Fistula Rats Research Articles

Effects of Ya-hom on the gastric secretion in rats

The effects of Ya-hom, Thai traditional recipe, on gastric-secretory function was evaluated to verify its use for stomach discomfort treatment. The actions of Ya-hom on the gastric acid, pepsin and mucus secretions were studied in histamine- and carbachol-induced gastric fistula rats. After the first hour of collection, histamine (10 mg/kg, intramuscular injection) or carbachol (20 μg/kg, intravenous injection) were injected to stimulate gastric secretion, and water or redissolved lyophilized Ya-hom extract (0.5, 1, 2 and 4 g/kg) were intraduodenally injected. The gastric samples were collected every hour for 5 h, at the end of which, the glandular part of the stomach was assayed for the visible mucus content. Ya-hom inhibited both histamine- and carbachol-induced gastric acid, pepsin and soluble mucus secretions in a dose-dependent manner. Ya-hom had a lower maximum inhibition on the acid-stimulating effects of the histamine than that of carbachol. Ya-hom had higher maximum inhibition on the pepsin and soluble mucus-stimulating effects of histamine than that of carbachol. Ya-hom also had a higher elevated effect on histamine-induced visible mucus than that of carbachol. This study reveals that Ya-hom inhibits the stimulatory effects of histamine and carbachol on the acid, pepsin and soluble mucus secretion but potentiates the visible mucus secretion. Attenuating gastric secretion by secretagogues and increasing gastric barrier effects are parts of Ya-hom’s action on stomach discomfort treatment.

Angiographic, hemodynamic and histological characterization of an arteriovenous fistula in rats.

Our understanding of the pathogenesis of arteriovenous malformations (AVMs) and arteriovenous fistulas (AVFs) has been limited by the lack of adequate animal models. In this study we evaluate the time course of angiographic, hemodynamic and histopathological changes in an arteriovenous fistula in rats as a potential model. An arteriovenous fistula was created by a side-to-end anastomosis of the common carotid artery (CCA) to the external jugular vein (EJV). The animals underwent angiography of the fistula and were sacrificed 1, 7, 21, 42 or 90 days later. Flow and pressure measurements were performed in the CCA and ipsi- and contralateral EJV and detailed histological examination of whole mount sections of the fistula and cranium were done on fixed sections. Immunohistochemistry for CD31, smooth muscle alpha-actin and Ki-67 were performed. Hemodynamic changes occur immediately after fistula formation creating a stable high flow, low resistant state. This induces a gradual increase in the inner diameter of the EJV and transverse sinus followed by a decrease in size of the transverse sinus. This decrease is associated with increased expression of alpha-actin in the wall of the sinus. The fistula becomes angiographically and histologically stable after 21 days. This model describes the time course of hemodynamic and histopathological changes after occur after AVF formation. Stabilization after 21 days makes it an attractive model for mechanistic and therapeutic studies of AVFs.

Ghrelin stimulates gastric emptying but is without effect on acid secretion and gastric endocrine cells

Ghrelin, a recently discovered peptide hormone, is produced by endocrine cells in the stomach, the so-called A-like cells. Ghrelin binds to the growth hormone (GH) secretagogue receptor and releases GH. It is claimed to be orexigenic and to control gastric acid secretion and gastric motility. In this study, we examined the effects of ghrelin, des-Gln 14-ghrelin, des-octanoyl ghrelin, ghrelin-18, -10 and -5 (and motilin) on gastric emptying in mice and on gastric acid secretion in chronic fistula rats and pylorus-ligated rats. We also examined whether ghrelin affected the activity of the predominant gastric endocrine cell populations, G cells, ECL cells and D cells. Ghrelin and des-Gln 14-ghrelin stimulated gastric emptying in a dose-dependent manner while des-octanoyl ghrelin and motilin were without effect. The C-terminally truncated ghrelin fragments were effective but much less potent than ghrelin itself. Ghrelin, des-Gln 14-ghrelin and des-octanoyl ghrelin neither stimulated nor inhibited gastric acid secretion, and ghrelin, finally, did not affect secretion from either G cells, ECL cells or D cells.

Fluoxetine and sertraline stimulate gastric acid secretion via a vagal pathway in anaesthetised rats

The effect of the selective serotonin reuptake inhibitors, fluoxetine and sertraline on basal, secretagogues (histamine or bethanechol)- and distention-stimulated gastric acid secretion was investigated in the urethane-anaesthetised acute gastric fistula rat. Gastric acid secretion was measured by flushing of the gastric contents with saline every 15 min. Fluoxetine (10 or 20 mg kg −1, i.p.) produced a dose-dependent increase in basal gastric acid secretion. These stimulatory effects were abolished by vagotomy. Intraperitoneally administered sertraline also stimulated gastric acid secretion. The stimulatory effect of lower doses (5 mg kg −1) of sertraline was similar to that of the higher (30 mg kg −1) doses. The gastric secretory response to i.p. sertraline was long lasting (greater than 60 min), and blocked by vagotomy. Intraperitoneally administered fluoxetine (10 or 20 mg kg −1) or sertraline (5 mg kg −1) also increased gastric secretion induced by histamine, bethanechol or distention. The fluoxetine or sertraline stimulatory effects of histamine-induced acid secretion were abolished by vagotomy. Data indicate a stimulatory effect for fluoxetine and sertraline mediated by vagal nerve on gastric acid secretion in urethane-anaesthetised rats.

Physicochemical and physiological properties of 5α-cyprinol sulfate, the toxic bile salt of cyprinid fish

5alpha-Cyprinol sulfate was isolated from bile of the Asiatic carp, Cyprinus carpio. 5alpha-Cyprinol sulfate was surface active and formed micelles; its critical micellization concentration (CMC) in 0.15 M Na+ using the maximum bubble pressure device was 1.5 mM; by dye solubilization, its CMC was approximately 4 mM. At concentrations >1 mM, 5alpha-cyprinol sulfate solubilized monooleylglycerol efficiently (2.1 molecules per mol micellar bile salt). When infused intravenously into the anesthetized rat, 5alpha-cyprinol sulfate was hemolytic, cholestatic, and toxic. In the isolated rat liver, it underwent little biotransformation and was poorly transported (Tmax congruent with 0.5 micromol/min/kg) as compared with taurocholate. 5alpha-Cyprinol, its bile alcohol moiety, was oxidized to its corresponding C27 bile acid and to allocholic acid (the latter was then conjugated with taurine); these metabolites were efficiently transported. 5alpha-Cyprinol sulfate inhibited taurocholate uptake in COS-7 cells transfected with rat asbt, the apical bile salt transporter of the ileal enterocyte. 5alpha-Cyprinol had limited aqueous solubility (0.3 mM) and was poorly absorbed from the perfused rat jejunum or ileum. Sampling of carp intestinal content indicated that 5alpha-cyprinol sulfate was present at micellar concentrations, and that it did not undergo hydrolysis during intestinal transit. These studies indicate that 5alpha-cyprinol sulfate is an excellent digestive detergent and suggest that a micellar phase is present during digestion in cyprinid fish.

Drug delivery to the liver: A potential targeted therapy for hepatocellular carcinoma

Aim: Using the bile acid derivative cholyl lysine as a carrier to target cytotoxic drugs such as doxombicin and melphalan to the liver, the aim was to synthesise cholyllysyldoxorubicin (CLD) and cholyllysylmelphalan (CLM) in order to demonstrate (a) that their biological properties were simflar to the parent drugs, and Co) they were specifically targeted to the liver. Methods: The cytotoxicity in HepG2 cells was determined using either in situ end labelling or a lactate dehydrogenase assay. For the in vivo studies, bile fistula rats were injected via the jugular vein with ~4C-CLD, ~4C-CLM or ~4C-doxorubicin. Heart, liver, blood and urine samples were taken for radioactivity analysis. In another group of bile fistula rats, 17[3-estradiol glucuronide (1713-EG) was administered to induce cholestasis Rats were iolected via the jugular vein with I+C-CLM, followed by collection of bile, blood and liver samples for analysis of ~4C-CLM content. Results: The assessment of the cytotoxicity of CLD versus doxombicin and cholate indicated that doxombicin and CLD had similar cytotoxic aclivity. For example, 50% cell death was achieved at 0.45~tmol for both doxorubicin and CLD, but no effects were seen for cholate The cytotoxicity of CLM was equivalent to melphalan and doxorubicin, with some differences seen at low concentrations (melphalan being more toxic than CLM), and also at high concentrations (CLM being more toxic than melphalan). In bile fistula rats. cumulative bfliary excretion of ~4C-CLD was 81 _+ 4% per hoar, 13.5 + 06% per hour for doxorubicin, and 94_+2% per hour for ~4C-CLM Residual *C-doxombicin was 1.9 _+ 0.4% in liver, 10.8 +1% in heart, 74.9 _+ 9.6% in blood, and 40*0.8% in urine after one hour. Residual ~4C-CLD was 13.2_+4.3% in liver, 4.6_+3.2% in blood, and 2,0 _+ 0 5% in urine, with no detection in the heart after one hour. Residual +C-CLM was 10+_2% in liver, and 2.1 +_0.5% in blood, with no detection in heart and unne after one hour. In 1713-EG treated rats, cumulative biliary excretion of ~4C-CLM per boar was 28.8+_38%, with 37.0_+5.0% retained in the liver and 3.3+_0.9% in blood. Conclusion: These studies demonstrate that CLD and CLM maintain the cytotoxic potential 0[ the parent drugs but are clearly liver specific; thus avoiding potential dose-limiting sideeftects Further investigations into their potential use in the treatment of hepatocellular carcinoma are therefore warranted

Effects of curcumin on cyclosporine-induced cholestasis and hypercholesterolemia and on cyclosporine metabolism in the rat.

Former studies have shown that curcumin, which can be extracted from different Curcuma species, is able to stimulate bile flow and to reduce hypercholesterolemia. We investigated in a subchronic bile fistula model the ability of curcumin to reduce cyclosporine-induced cholestasis and hypercholesterolemia. Male Wistar rats were daily treated with curcumin (100 mg/kg p. o.), cyclosporine (10 mg/kg i. p.), and a combination of curcumin with cyclosporine. After two weeks a bile fistula was installed into the rats to measure bile flow and biliary excretion of bile salts, cholesterol, bilirubin, cyclosporine and its main metabolites. Blood was taken to determine the concentration of these parameters in serum or blood. Cyclosporine reduced bile flow (-14 %) and biliary excretion of bile salts (-10 %) and cholesterol (-61 %). On the other hand, cyclosporine increased serum concentrations of cholesterol and triglycerides by 32 % and 82 %, respectively. Sole administration of curcumin led to a slight decrease of bile flow (-7 %) and biliary bile salt excretion (-12 %), but showed no effect on biliary excretion of cholesterol and serum lipid concentration. When curcumin was given simultaneously with cyclosporine, the cyclosporine-induced cholestasis was enhanced but the cyclosporine-induced hyperlipidemia was not affected. Neither the biliary excretion nor the blood concentration of cyclosporine was influenced by curcumin. The blood concentration of the main cyclosporine metabolites, however, was lowered by half while their biliary excretion was strongly increased by curcumin. From these results we conclude that curcumin is not able to prevent cyclosporine-induced cholestasis and hyperlipidemia after prolonged administration in bile fistula rats.

Apoptosis in the left ventricle of chronic volume overload causes endocardial endothelial dysfunction in rats.

The hypothesis is that chronic increases in left ventricular (LV) load induce oxidative stress and latent matrix metalloproteinase (MMP) is activated, allowing the heart to dilate in the absence of endothelial nitric oxide (NO) and thereby reduce filling pressure. To create volume overload, an arteriovenous (A-V) fistula was placed in male Sprague-Dawley rats. To decrease oxidative stress and apoptosis, 0.08 mg/ml nicotinamide (Nic) was administered in drinking water 2 days before surgery. The rats were divided into the following groups: 1) A-V fistula, 2) A-V fistula + Nic, 3) sham operated, 4) sham + Nic, and 5) control (unoperated); n = 6 rats/group. After 4 wk, hemodynamic parameters were measured in anesthetized rats. The heart was removed and weighed, and LV tissue homogeneates were prepared. A-V fistula caused an increase in heart weight, lung weight, and end-diastolic pressure compared with the sham group. The levels of malondialdehyde (MDA; a marker of oxidative stress) was 6.60 +/- 0.23 ng/mg protein and NO was 6.87 +/- 1.21 nmol/l in the LV of A-V fistula rats by spectrophometry. Nic treatment increased NO to 13.88 +/- 2.5 nmol/l and decreased MDA to 3.54 +/- 0.34 ng/mg protein (P = 0.005). Zymographic levels of MMP-2 were increased, as were protein levels of nitrotyrosine and collagen fragments by Western blot analysis. The inhibition of oxidative stress by Nic decreased nitrotyrosine content and MMP activity. The levels of tissue inhibitor of metalloproteinase-4 mRNA were decreased in A-V fistula rats and increased in A-V fistula rats treated with Nic by Northern blot analysis. TdT-mediated dUTP nick-end labeling-positive cells were increased in A-V fistula rats and decreased in fistula rats treated with Nic. Acetylcholine and nitroprusside responses in cardiac rings prepared from the above groups of rats suggest impaired endothelial-dependent cardiac relaxation. Treatment with Nic improves cardiac relaxation. The results suggest that an increase in the oxidative stress and generation of nitrotyrosine are, in part, responsible for the activation of metalloproteinase and decreased endocardial endothelial function in chronic LV volume overload.

Octreotida no tratamento de fístulas entéricas de ratos

Somatostatina e seu análogo sintético octreotida são as drogas mais amplamente utilizadas para tratar fístulas enterocutâneas. Todavia, as evidências suportando seu uso ainda são insuficientes. Objetivo: Investigar os efeitos terapêuticos de octreotida em um modelo experimental de fístula enterocutânea. Métodos: Em trinta ratos machos Wistar com peso 210± 17g foi confeccionada cirurgicamente uma fístula jejunocutânea. Os animais foram aleatoriamente divididos em três grupos de dez. No grupo A, administrou-se uma dose única diária de octreotida (4 mig/kg/peso corporal/SC) enquanto no grupo B injetou-se por via SC solução salina a 0,9% em quantidade idêntica à utilizada para veicular octreotida. O grupo C serviu de controle. Os roedores foram inspecionados a respeito do volume diário do débito das fístulas, tempo necessário para sua cicatrização espontânea, avaliação clínico-bioquímica, hematológica e nutricional. Resultados: Os ratos tratados com octreotida não tiveram significantes alterações clínico-bioquímicas ou ponderais quando comparados ao controle (sem fístula) e cicatrizaram as fístulas espontaneamente em um tempo significativamente menor (3,8 ± 1,6 dias) que os do grupo B (15,3 ± 4,5 dias) (p < 0,05). No grupo B verificou-se queda ponderal média de 60% ao final da pesquisa, com 40% dos animais exibindo caquexia, anemia, hipoglobulinemia e hipoalbuminemia. Conclusão: A octreotida foi superior ao placebo e permitem afirmar que, segundo as estritas condições do experimento, o fármaco foi eficaz na cicatrização de fístulas enterocutâneas não complicadas de ratos.

Corticosteroids modulate the secretory processes of the rat intrahepatic biliary epithelium

We investigated the expression of glucocorticoid receptors (GcRs) in the intrahepatic biliary epithelium and the role of corticosteroids in the regulation of cholangiocyte secretion. GcR was studied by immunohistochemistry, reverse-transcription polymerase chain reaction, and Western blots. The effects of dexamethasone and budesonide on biliary bicarbonate excretion and H+/HCO3- transport processes were investigated in bile fistula rats, isolated intrahepatic bile duct units (IBDUs), and purified cholangiocytes. GcRs were expressed by rat cholangiocytes. Although acute administration of corticosteroids showed no effect, treatment for 2 days with dexamethasone or budesonide increased (P < 0.05) biliary bicarbonate concentration and secretion, which were blocked by the specific GcR antagonist, RU-486. IBDUs isolated from rats treated with dexamethasone or budesonide showed an increased (P < 0.05) activity of the Na+/H+ exchanger (NHE1 isoform) and Cl-/HCO3- exchanger (AE2 member), which was blocked by RU-486. Protein expression of NHE1 and AE2 and messenger RNA for NH1 but not AE2 were increased (P < 0.05) in isolated cholangiocytes by dexamethasone treatment. The intrahepatic biliary epithelium expresses GcR and responds to corticosteroids by increasing bicarbonate excretion in bile. This is caused by corticosteroid-induced enhanced activities and protein expression of transport processes driving bicarbonate excretion in the biliary epithelium.

Intestinal Absorption and Lymphatic Transport of a High γ-Linolenic Acid Canola Oil in Lymph Fistula Sprague-Dawley Rats

A new canola strain capable of producing >30% gamma-linolenic acid [GLA, 18:3(n-6)] in the seed oil has been developed in our laboratories. This study compares the intestinal absorption and lymphatic transport of this newly developed high GLA content canola oil (HGCO) with traditional GLA-rich borage oil (BO) using a lymph fistula rat model. To assess the extent that 1 mL of GLA in the supplemented oil was absorbed and transported, the fatty acid compositions of triglycerides in mesenteric lymph were compared over a 24-h collection period. The digestion, uptake and lymphatic transport of HGCO and the normal physiologic changes associated with fat absorption (e.g., lymph flow and an increase in lymphatic endogenous lipids outputs, triglycerides, cholesterol and phospholipids) were similar in the HGCO-and the BO-fed rats. The original differences in gamma-linolenic acid content in HGCO and BO were preserved in the fatty acid composition of the rats' lymph lipid. We conclude that the HGCO derived from the genetically modified canola plant is absorbed and transported into lymph similarly to BO.

Randomized Structured Triglycerides Increase Lymphatic Absorption of Tocopherol and Retinol Compared with the Equivalent Physical Mixture in a Rat Model of Fat Malabsorption

Previously we demonstrated that the digestion, absorption and lymphatic transport of lipid and key essential fatty acids (EFA) from randomly interesterified fish oil/medium-chain structured triglycerides (STG) were significantly higher than an equivalent physical mixture (PM) in a normal lymph fistula rat model and in a rat model of lipid malabsorption caused by ischemia/reperfusion (I/R) injury. The goals of this study were to further explore the potential absorptive benefits of STG by comparing the intestinal absorption and lymphatic transport of tocopherol and retinol when delivered gastrically with either STG or PM under normal conditions and after I/R injury to the small bowel. Food-deprived male Sprague-Dawley rats were randomly assigned to two treatments (sham controls or I/R). Under halothane anesthesia, the superior mesenteric artery (SMA) was occluded for 20 min and then reperfused in I/R rats. The SMA was isolated but not occluded in control rats. In both groups, the mesenteric lymph duct was cannulated and a gastric tube was inserted. Each treatment group received 1 mL of the fish oil/MCT STG or PM (7 rats/group) along with (14)C-alpha-tocopherol and (3)H-retinol through the gastric tube followed by an infusion of PBS at 3 mL/h for 8 h. Lymph was collected hourly for 8 h. Under steady-state conditions, the amount of (14)C-alpha-tocopherol and (3)H-retinol transported into lymph was significantly higher in the STG-fed rats compared with those fed PM in both control and I/R groups. In addition, control and I/R rats given STG had earlier steady-state outputs of (14)C-alpha-tocopherol and (3)H-retinol and maintained approximately 30% higher outputs in lymph throughout the 8-h lymph collection period compared with rats given the PM. We conclude that STG provides the opportunity to potentiate improved absorption of fat-soluble vitamins under normal and malabsorptive states.

Changes in collagenase and collagen gene expression after induction of aortocaval fistula in rats.

Progressive ventricular dilatation commonly accompanies the transition to overt failure in chronically overloaded hearts; however, only recently have studies begun to elucidate underlying molecular alterations. In particular, the potential role of altered myocardial expression of the procollagenase gene in this process has not previously been examined. Biventricular hypertrophy and dilatation were produced in rats by creating an abdominal aortocaval fistula. The time courses of changes in expression of collagen I and III genes and of the procollagenase gene (matrix metalloproteinase-1, MMP-1) were assessed by Northern blot hybridization. Expression of all three genes increased promptly; however, collagenase gene expression peaked much earlier (8 h) than did expression of either of the collagen genes (7 days), and all returned to baseline levels by 45 days. These data corroborate earlier reports of increased collagen gene expression in this model, but more importantly, they provide the first evidence of concurrent activation of collagenase gene expression, suggesting that enhancement of collagen degradation may be a prerequisite for structural cardiac dilatation.

Kupffer cell-derived cyclooxygenase-2 regulates hepatocyte Bcl-2 expression in choledocho-venous fistula rats

We have previously demonstrated that after bile duct ligation hepatocytes express Bcl-2, although the mechanisms regulating Bcl-2 expression were not identified. Our aim was to determine if biliary constituents induce hepatocellular expression of Bcl-2 by a cyclooxygenase-2 (COX-2)-dependent mechanism. We used the choledocho-venous fistula (CVF) rat model for these studies and inhibited COX-2 by feeding the animals nimesulide, a selective inhibitor of COX-2 activity. Serum bile acids were 70-fold greater in CVF animals compared with controls, although liver histology and serum alanine aminotransferase values remained normal for the duration of the study. Neither Bcl-2 nor COX-2 was detected in sham-operated animals. However, Bcl-2 was expressed in hepatocytes but not in other liver cells in the CVF animals. In contrast, COX-2 protein was identified in Kupffer cells but not in hepatocytes of CVF animals. Hepatic Bcl-2 protein expression was fourfold lower in the livers from nimesulide-treated CVF rats. In conclusion, high circulating concentrations of biliary constituents are associated with stimulation of de novo hepatocyte expression of Bcl-2 and Kupffer cell expression of COX-2. These data suggest Kupffer cell-derived prostanoids may regulate Bcl-2 expression in the hepatocyte.

Compensatory phospholipid digestion is required for cholesterol absorption in pancreatic phospholipase A2-deficient mice

Numerous studies have suggested phospholipid inhibition of dietary cholesterol absorption through the gastrointestinal tract. This study addressed the importance of luminal phospholipid hydrolysis in this process. The effect of phospholipase inhibition on cholesterol transport from intestinal lumen to the lymphatics was evaluated in lymph fistula rats. Cholesterol and phospholipid absorption efficiency in intact animals was evaluated in control and phospholipase A(2) (PLA2) gene-targeted mice. The PLA2 inhibitor FPL 67047XX retarded cholesterol absorption in a lymph fistula rat model. Under basal chow-fed dietary conditions, cholesterol absorption efficiency from a single bolus meal, and plasma lipid levels, were similar among PLA2+/+, PLA2+/-, and PLA2-/- mice. Interestingly, the nonhydrolyzable phospholipid dioleoyl ether phosphatidylcholine suppressed cholesterol absorption by 10% to 18% in mice without regard to their PLA2 genotype. When 1-palmitoyl-2-[(14)C]oleoyl-phosphatidylcholine was used as the substrate, the radiolabeled phospholipid was found to be hydrolyzed and absorbed with equal efficiency in PLA2+/+, PLA2+/-, and PLA2-/- mice. These results suggested that although phospholipid digestion in the intestinal lumen is a prerequisite for efficient cholesterol absorption, additional enzyme(s) can compensate for pancreatic PLA2 in catalyzing phospholipid digestion and facilitating cholesterol absorption in PLA2 knockout mice.

Ursodeoxycholic Acid Complexation with 2-Hydroxypropyl-β-Cyclodextrin Increases Ursodeoxycholic Acid Biliary Excretion after Single Oral Administration in Rats

Complexation of ursodeoxycholic acid (UDCA) with 2-hydroxypropyl-β-cyclodextrin (HPβCD) improves the water solubility and the dissolution rate of UDCA and may therefore increase its bioavailability. We compared the amount and the rate of biliary excretion of UDCA and biliary lipid secretion after a single oral administration of UDCA in 3 different pharmaceutical formulations [UDCA-HPβCD (‘urso-β-cyclodextrin’), UDCA suspension and UDCA capsule] at 3 different dosages each, in 11 groups (2 control groups) of bile fistula rats. UDCA excretion increased with an increase in dose, biliary UDCA recovery and peak secretion were significantly higher after administration of UDCA-HPβCD than after UDCA in suspension or capsule. This enhancement of biliary excretion may achieve greater UDCA enrichment in the bile acid pool than conventional pharmaceutical UDCA formulations, this giving to UDCA-HPβCD a considerable therapeutical potential.

The effect of etodolac on bile salt and histamine-mediated gastric mucosal injury in the rat

The effect of the selective cyclo-oxygenase-type-2 (COX-2) inhibitor etodolac on gastric mucosal integrity and gastric acid secretion was investigated in the rat. Etodolac was given in doses comparable with those being used in man for therapy of rheumatic conditions. The effect of etodolac was studied in the presence of a mild barrier breaker and in the presence of increased rates of endogenous acid secretion. In conscious pylorus-ligated rats, etodolac given intragastrically in 16 or 32 mg /kg for 3 h did not by itself give rise to visible gastric mucosal injury. Etodolac, however, exacerbated gastric mucosal injury evoked by intragastric application of acidified sodium taurocholate (5 mM in 150 mM HCl) in a dose-dependent manner. This effect of edotolac was independent of changes in gastric acid secretory responses. In rats whose gastric acid secretion was stimulated by intraperitoneal histamine (5 mg/kg), and etodolac (given i.g. in doses of 16 or 32 mg/kg) also increased gastric mucosal injury caused by histamine dose-dependently in the 3-h pylorus-ligated rats. Etodolac decreased gastric mucus in the saline- and in the sodium taurocholate-treated rats. In urethane-anaesthetized acute gastric fistula rats, intragastric etodolac (32 mg/kg) did not modify basal gastric acid secretion. Our data suggest that etodolac, a selective COX-2 inhibitor, impairs gastric mucosal resistance and can exacerbate gastric mucosal injury caused by other mucosal barrier breaking agents. Cyclooxygenase type-2 thus contributes to the gastric mucosal defences.

Dose-dependent conjugation of sulfobromophthalein and hepatic transit time in bile fistula rats: role of the microtubule-dependent vesicle pathway.

Sulfobromophthalein (BSP) is selectively taken up by the liver and secreted into the bile as unconjugated and conjugated forms. Our previous study demonstrated that unconjugated BSP, but not conjugated BSP, caused the dissociation of biliary lipid secretion from that of bile acids, suggesting that the hepatic BSP conjugation rate partly regulated biliary lipid secretion. To evaluate the mechanisms through which biliary lipid secretion is regulated by exogenous organic anions, we intravenously administered BSP to male Sprague-Dawley rats at various doses either continuously or as a bolus. Then the relationship of the dose of BSP to its conjugation rate, hepatic transit time, and biliary lipid secretion was determined. BSP decreased biliary secretion of cholesterol and phospholipids in a dose-dependent manner without affecting bile acid secretion. In contrast, the proportion of conjugated BSP in bile was associated with the dose. Although the serum clearance of BSP after bolus infusion was constant regardless of the dose administered (50 or 200 nmol/100 g), BSP secretion was delayed with increasing doses: unconjugated BSP was secreted predominantly in the early phase (0-15 min after bolus injection), and conjugated BSP was the predominant form in the late phase (15-30 min). Pretreatment with colchicine reduced the conjugation rate and hepatic transit time of BSP, suggesting that the microtubule-dependent vesicle pathway plays a role in biliary excretion and conjugation of BSP. We conclude that biliary lipid secretion is influenced by organic anions with an affinity for bile acids such as BSP and that this effect is dependent upon the hepatic metabolic rate, i.e., conjugation rate. The hepatic transit time also plays a key role in this process by influencing metabolism.

Enhancement of Jejunal Absorption of Conjugated Bile Acid by Neurotensin in Rats

Release of neurotensin (NT) from intestines is markedly stimulated by ingested fat, and NT may facilitate lipid digestion and absorption through various actions that are not fully understood. Our recent finding that NT stimulates hepatic output of bile acids only when bile delivery to the intestine is maintained has led us to investigate the effects of NT on bile acid absorption in the rat small intestine. We measured the effects of intravenous infusion of NT (3-10 pmol x kg(-1) x min(-1)) on biliary recovery of (3)H-taurocholate ((3)H-TC) and (3)H-cholate administered into proximal and distal intestines or into isolated intestinal segments in situ in biliary fistula rats. To further understand the underlying mechanisms involved, the effects of NT on intestinal absorption of (3)H-D-glucose, (3)H-leucine, (14)C-antipyrine, and (51)Cr-EDTA were investigated by monitoring the absorption of radioactivity into superior mesenteric venous blood. Infusion of NT, at doses that caused near physiologic increases in blood NT levels, increased biliary recovery of (3)H-TC from the jejunum (3.4-fold) and ileum (1.7-fold), but did not enhance absorption of (3)H-cholate. NT also facilitated transcellular uptake of (3)H-glucose and (3)H-leucine and increased paracellular uptake to (51)Cr-EDTA and (3)H-mannitol, but did not alter the absorption rate for (14)C-antipyrine. These results indicate that NT can exert a facilitative effect on intestinal bile acid absorption and return to liver. This effect of NT may involve increases in paracellular absorption and carrier-mediated transport by mechanisms not yet identified.

Volume overload cardiac hypertrophy exhibits decreased expression of g(s)alpha and not of g(i)alpha in heart.

We have recently reported enhanced levels of G(i)alpha proteins in genetic and other experimentally induced models of hypertension, whereas the levels of G(s)alpha were decreased in hypertensive rats expressing cardiac hypertrophy. The present studies were undertaken to investigate whether the decreased levels of G(s)alpha are associated with cardiac hypertrophy per se and used an aortocaval fistula (AV shunt; volume overload) rat model that exclusively expresses cardiac hypertrophy. Cardiac hypertrophy in Sprague-Dawley rats (200-250 g) was induced under anesthesia, and, after a period of 10 days, the hearts were used for adenylyl cyclase activity determination, protein quantification, and mRNA level determination. A temporal relationship between the expression of G(s)alpha proteins and cardiac hypertrophy was also examined on days 2, 3, 7, and 10 after induction of AV shunt in the rat. The heart-to-body-weight ratio (mg/g) was significantly increased in AV shunt rats after 3, 7, and 10 days of induction of AV shunt compared with sham-operated controls, whereas arterial blood pressure was not different between the two groups. Guanosine 5'-O-(3-thiotriphosphate) (GTPgammaS) stimulated adenylyl cyclase activity in a concentration-dependent manner in heart membranes from both groups; however, the degree of stimulation was significantly decreased in AV shunt rats. In addition, the stimulatory effects of isoproterenol were also diminished in AV shunt rats compared with control rats, whereas glucagon-stimulated adenylyl cyclase activity was not different in the two groups. The inhibitory effects of oxotremorine (receptor-dependent G(i) functions) and low concentrations of GTPgammaS on forskolin-stimulated adenylyl cyclase activity (receptor-independent G(i) functions) were not different in the two groups. In addition forskolin and NaF also stimulated adenylyl cyclase activity to a lesser degree in AV shunt rats compared with control rats. The levels of G(i)alpha-2 and G(i)alpha-3 proteins and mRNA, as determined by immunoblotting and Northern blotting, respectively, were not different in both groups; however, the levels of G(s)alpha(45) and G(s)alpha(47), and not of G(s)alpha(52), proteins were significantly decreased in AV shunt rats by days 7 and 10 compared with control rats, whereas no change was observed on days 2 and 3 after induction of AV shunt. These results suggest that the decreased expression of G(s)alpha proteins may not be the cause but the effect of hypertrophy and that the diminished responsiveness of adenylyl cyclase to GTPgammaS, isoproterenol, NaF, and forskolin in hearts from AV shunt rats may partly be due to the decreased expression of G(s)alpha. It can be concluded from these studies that the decreased expression of G(s)alpha may be associated with cardiac hypertrophy and not with arterial hypertension.