Ischemia of rat stomach mobilizes ECL cell histamine

Effects of Platycodin D on Reflux Esophagitis due to Modulation of Antioxidant Defense Systems

Aims

The effects of platycodin D (PD) pretreatment were examined in reflux esophagitis (RE) induced rats.

Methods

Sham, control, and omeprazole (OMP) group were pretreated with distilled water or OMP as a reference, respectively, and PD pretreated groups were given 3 different PD doses once a day for 7 days. One hour after last pretreatment, RE was induced by ligation of the forestomach and pylorus. At 8 h after operation, all animals were sacrificed.

Results

PD showed significant dose-dependent reduction of gastric secretion, myeloperoxidase activity, and RE lesion areas of esophagus and stomach mucosa. There was a reduction of lipid peroxidation in 2 doses of PD groups and elevation of antioxidant enzyme activity in all PD groups. Gastric hexose and sialic acid were significantly increased in PD groups, while collagen was reduced. Plasma histamine levels were significantly reduced in all PD groups, but not in the OMP group. Total invasive lesion sizes of esophagus and gastric fundus were significantly decreased in all PD groups. Thicknesses in esophagus of all PD groups were significantly decreased and thicknesses of funds were significantly increased except lowest PD dose.

Conclusions

Therapeutic effects of PD on the esophageal and gastric lesions were shown in RE induced rats dose-dependently. The PD pretreatment had significant antioxidant effects with regulation of histamine levels. This study provides useful information regarding the effectiveness of the drug for RE and further novel drug discovery using natural herbal products.

Flavonoids from whole Plant of Euphorbia hirta and their Evaluation against Experimentally induced Gastroesophageal Reflux Disease in Rats

BACKGROUND

Euphorbia hirta possesses antibacterial, anti-inflammatory, galactogenic, antidiarrheal, antioxidant, hypoglycemic, antiasthmatic, antiamebic, antifungal, and antimalarial activities.

OBJECTIVE

The overall objective of the current study was the investigation of the whole plant extract of E. hirta and flavonoids from E. hirta on gastroesophageal reflux disease (GERD) in rats.

MATERIALS AND METHODS

The whole plant extract of E. hirta was characterized by analysis of flavonoids (HPLC: HPLC, UV, IR, MS and ¹HNMR). GERD model was induced surgically in Wistar rats under pentobarbitone sodium anesthesia (50 mg/kg, i.p.) and the tissue esophagus and stomach were removed. The tissues were washed with physiological saline and were examined for GERD. The whole plant extract of E. hirta in doses of 50, 100, and 200 mg/kg were administered orally twice daily at 10:00 and 16:00 hours, respectively, for 5 days and kaempferol (100 mg/kg) or omeprazole (OMZ) in the dose of 30 mg/kg 1 hour prior to the induction of GERD. Control groups received suspension of 1% carboxymethyl cellulose in distilled water (10 mL/kg).

RESULTS

The levels of gastric wall mucus increased and of plasma histamine and H⁺, K⁺ ATPase significantly decreased in groups treated by both the plant extract and flavonoids. Both the plant extract and flavonoids reduced the lipid peroxidation and superoxide dismutase and increased the levels of catalase and reduced glutathione.

CONCLUSIONS

The whole plant extract of E. hirta is attributed to its antisecretory, gastroprotective, and antioxidant potential as that of quercetin, rutin, kaempferol, and proton pump blocker (omeprazole) to treat GERD.

SUMMARY

The aqueous extract of whole plant of Euphorbia hirta revealed the presence of kaempferol (0.0256%), quercetin (0.0557%), and rutin (0.0151%), and the ethyl acetate fraction of whole plant of E. hirta possesses kaempferol (0.0487%), quercetin (0.0789%), and rutin (0.0184%).The levels of gastric wall mucus increased and of plasma histamine and H⁺-K⁺-ATPase significantly decreased in rats groups treated by both the whole plant extract of E. hirta and flavonoids.Both the whole plant extract of E. hirta and flavonoids reduced the lipid peroxidation and superoxide dismutase and increased the levels of catalase and reduced glutathione in rats groups. Abbreviation used: 1HNMR: Proton Nuclear Magnetic Resonance Spectroscopy, CAT: Catalase, EHAE: Aqueous extract of Euphorbia hirta, EHEF: Ethyl Acetate Fractions of Euphorbia hirta, GERD: Gastroesophageal reflux disease, GSH: Reduced Glutathione, HPLC: High performance liquid chromatography, IR: Infrared spectroscopy, LPO: Lipid Peroxidase, MDA: Malondialdehyde, MS: Mass Spectroscopy, OMZ: Omeprazole, ROS: Reactive Oxygen Species, SOD: Superoxide dismutase, TBHQ: tert-Butylhydroquinone, TLC: Thin Layer Chromatography, UV: Ultraviolet, UV: Ultraviolet-Visible Spectroscopy.

Gastric submucosal microdialysis in the detection of rat stomach ischemia--a comparison of the 3H2O efflux technique with metabolic monitoring

Microdialysis has been utilized for nutritive blood flow measurements, but both the advantages and disadvantages of various approaches have not been evaluated in parallel in the stomach yet. Our aim was to compare the (3)H(2)O efflux technique with biochemical monitoring during temporary celiac artery occlusion in anesthetized rats. Microdialysis probes were implanted in the gastric submucosa and perfused with (3)H(2)O; samples were analyzed for β-activity, glucose, lactate, pyruvate and glycerol. Gastric mucosa and plasma were subjected to morphometry and analysis of myeloperoxidase, total thiols and lactatdehydrogenase. The most dramatic responses to ischemia were observed in lactate/pyruvate and lactate/glucose (%) ratios (6.1-9.3×, p < 0.0001); the changes in (3)H(2)O efflux and glycerol were less pronounced (1.1-1.7×, p < 0.0001 and < 0.01, respectively). (3)H(2)O efflux correlated best with the lactate/glucose ratio and glucose alone (r = 0.693 and -0.681, respectively, p < 0.0001). A correlation was also found between plasma lactatdehydrogenase and relative glycerol release (r = 0.600, p < 0.05). Myeloperoxidase, lactatdehydrogenase and histology score were increased by ischemia/reperfusion (0.06-0.12 nkat g(-1), p < 0.05, 0.26-0.44 nkat g(-1), p < 0.05 and 1.79-2.33, p < 0.05, respectively), macroscopy and plasma thiols remained unchanged. Microdialysis is useful in monitoring gastric ischemia, metabolic monitoring being superior to the (3)H(2)O efflux technique. The results question the efficacy of the utilized model to produce standardized major gastric damage.

Protective effect of (+)-catechin against gastric mucosal injury induced by ischaemia-reperfusion in rats

Ischaemia and reperfusion are known to induce gastric lesions, predominantly due to excessive formation of reactive oxygen metabolites, adhesion of neutrophils to endothelial cells, microvascular dysfunction, gastric acid secretion, endogenous histamine and gastrin release. We have studied the effect of (+)-catechin on a gastric ulcer model involving damage to gastric injury by ischaemia-reperfusion (I/R) in rats. (+)-Catechin 50 mg kg−1 administered orally, once daily for three days after the initiation of I/R injury showed a significant (P &lt; 0.001) anti-ulcer activity against mucosal damage. However, (+)-catechin significantly decreased the lipid peroxidation and increased the level of catalase in the I/R condition. Elevated levels of alkaline phosphatase in the I/R group was significantly lowered (P &lt; 0.01) by (+)-catechin. The amount of H+K+ATPase was significantly decreased (P &lt; 0.001) in (+)-catechin-treated as compared with I/R rats. (+)-Catechin significantly decreased elevated plasma histamine (P &lt; 0.05) and corticosterone (P &lt; 0.05). The results suggested that (+)-catechin protected gastric mucosa against ischaemia-reperfusion-induced gastric ulcers by its antioxidant activity and mucus protection.

Serum levels of gastric-acid-stimulating factors in children undergoing open heart surgery

PURPOSE

Upper gastrointestinal (GI) bleeding is a feared consequence of open heart surgery in children. Increased gastric acid secretion is a known key factor in the pathogenesis of gastritis and upper intestinal ulcerations. The aim of this study is to evaluate the serum kinetics of acid-stimulating factors and associated perioperative parameters after heart surgery in children.

METHODS

Fifteen pediatric patients after open heart surgery and 15 children with cardiac catheterization were included in this study. Serum levels of gastrin, histidine, alanine, and tryptophan were analyzed before and up to 26 h after surgery.

RESULTS

In the postoperative period there was a significant elevation of gastrin with a peak at 4 h after surgery. Serum histidine was increased significantly immediately after surgery only in patients undergoing heart surgery with cardioplegia. No association of gastrin and histidine elevation with ischemia, perfusion time or lactate was observed.

CONCLUSION

Factors that are responsible for postoperative gastrin elevation still have to be determined. Circumstances of extracorporeal circulation (ECC) in low-risk patients most likely do not lead to relevant elevation of amino acids with acid-stimulatory effect in our study population.

Multiphoton imaging of renal regulatory mechanisms

Most physiological functions of the kidneys, including the clearance of metabolic waste products, maintenance of body fluid, electrolyte homeostasis, and blood pressure, are achieved by complex interactions between multiple renal cell types and previously inaccessible structures in many organ parts that have been difficult to study. Multiphoton fluorescence microscopy offers a state-of-the-art imaging technique for deep optical sectioning of living tissues and organs with minimal deleterious effects. Dynamic regulatory processes and multiple functions in the intact kidney can be quantitatively visualized in real time, noninvasively, and with submicron resolution. This article reviews innovative multiphoton imaging technologies and their applications that provided the most complex, immediate, and dynamic portrayal of renal function-clearly depicting as well as analyzing the components and mechanisms involved in renal (patho)physiology.

The development of multiple probe microdialysis sampling in the stomach

A multiple probe approach of implanting microdialysis probes into each separate tissue layer would better represent sampling from the stomach. Presently, microdialysis sampling experiments are performed with only a single probe in the submucosa to represent sampling from the stomach tissue. The focus of this research was to develop a four-probe microdialysis sampling design to simultaneously monitor the stomach lumen, mucosa, submucosa and in the blood of the rat. Due to the small outer diameter of the microdialysis probe (350 microm), implantation into each separate layer was achieved with confirmation of probe location from histological examination. To assess the significance of sampling by this approach, multiple probe microdialysis sampling was used to monitor drug absorption in the stomach. Salicylic acid, caffeine and metoprolol were individually dosed to the ligated stomach. Analysis of the dialysate samples was performed by HPLC-UV and concentration-time curves and pharmacokinetics analysis were used to determine differences between the different probe locations.

The role of ICAM-1 in endotoxin-induced acute renal failure

The pathogenesis of acute renal failure (ARF) occurring during the course of sepsis is incompletely understood. Intercellular adhesion molecule-1 (ICAM-1) is a key cell adhesion molecule upregulated by LPS, which binds to the integrins CD11a/CD18 and CD11b/CD18 present on the surface of leukocytes. We hypothesized that ICAM-1 facilitates renal injury in LPS-induced ARF. To test this, three groups of mice (n = 8 per group) were injected intraperitoneally with 6 mg/kg LPS: 1) normal C57BL/6 mice, 2) mice with a targeted deficiency of ICAM-1 (ICAM-1(-/-)), and 3) mice expressing very low levels of CD18 (CD18-def). ICAM-1(-/-) mice were significantly resistant to LPS-mediated ARF, as opposed to CD18-def mice, which developed severe ARF, as did wild-type controls (48 h blood urea nitrogen 143 +/- 31.5, 70.8 +/- 24.4, and 185 +/- 16.6 mg/dl in wild-type, ICAM-1(-/-), and CD18-def mice, respectively, P < 0.05). At death, ICAM-1(-/-) mice had significantly less renal neutrophil infiltration than the other two groups, as well as less histological tubular injury. Depletion of neutrophils with mAb Gr-1 led to a profound exaggeration of tumor necrosis factor (TNF) release and high mortality, but neutrophil-depleted mice receiving 10-fold less LPS were protected against ARF despite TNF release similar to what is normally associated with LPS-induced ARF. LPS caused a significant increase in renal expression of chemokines; however, this increase was significantly exaggerated in CD18-def mice, which may account for their lack of protection. In conclusion, these data show that ICAM-1 plays a key role in LPS-induced ARF.

Fasting-induced changes in ECL cell gene expression

Gastric enterochromaffin-like (ECL) cells release histamine in response to food because of elevation of gastrin and neural release of pituitary adenylate cyclase-activating peptide (PACAP). Acid secretion is at a basal level in the absence of food but is rapidly stimulated with feeding. Rats fasted for 24 h showed a significant decrease of mucosal histamine despite steady-state expression of the histamine-synthesizing enzyme histidine decarboxylase (HDC). Comparative transcriptomal analysis using gene expression oligonucleotide microarrays of 95% pure ECL cells from fed and 24-h fasted rats, thereby eliminating mRNA contamination from other gastric mucosal cell types, identified significantly increased gene expression of the enzymes histidase and urocanase catabolizing the HDC substrate L-histidine but significantly decreased expression of the cellular L-histidine uptake transporter SN2 and of the vesicular monoamine transporter 2 (VMAT-2) responsible for histamine uptake into secretory vesicles. This was confirmed by reverse transcriptase-quantitative polymerase chain reaction of gastric fundic mucosal samples from fed and 24-h fasted rats. The decrease of VMAT-2 gene expression was also shown by a decrease in VMAT-2 protein content in protein extracts from fed and 24-h fasted rats compared with equal amounts of HDC protein and Na-K-ATPase alpha(1)-subunit protein content. These results indicate that rat gastric ECL cells regulate their histamine content during 24-h fasting not by a change in HDC gene or protein expression but by regulation of substrate concentration for HDC and a decreased histamine secretory pool.

Secretion of ghrelin from rat stomach ghrelin cells in response to local microinfusion of candidate messenger compounds: a microdialysis study

Ghrelin is produced by A-like cells (ghrelin cells) in the mucosa of the acid-producing part of the stomach. The mobilization of ghrelin is stimulated by nutritional deficiency and suppressed by nutritional abundance. In an attempt to identify neurotransmitters and regulatory peptides that may contribute to the physiological, nutrient-related regulation of ghrelin secretion, we challenged the ghrelin cells in situ with a wide variety of candidate messengers, including known neurotransmitters (e.g. acetylcholine, catecholamines), candidate neurotransmitters (e.g. neuropeptides), local tissue hormones (e.g. serotonin, histamine, bradykinin, endothelin), circulating gut hormones (e.g. gastrin, CCK, GIP, neurotensin, PYY, secretin) and other circulating hormones/regulatory peptides (e.g. calcitonin, glucagon, insulin, PTH). Microdialysis probes were placed in the submucosa of the acid-producing part of the rat stomach. Three days later, the putative messenger compounds were administered via the microdialysis probe (reverse microdialysis) at a screening dose of 0.1 mmol l(-1) for regulatory peptides and 0.1 and 1 mmol l(-1) for amines and amino acids. The rats were awake during the experiments. The resulting microdialysate ghrelin concentration was monitored continuously for 3 h (radioimmunoassay), thereby revealing stimulators or inhibitors of ghrelin secretion. Dose-response curves were constructed for each candidate messenger that significantly (p<0.05) affected ghrelin mobilization at the screening dose. Peptides that showed a (non-significant) tendency to affect ghrelin release at the screening dose were also given at a dose of 0.3 or 1 mmol l(-1). Adrenaline, noradrenaline, endothelin and secretin stimulated ghrelin release, while somatostatin and GRP inhibited. Whether these agents act directly or indirectly on the ghrelin cells remains to be investigated. All other candidate messengers were without measurable effects, including acetylcholine, serotonin, histamine, GABA, aspartic acid, glutamic acid, glycine, VIP, PACAP, CGRP, substance P, NPY, PYY, PP, gastrin, CCK, GIP, insulin, glucagon, GLP and glucose.

Microcirculation: nexus of comorbidities in diabetes

Generalized capillary dysfunction is a morbid element in the metabolic syndrome, and it is likely involved in its complications. We tested the hypothesis that vast amounts of serum albumin previously observed in kidneys of rats with the metabolic syndrome were caused, in part, by leakage from renal peritubular capillaries. We report herein large scale leaks of plasma fluid in peritubular capillaries of rats with the metabolic syndrome. This finding was directly demonstrated in vivo, and the presence of leftover albumin residue confirmed the leak in postmortem kidney specimens. Moreover, renal interstitial fibrosis and tubular atrophy were found in a distribution similar to the leaked renal albumin in obese rats. We suggest that there is an important link between peritubular capillary damage and interstitial fibrosis, represented as tubulointerstitial disease in the metabolic syndrome. We propose that maintenance of the peritubular microcirculation may improve renal outcomes in diabetes and the metabolic syndrome.

Activated protein C ameliorates LPS-induced acute kidney injury and downregulates renal INOS and angiotensin 2

Endothelial dysfunction contributes significantly to acute renal failure (ARF) during inflammatory diseases including septic shock. Previous studies have shown that activated protein C (APC) exhibits anti-inflammatory properties and modulates endothelial function. Therefore, we investigated the effect of APC on ARF in a rat model of endotoxemia. Rats subjected to lipopolysaccharide (LPS) treatment exhibited ARF as illustrated by markedly reduced peritubular capillary flow and increased serum blood urea nitrogen (BUN) levels. Using quantitative two-photon intravital microscopy, we observed that at 3 h post-LPS treatment, rat APC (0.1 mg/kg iv bolus) significantly improved peritubular capillary flow [288 +/- 15 microm/s (LPS) vs. 734 +/- 59 microm/s (LPS+APC), P = 0.0009, n = 6], and reduced leukocyte adhesion (P = 0.003) and rolling (P = 0.01) compared with the LPS-treated group. Additional experiments demonstrated that APC treatment significantly improved renal blood flow and reduced serum BUN levels compared with 24-h post-LPS treatment. Biochemical analysis revealed that APC downregulated inducible nitric oxide synthase (iNOS) mRNA levels and NO by-products in the kidney. In addition, APC modulated the renin-angiotensin system by reducing mRNA expression levels of angiotensin-converting enzyme-1 (ACE1), angiotensinogen, and increasing ACE2 mRNA levels in the kidney. Furthermore, APC significantly reduced ANG II levels in the kidney compared with the LPS-treated group. Taken together, these data suggest that APC can suppress LPS-induced ARF by modulating factors involved in vascular inflammation, including downregulation of renal iNOS and ANG II systems. Furthermore, the data suggest a potential therapeutic role for APC in the treatment of ARF.

Rapid determination of renal filtration function using an optical ratiometric imaging approach

Glomerular filtration rate (GFR), which measures the amount of plasma filtered through the kidney within a given time, is an essential and clinically important indicator of kidney function. Here, we report a new ratiometric measurement technique based on intravital fluorescence microscopy that allows rapid evaluations of renal function in rodent models. By using this technique, plasma clearance rates of a fluorescent GFR marker can be measured in less than 5 min following a bolus infusion of a fluorescent dye mixture into the bloodstream. The plasma clearance kinetics of the GFR marker showed consistent values when measured in healthy animals at locations both in the kidney and from the skin. In addition, by using this technique, we were able to rapidly determine renal function with acute renal failure animal models and with other animal models where kidney filtration functions were altered. The measured plasma clearance kinetics using this technique correlated with expected changes in kidney function. We found this ratiometric approach offers improved accuracy and speed for quantifying renal function compared with the approach using single fluorescent probes, and the measurement can be done noninvasively from the skin. This approach also offers a high sensitivity for determining plasma clearance rate of a fluorescent compound. This feature is important for rapidly quantifying small differences in plasma clearance when kidney function is changing.

Fluid flow in the juxtaglomerular interstitium visualized in vivo

Earlier electron microscopy studies demonstrated morphological signs of fluid flow in the juxtaglomerular apparatus (JGA), including fenestrations of the afferent arteriole (AA) endothelium facing renin granular cells. We aimed to directly visualize fluid flow in the JGA, the putative function of the fenestrated endothelium, using intravital multiphoton microscopy of Munich-Wistar rats and C57BL6 mice. Renin content of the AA correlated strongly with the length of the fenestrated, filtering AA segment. Fluorescence of the extracellular fluid marker lucifer yellow (LY) injected into the cannulated femoral vein in bolus was followed in the renal cortex by real-time imaging. LY was detected in the interstitium around the JG AA before the plasma LY filtered into Bowman's capsule and early proximal tubule. The fluorescence intensity of LY in the JGA interstitium was 17.9 ± 3.5% of that in the AA plasma ( n = 6). The JGA fluid flow was oscillatory, consisting of two components: a fast (one every 5–10 s) and a slow (one every 45–50 s) oscillation, most likely due to the rapid transmission of both the myogenic and tubuloglomerular feedback (TGF)-mediated hemodynamic changes. LY was also detected in the distal tubular lumen about 2–5 s later than in the AA, indicating the flow of JGA interstitial fluid through the macula densa. In the isolated microperfused JGA, blocking the early proximal tubule with a micropipette caused significant increases in MD cell volume by 62 ± 4% ( n = 4) and induced dilation of the intercellular lateral spaces. In summary, significant and dynamic fluid flow exists in the JGA which may help filter the released renin into the renal interstitium (endocrine function). It may also modulate TGF and renin signals in the JGA (hemodynamic function).

Quantitative imaging of basic functions in renal (patho)physiology

Multiphoton fluorescence microscopy offers the advantages of deep optical sectioning of living tissue with minimal phototoxicity and high optical resolution. More importantly, dynamic processes and multiple functions of an intact organ can be visualized in real time using noninvasive methods, and quantified. These studies aimed to extend existing methods of multiphoton fluorescence imaging to directly observe and quantify basic physiological parameters of the kidney including glomerular filtration rate (GFR) and permeability, blood flow, urinary concentration/dilution, renin content and release, as well as more integrated and complex functions like the tubuloglomerular feedback (TGF)-mediated oscillations in glomerular filtration and tubular flow. Streptozotocin-induced diabetes significantly increased single-nephron GFR (SNGFR) from 32.4 +/- 0.4 to 59.5 +/- 2.5 nl/min and glomerular permeability to a 70-kDa fluorophore approximately eightfold. The loop diuretic furosemide 2-fold diluted and increased approximately 10-fold the volume of distal tubular fluid, while also causing the release of 20% of juxtaglomerular renin content. Significantly higher speeds of individual red blood cells were measured in intraglomerular capillaries (16.7 +/- 0.4 mm/s) compared with peritubular vessels (4.7 +/- 0.2 mm/s). Regular periods of glomerular contraction-relaxation were observed, resulting in oscillations of filtration and tubular flow rate. Oscillations in proximal and distal tubular flow showed similar cycle times ( approximately 45 s) to glomerular filtration, with a delay of approximately 5-10 and 25-30 s, respectively. These innovative technologies provide the most complex, immediate, and dynamic portrayal of renal function, clearly depicting the components and mechanisms involved in normal physiology and pathophysiology.

Multiphoton imaging of renal tissues in vitro

The highly inhomogeneous and light-scattering structure of living renal tissue makes the application of conventional imaging techniques more difficult compared with other parenchymal organs. On the other hand, key physiological processes of the kidney, such as regulation of glomerular filtration, hemodynamics, concentration, and dilution, involve complex interactions between multiple cell types and otherwise inaccessible structures that necessitate visual approaches. An ideal solution is multiphoton excitation fluorescence microscopy, a state-of-the-art imaging technique superior for deep optical sectioning of living tissue samples. Here, we review the basics and advantages of multiphoton microscopy and provide examples for its application in renal physiology using dissected cortical and medullary tissues in vitro. In combination with microperfusion techniques, the major functions of the juxtaglomerular apparatus, tubuloglomerular feedback and renin release, can be studied with high spatial and temporal resolution. Salt-dependent changes in macula densa cell volume, vasoconstriction of the afferent arteriole, and activity of an intraglomerular precapillary sphincter composed of renin granular cells are visualized in real time. Release and tissue activity of renin can be studied on the individual granule level. Imaging of the living inner medulla shows how interstitial cells interconnect cells of the vasa recta, loop of Henle, and collecting duct. In summary, multiphoton microscopy is an exciting new optical sectioning technique that has great potential for numerous future developments and is ideal for applications that require deep optical sectioning of living tissue samples.