBS and HEPES-Hanks. Two-h treatment with cadmium in HEPES-Hanks was approximately 3 times more potent for the induction of chromosomal aberrations than that in MEM + 10% FBS. Types of aberrations induced by CdCl2 mainly consisted of chromatid gaps and breaks, although a few exchanges, dicentrics and fragmentations were observed at high concentrations of cadmium. Increase in incidence of tetraploidy was also observed with a concentration dependency after 2-h treatment with CdCl2. Potency of CdCl2 to induce chromosomal aberrations after 2-h exposure was comparable to that of benzo[a]pyrene activated with S9 at equitoxic concentrations. Two-h treatment with cadmium markedly inhibited incorporation of [3H]thymidine, even at concentrations at which incorporation of [3H]uridine or [3H]leucine was less inhibited. However, the inhibition of [3H]thymidine incorporation by cadmium was reversible and the incorporation restored to the control level during 2-6 h of post-treatment incubation. These findings suggest that restoration of DNA synthesis after cadmium exposure is required for the efficient detection of chromosomal aberrations induced by the metal.     

Effects of cadmium treatment in vitro on the uptake and release of [3H]serotonin by human blood platelets

Effects of cadmium treatment on human platelets were studied with respect to uptake and release of 5-[3H]hydroxytryptamine (5-HT). The uptake of 5-[3H]HT in the presence of varying concentrations of CdCl2 (0.001-10 mM) was inhibited significantly with respect to control platelets and the inhibition was maximum at 1 mM CdCl2 concentration. From studies on the kinetics of 5-[3H]HT uptake a higher Km and significantly lower Vmax for CdCl2-treated platelets were observed. CdCl2 stimulated spontaneous release but inhibited thrombin-induced release of 5-[3H]HT. Spontaneous release of 5-[3H]HT induced by CdCl2 was not significantly altered in the presence of externally available CaCl2 (1 mM).     

Cadmium blocks receptor-mediated Jak/STAT signaling in neurons by oxidative stress

Cadmium is an environmental contaminant producing numerous pathological effects including neurological disorders. The mechanisms through which cadmium produces neurotoxicities are not completely known. We found that divalent cadmium (CdCl2) inhibited ciliary neurotrophic factor (CNTF)-mediated Jak1 and Jak2 tyrosine kinase signaling in human BE(2)-C neuroblastoma cells. CdCl2 concentrations as low as 0.1 microM and for times as brief as 2 h significantly reduced CNTF-induced tyrosine phosphorylation of both STAT1 and STAT3, the principle substrates of Jak kinases in neurons. The phosphorylation of STAT1 by interferon-gamma was also inhibited by CdCl2. However, activation of the fibroblast growth factor receptor tyrosine kinase was not inhibited by CdCl2. Jak/STAT signaling was inhibited by CdCl2 selectively in cultures of chick retina neurons and neuroblastoma cells, whereas signaling in the nonneuronal cells HepG2 and chick skeletal myotubes was not affected. Results using dichlorofluorescein indicated CdCl2 increased cellular oxidative stress, and all of these effects of CdCl2 were protected against by pretreatment with antioxidants. Neuronal inhibition of Jak kinase by CdCl2-induced oxidative stress is a new mechanism of cadmium action which may directly produce neurotoxic symptoms as well as implicate cadmium and related metals as environmental factors in the etiology of neurodegenerative diseases.     

Interaction of calf intestinal alkaline phosphatase with 8-anilinonaphthalene-1-sulphonate

Calf intestinal alkaline phosphatase is inhibited by 8-anilinonaphthalene-1-sulphonate (ANS). The inhibition is uncompetitive but non-linear. Hill plots of the inhibition data have slopes of 1.4-1.8 suggestive of positive cooperativity. Fluorescence titration revealed that 2 molecules of ANS bind per molecule of enzyme with no evidence of cooperativity. The Kd for ANS obtained by fluorescence was 1.8 X 10(-6) mol/l but the approximate Ki for inhibition was 1 X 10(-3) mol/l. Thus, the fluorescence and kinetic experiments appear to monitor different events.     

Enhancement of rat intestinal calcium absorption by vanadate.

Vanadate alters intestinal transport and may have a role in regulating cell function. To determine whether it influences calcium absorption, we tested the effects of acute and chronic vanadate administration on calcium absorption using single-pass perfusion of jejunal and ileal segments of the in vivo rat intestine. Acute vanadate administration increased the lumen-to-mucosa and net fluxes of calcium in both the jejunum and ileum. The increase was largely due to an enhancement of the saturable fluxes of calcium and was observed at 10(-4) M concentration of vanadate, but not at higher or lower concentrations of the oxyanion, except at the highest concentration used, 10(-2) M, where calcium absorption was inhibited. Chronic vanadate administration caused, on the other hand, no changes in calcium absorption. We have demonstrated previously that rat intestinal (Na+ + K+)-ATPase is inhibited by vanadate, an effect that could raise cell sodium and increase the efflux of sodium across the brush border membrane. The results suggest that the vanadate enhancement of calcium absorption may be related to an increased entry of calcium into the mucosa, possibly as a result of an augmented exchange through the Na+/Ca+ antiport system. Alternatively, vanadate may influence access to a calcium channel in the mucosal membrane of the intestinal epithelium, leading to the observed increase in absorption.     

Cadmium-dependent enzyme activity alteration is not imputable to lipid peroxidation

The effect of cadmium on the liver-specific activities of NADPH-cytochrome P450 reductase (CPR), malic dehydrogenase (MDH), glyceraldehyde-3-phosphate dehydrogenase (GADPH), and sorbitol dehydrogenase (SDH) was assessed 6, 24, and 48 h after administration of the metal to rats (2.5 mg/kg of body weight, as CdCl2, single ip injection). CPR specific activity increased after 6 h and afterward decreased significantly, while MDH specific activity increased up to 24 h and then remained unchanged. Both SDH and GADPH specific activities reduced after 6 h, the former only a little but the latter much more, and after 24 and 48 h were strongly inhibited. In vitro experiments, by incubating rat liver microsomes, mitochondria, or cytosol with CdCl2 in the pH range 6.0-8.0, excluded cadmium-induced lipid peroxidation as the cause of the reduction in enzyme activity. In addition, from these experiments, we obtained indications on the type of interactions between cadmium and the enzymes studied. In the case of CPR, the inhibitory effect is probably due to Cd2+ binding to the histidine residue of the apoenzyme, which, at physiological pH, acts as a nucleophilic group. In vitro, mitochondrial MDH was not significantly affected by cadmium at any pH, indicating that this enzyme is probably not involved in the decrease in mitochondrial respiration caused by this metal. As for GADPH specific activity, its inhibition at pH 7.4 and above is imputable to the binding of cadmium to the SH groups present in the enzyme active site, since in the presence of dithiothreitol this inhibition was removed. SDH was subjected to a dual effect when cytosol was exposed to cadmium. At pH 6.0 and 6.5, its activity was strongly stimulated up to 75 microM CdCl2 while at higher metal concentrations it was reduced. At pH 7.4 and 8.0, a stimulation up to 50 microM CdCl2 occurred but above this concentration, a reduction was found. These data seem to indicate that cadmium can bind to different enzyme sites. One, at low cadmium concentration, stimulates the SDH activity while the other, at higher metal concentrations, substitutes for zinc, thus causing inhibition. This last possibility seems to occur in vivo essentially at least 24 h after intoxication. The cadmium-induced alterations of the investigated enzymes are discussed in terms of the metabolic disorders produced which are responsible for several pathological conditions.     

Purification and properties of carotene 15,15'-dioxygenase of rabbit intestine

Carotene 15,15'-dioxygenase, which oxidizes carotenoids to retinal, has been purified up to 200-fold from rabbit intestine by ammonium sulfate fractionation, heat treatment, and acetone precipitation. With beta-apo-10'-carotenol as the substrate, the purified enzyme has a pH optimum of 7.8, a K(m) of 6.7 x 10(-5) m, and a V(max) at 37 degrees C of 9 nmoles of retinal/mg protein/hr. The purified enzyme is inhibited by ferrous ion-chelating agents such as alpha,alpha'-dipyridyl and o-phenanthroline, and by sulfhydryl-binding agents such as iodoacetamide, N-ethylmaleimide, and p-chloromercuribenzoate. The latter inhibitory effects are reversed by reduced glutathione. The cleavage of beta-apo-10'-carotenol is competitively inhibited by its acetylenic analog, 15,15'-dehydro-beta-apo-10'-carotenol. The enzyme is present in the intestinal mucosa of several mammals, the chicken, the tortoise, and a freshwater fish, but it is absent from cat intestinal tissue.     

Changes in NO bioavailability regulate cardiac O2 consumption: control by intramitochondrial SOD2 and intracellular myoglobin

The aim of this study was to investigate the significance of two intracellular scavengers of nitric oxide (NO): 1) superoxide dismutase (SOD) (SOD2) to scavenge intramitochondrial superoxide anion, and 2) cytosolic myoglobin (Mb) in the regulation of tissue O2 consumption. O2 consumption was measured in vitro using a Clark-type O2 electrode. SOD heterozygous mice (SODHZ) (n = 13) and SOD wild-type (SODWT) (n = 5) mice were used. Bradykinin (BK, 10-4 mol/l) reduced O2 consumption by 15% +/- 1 in hearts of SODHZ mice, which was significantly different from SODWT (reduced by 24 +/- 0.4%). Tiron significantly increased the inhibition of O2 consumption by BK in male mice from 15 +/- 1% (n = 13) to 29 +/- 1.2% (n = 4) at 10-4 mol/l concentration (P < 0.05). The effect of carbachol was similar to BK. S-nitroso-N-acetyl penicillamine (SNAP, 10-4 mol/l) reduced O2 consumption by 39 +/- 1.3% in hearts of SODHZ mice, which was not significantly different from SODWT. But at 10-7 mol/l, SNAP caused significantly less inhibition of O2 consumption in SODHZ mice. Mb knockout (MbKO; Mb wild-type n = 6) and (MbWT) mice (n = 6) were also used. Kidney cortex was studied as the negative control because it does not contain Mb. BK (10-4 mol/l) reduced O2 consumption by 32 +/- 2, 29 +/- 1, and 26 +/- 1% in the heart, skeletal muscle, and kidney of MbKO mice, which was also not significantly different from MbWT. SNAP (10-4 mol/l) reduced O2 consumption by 39 +/- 3, 42 +/- 4, and 46 +/- 2% in the heart, skeletal muscle, and kidney of MbKO mice, which was also not significantly different from MbWT. NG-nitro-l-arginine methyl ester (P < 0.05) inhibited the reduction in O2 consumption induced by BK in the MbKO mouse heart (15 +/- 1%), skeletal muscle (17 +/- 1%), and kidney (17 +/- 1%) as in the MbWT mice. These results suggest that the role of Mb as an intracellular NO scavenger is small, and the increase in mitochondrial superoxide in SODHZ mice may cause a decrease NO bioavailability and alter the control of myocardial O2 consumption by NO.     

Cadmium-bound metallothionein induces apoptosis in rat kidneys, but not in cultured kidney LLC-PK1 cells

The ability of cadmium-bound metallothionein(Cd-MT) to induce apoptosis was investigated in vivo and in vitro. Administration of purified Cd-MT (0.15 mg MT bound Cd per kg body weight) to the rat induces DNA fragmentation, a biochemical characteristic of apoptosis in the kidney at 16 h, which was detectable by ethidium bromide staining on an agarose gel. It was still detected 24 h after administration. Induction of apoptosis by Cd-MT was specific to kidney; it was not observed in cerebrum, cerebellum, heart, lung, liver, testis, dorsolateral prostate, and ventral prostate. In contrast, addition of Cd-MT (0.01-100 microM) to the cultured porcine kidney LLC-PK1 cells failed to induce apoptosis under the condition where cadmium chloride (10 microM) did. There was no additivity of induction of apoptosis by CdCl2 (10 microM) in the presence of Cd-MT (0.01-100 microM). To examine the effect of intracellular MT on cadmium-induced apoptosis in cultured cells, new cell lines were established, which constitutively produce MT, being termed as Cd(r)-LLC-PK1 cells since Cd-MT exogenously added had much less permeability to the cultured cells. Followed by exposure of wild-type LLC-PK1 cells to 50 microM CdCl2 for 24 h, the surviving cells(Cd(r)-LLC-PK1 cells) induce MT at the level of 1.9 microg/2 x 10(6) cells. In Cd(r)-LLC-PK1 cells, 10 microM CdCl2 failed to induce apoptosis, but 60 microM CdCl2 could exert the apoptotic response, indicating that intracellular MT which was induced by CdCl2 did not facilitate CdCl2-elicited apoptosis. Furthermore, chromatin in rat kidneys was condensed by Cd-MT, but not that in LLC-PK1 cells. Thus, Cd-MT induces apoptosis in rat kidneys, but not in the cultured renal cells, suggesting that the ionic form of cadmium was required for programmed cell death.     

Effect of aldosterone antagonists on aldosterone-induced activation of Mg2+ -HCO3- -ATPase and carbonic anhydrase in rat intestinal mucosa

In previous studies, Mg2+ -dependent, HCO3- -activated ATPase in the brush border and carbonic anhydrase in the cytoplasm of rat duodenal and jejunal mucosa decreased after adrenalectomy. Both enzyme activities increased to near normal levels 4 h after i.p. injection of aldosterone (40 micrograms/kg). These results suggest the possibility that both enzymes in the small intestinal mucosa may be mediators of the action of aldosterone. In the present studies, therefore, the effects of actinomycin D (500 micrograms/kg, i.p.), spironolactone (50 mg/kg, s.c.) and potassium canrenoate (50 mg/kg, s.c.) on aldosterone-induced activation of both enzymes in the upper small intestinal mucosa from adrenalectomized rats were examined to clarify the mechanism of action of aldosterone in enzyme levels. Actinomycin D inhibited carbonic anhydrase activity in small intestinal mucosa from normal rats 4 h after i.p. injection but had no effect on ATPase activity, while two other drugs had no effect on either enzyme activity in normal rats up to 4 h later. Pretreatment with these 3 drugs 1 h before aldosterone administration (40 micrograms/kg, i.p.) to adrenalectomized rats blocked the aldosterone-induced activation of ATPase and carbonic anhydrase in the upper small intestine. On the other hand, adrenalectomy and administration of aldosterone and its antagonists, alone or in combination, had no effect on kidney enzyme activities. These results confirm that Mg2+ -HCO3- -ATPase and carbonic anhydrase are mediators of the action of aldosterone in the upper small intestinal mucosa.     

Both endothelium and afferent nerve endings play a role in acetylcholine-induced renal vasodilation

We investigated the nature and signaling pathways of endothelium- and sensory-nerve ending-derived substances involved in acetylcholine-induced vasodilation in rat isolated perfused kidney. Endothelial denudation by Triton X-100 (0.2%, 0.1 ml) or depletion of afferent nerve endings by capsaicin (10(-6) mol/l) attenuated acetylcholine-induced vasodilation. When these two agents were administered together, the response to acetylcholine was completely inhibited. CGRP1 receptor blocker CGRP 8-37 (10(-7) mol/l) and adenosine A(2) receptor antagonist ZM 241 385 (10(-7) mol/l) inhibited acetylcholine-induced dilation. When indomethacin (10(-5) mol/l), a cyclooxygenase inhibitor, l-NOARG (10(-4) mol/l), a nitric oxide (NO) synthase inhibitor, and potassium chloride (30 mmol/l), to test EDHF response, were perfused simultaneously, the inhibition was greater than that was observed with each agent alone. Guanylate cyclase inhibitor ODQ (10(-5) mol/l) or protein kinase A inhibitor KT 5720 (5x10(-7) mol/l) inhibited acetylcholine-induced dilation. Gap junction uncoupler 18alpha-glycyrrhetinic acid (10(-4) mol/l) caused an uncontrollable increase in basal perfusion pressure making it impossible to test against acetylcholine-induced dilation. Our data suggest that NO, prostanoids, EDHF, and CGRP released from vascular endothelium and afferent nerve endings participate in acetylcholine-induced vasodilation and their signal transduction molecules include protein kinase A and guanylate cyclase.     

Identification of tyrosylprotein sulfotransferase in rat gastric mucosa.

An enzyme activity which catalyzes the transfer of the sulfate group from 3'-phosphoadenosine 5'-phosphosulfate (PAPS) to poly-Glu6,Ala3,Tyr1 (EAY; M(r) 47,000) has been demonstrated in the antral and body mucosa of the rat stomach. The distribution of this tyrosylprotein sulfotransferase was similar to that of the Golgi marker enzyme, glycoprotein sulfotransferase, and its activity from body mucosa was 23% higher than that from the antrum. The optimum for tyrosylprotein sulfotransferase activity was obtained at pH 6.8, in the presence of 0.5% Triton X-100, 20 mmol/l MnCl2, 50 mmol/l NaF, 2 mmol/l 5'-AMP, and 1 mmol/l DTT, whereas Ca2+, Mg2+, Cu2+, Zn2+, EDTA, NEM, NaCl and Na2SO4 were inhibitory. The apparent Km of the sulfotransferase for EAY was 1.5 x 10(-6) mol/l and for PAPS 0.75 x 10(-6) mol/l. The enzyme was 28 times less susceptible to 2,6-dichloro-4-nitrophenol inhibition as compared to that required for phenol sulfotransferase inhibition. The tyrosine sulfation by the tyrosylprotein sulfotransferase was independent of the sulfation of carbohydrate residues in mucous glycoproteins and glycolipids, thus indicating that the identified sulfotransferase is specific for sulfation of the tyrosyl residues in the peptide core.     

Nitric oxide reduces energy supply by direct action on the respiratory chain in isolated cardiomyocytes

To investigate the effect of nitric oxide (NO) on cardiac energy metabolism, isolated cardiomyocytes of Wistar rats were incubated in an Oxystat system at a constant ambient PO2 (25 mmHg) and oxygen consumption (VO2); free intracellular Ca(2+) (fura 2), free cytosolic adenosine [S-adenosylhomocysteine (SAH) method], and mitochondrial NADH (autofluorescence) were measured after application of the NO donor morpholinosydnonimine (SIN-1). In Na(+)-free medium (contracting cardiomyocytes), VO2 increased from 7.9 +/- 1.2 to 26.4 +/- 3.1 nmol x min(-1) x mg protein(-1). SIN-1 (100 micromol/l) decreased VO2 in contracting (-21 +/- 3%) and in quiescent cells (-24 +/- 7%) by the same extent. Inhibition of VO2 was dose dependent (EC(50): 10(-7) mol/l). S-nitroso-N-acetyl-penicillamine, another NO donor, also inhibited VO2, whereas SIN-1C (100 micromol/l), the degradation product of SIN-1, displayed no inhibitory effect. Intracellular Ca(2+) remained unchanged, and inhibition of protein kinases G, A, or C did not antagonize the effect of NO. Mitochondrial NADH increased with NO, indicating a reduced flux through the respiratory chain. In quiescent but not in contracting cardiomyocytes, NO significantly increased adenosine, indicating a reduced energy status. These data suggest the following. 1) NO decreases cardiac respiration, most likely via direct inhibition of the respiratory chain. 2) Whereas in quiescent cardiomyocytes the inhibition of aerobic ATP formation by NO causes reduction in energy status, contracting cells are able to compensate for the NO-induced inhibition of oxidative phosphorylation, maintaining energy status constant.     

An electron microscopic study of endogenous very low density lipoprotein production in the intestine of rat and man

Previous studies have shown that in the absence of dietary lipid, intestinal lymph contains endogenous very low density lipoproteins (VLDL) which are identical to those in plasma in size, flotation rate, composition, and electrophoretic mobility. In order to document that these particles are produced in the mucosa of the small intestine itself, electron microscopic studies of rat and human intestinal mucosa were carried out. Small intestinal absorptive cells from rats fasted and restrained for 48 hr were rich in osmiophilic particles of the size of VLDL (300-1000 A). These particles were present in the endoplasmic reticulum and Golgi apparatus, and in intercellular spaces and lacteals; they were most abundant in mucosa from mid-jejunum. Similar particles were seen in jejunal mucosal biopsy specimens obtained from normal human volunteers after a 40-hr fast. After 6 hr of bile diversion or cholestyramine administration to fasted rats, the VLDL-sized particles virtually disappeared from the mucosa, suggesting that they were produced in the mucosa itself and depended upon the absorption of endogenous intralumenal lipid. These studies provide further evidence for the production of VLDL in absorptive cells of fasting rat and human intestine, and support the concept that the small intestine is a source of endogenous plasma VLDL.     

Protective effects of N-acetylcysteine on intestinal functions of piglets challenged with lipopolysaccharide

The neonatal small intestine is susceptible to damage by endotoxin, but effective methods for prevention and treatment are lacking. N-acetylcysteine (NAC) is a widely used precursor of L: -cysteine for animal cells and plays an important role in protecting cells against oxidative stress. This study was conducted with the lipopolysaccharide (LPS)-challenged piglet model to determine the effects of NAC on intestinal function. Eighteen piglets were randomly allocated into control, LPS and LPS?+?NAC groups. The control and LPS groups were fed a corn- and soybean meal-based diet, and the LPS?+?NAC group was fed the basal diet +500?mg/kg NAC. On days 10, 13 and 20 of the trial, the LPS and LPS?+?NAC groups received intraperitoneal administration of LPS (100?μg/kg BW), whereas the control piglets received saline. On day 20 of the trial, D-: xylose (0.1?g/kg BW) was orally administrated to all piglets 2?h after LPS or saline injection, and blood samples were collected 1?h thereafter. One hour blood xylose test was used to measure intestinal absorption capacity and mucosal integrity, and diamine oxidase (DAO) was used as a marker of intestinal injury. On day 21 of the trial, pigs were killed to obtain the intestinal mucosa. Compared to the control, LPS challenge reduced (P?相似文献   

Inhibition of the mutagenic activity of some heterocyclic dietary carcinogens and other mutagenic/carcinogenic compounds by rat organ preparations

The mutagenic activity of some dietary mutagens, 2-amino-3-methylimidazo[4,5-f]quinoline (IQ), 2-amino-6-methyldipyrido[1,2-a:3',2'-d]imidazole (Glu-P-1) and 2-amino-dipyrido[1,2-a:3',2'-d]imidazole (Glu-P-2), was inhibited in the Salmonella-plate test preincubated with heat-inactivated rat intestinal preparations. A similar inhibition was observed by preincubating intestinal preparations with 2-acetylaminofluorene (AAF) and benzo[a]pyrene (B[a]P). The effect was not specific for small intestine and was also obtained with spleen, liver, lung, colon and stomach preparations. Mutagenic activity was not inhibited by beef muscle proteins. Lipids extracted from intestinal mucosa preparations were equally effective as inhibitors of the mutagenic activity. Lipid fractions from intestinal mucosa were capable of inhibiting the formation of activated IQ by mammalian S9, and other components of the intestinal preparations were able to bind the promutagens and their active metabolites. The mutagenic activity of 1-(2-hydroxyethyl)-2-methyl-5-nitroimidazole (metronidazole) and of N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) was also inhibited by intestinal preparations, but not by their lipid fractions. A binding of IQ to intestinal preparations was also demonstrated with HPLC techniques. The data indicate that tissue components may reduce the mutagenic activity of chemicals by interfering with the activation process and by reducing the concentration of the promutagens and their active metabolites at target sites.