Restored TDCA and valine levels imitate the effects of bariatric surgery.

Background: Obesity is widespread and linked to various co-morbidities. Bariatric surgery has been identified as the only effective treatment, promoting sustained weight loss and the remission of co-morbidities. Methods: Metabolic profiling was performed on diet-induced obese (DIO) mice, lean mice, and DIO mice that underwent sleeve gastrectomies (SGx). In addition, mice were subjected to intraperitoneal (i.p.) injections with taurodeoxycholic acid (TDCA) and valine. Indirect calorimetry was performed to assess food intake and energy expenditure. Expression of appetite-regulating hormones was assessed through quantification of isolated RNA from dissected hypothalamus tissue. Subsequently, i.p. injections with a melanin-concentrating hormone (MCH) antagonist and intrathecal administration of MCH were performed and weight loss was monitored. Results: Mass spectrometric metabolomic profiling revealed significantly reduced systemic levels of TDCA and L-valine in DIO mice. TDCA and L-valine levels were restored after SGx in both human and mice to levels comparable with lean controls. Systemic treatment with TDCA and valine induced a profound weight loss analogous to effects observed after SGx. Utilizing indirect calorimetry, we confirmed reduced food intake as causal for TDCA/valine-mediated weight loss via a central inhibition of the MCH. Conclusions: In summary, we identified restored TDCA/valine levels as an underlying mechanism of SGx-derived effects on weight loss. Of translational relevance, TDCA and L-valine are presented as novel agents promoting weight loss while reversing obesity-associated metabolic disorders. Funding: This work has been supported in part by a grant from NIH (UO-1 A1 132898 to S.G.T., DP and MA). M.Q. was supported by the IFB Integrated Research and Treatment Centre Adiposity Diseases (Leipzig, Germany) and the German Research Foundation (QU 420/1-1). J.I. was supported by the Biomedical Education Program (BMEP) of the German Academic Exchange Service (DAAD). T.H. (HE 7457/1-1) and F.K. (KR 4362/1-1) were supported by the German Research Foundation (DFG). H.R.C.B. was supported the Swiss Society of Cardiac Surgery. Y.N. was supported by the Chinese Scholarship Council (201606370196) and Central South University. H.U., T.M. and R.M. were supported by the Osaka Medical Foundation. C.S.F. was supported by the German Research Foundation (DFG, SFB738, B3).

Nonclinical toxicology studies with sodium taurodeoxycholate: acute and subacute toxicity in dogs.

Sodium taurodeoxycholate (TDCA) has been investigated for various inflammatory disorders such as sepsis. We recently evaluated nonclinical safety profile of TDCA using rats infused intravenously. As a series of preclinical safety investigations, we further conducted toxicity studies with TDCA delivered to dogs via intravenous administration under Good Laboratory Practice regulation in this study. In dose range-finding study (dose escalation study), dogs given with TDCA at a dose of 150 mg/kg showed marked changes in clinical signs, hematology, and serum biochemistry. And biochemical markers of liver damage and local skin lesions were observed following intravenous infusion of 100 mg/kg TDCA, suggesting that 100 mg/kg was chosen as the highest dose of TDCA for 4-week repeated-dose toxicity study using dogs. Despite no treatment-related significant changes in body weight, food consumption, ophthalmoscopy, and urinalysis, skin lesions were observed at the injection site of animals administered with higher than 50 mg/kg of TDCA along with biochemical and histopathological changes associated with liver injury. However, most of off-target effects were found to be reversible since these were recovered after stopping TDCA infusion. These findings indicate that the no-observed-adverse-effect-level (NOAEL) for TDCA in dogs was considered to be 5 mg/kg/d. Taken together, our results provide important toxicological profiles regarding the safe dose of TDCA for drug development or clinical application.

Evaluation of acute and subacute toxicity of sodium taurodeoxycholate in rats.

Taurodeoxycholate (TDCA) inhibits various inflammatory responses suggesting potential clinical application. However, the toxicity of TDCA has not been evaluated in detail in vivo. We investigated the acute toxicity and 4-week repeated-dose toxicity of TDCA following intravenous infusion under Good Laboratory Practice regulations. In the sighting study of acute toxicity, one of two rats (one male and one female) treated with 300 mg/kg TDCA died with hepatotoxicity, suggesting that the approximate 50% lethal dose of TDCA is 300 mg/kg. Edema and discoloration were observed at the injection sites of tails when rats were infused with 150 mg/kg or higher amount of TDCA once. In 4-week repeated-dose toxicity study, no treatment-related mortality or systemic changes in hematology and serum biochemistry, organ weights, gross pathology, or histopathology were observed. However, the tail injection site showed redness, discharge, hardening, and crust formation along with histopathological changes such as ulceration, edema, fibrosis, and thrombosis when rats were infused with 20 mg/kg TDCA. Taken together, TDCA induced no systemic toxicity or macroscopic lesions at the injection site at a dose of 10 mg/kg/day, which is 33 times higher than the median effective dose observed in a mouse sepsis model. These findings suggest that TDCA might have a favorable therapeutic index in clinical applications.

In vitro and in vivo preclinical evaluation of a minisphere emulsion-based formulation (SmPill®) of salmon calcitonin.

Salmon calcitonin (sCT, MW 3432Da) is a benchmark molecule for an oral peptide delivery system because it is degraded and has low intestinal epithelial permeability. Four dry emulsion minisphere prototypes (SmPill®) containing sCT were co-formulated with permeation enhancers (PEs): sodium taurodeoxycholate (NaTDC), sodium caprate (C10) or coco-glucoside (CG), or with a pH acidifier, citric acid (CA). Minispheres protected sCT from thermal degradation and the released sCT retained high bioactivity, as determined by cyclic AMP generation in T47D cells. Pre-minisphere emulsions of PEs combined with sCT increased absolute bioavailability (F) compared to native sCT following rat intra-jejunal (i.j.) and intra-colonic (i.c.) loop instillations, an effect that was more pronounced in colon. Minispheres corresponding to ~2000I.U. (~390µg) sCT/kg were instilled by i.j. or i.c. instillations and hypocalcaemia resulted from all prototypes. The absolute F (i.j.) of sCT was 11.0, 4.8, and 1.4% for minispheres containing NaTDC (10µmol/kg), CG (12µmol/kg) or CA (32µmol/kg) respectively. For i.c. instillations, the largest absolute F (22% in each case) was achieved for minispheres containing either C10 (284µmol/kg) or CG (12µmol/kg), whilst the absolute F was 8.2% for minispheres loaded with CA (32µmol/kg). In terms of relative F, the best data were obtained for minispheres containing NaTDC (i.j.), a 4-fold increase over sCT solution, and also for either C10 or CG (i.c.), where there was a 3-fold increase over sCT solution. Histology of instilled intestinal loops indicated that neither the minispheres nor components thereof caused major perturbation. In conclusion, selected SmPill® minisphere formulations may have the potential to be used as oral peptide delivery systems when delivered to jejunum or colon.

Supplementation of tauroursodeoxycholic acid during IVC did not enhance in vitro development and quality of buffalo IVF embryos but combated endoplasmic reticulum stress.

Endoplasmic reticulum (ER) stress, a dysfunction in protein-folding capacity of ER, is involved in many pathologic and physiological responses including embryonic development. This study investigated the effect of supplementation of IVC medium with an ER stress inducer, tunicamycin (TM), and an inhibitor, tauroursodeoxycholic acid (TUDCA), on the developmental competence, apoptosis, and gene expression in buffalo embryos produced by IVF. Treatment of presumed zygotes with TM resulted in a significant (P < 0.01) decrease in the blastocyst rate, whereas TUDCA supplementation did not improve the blastocyst development rate. Further, presence of TUDCA could not ameliorate the adverse effects of TM in terms of the blastocyst rate in combined (TM + TUDCA) treatment. Tunicamycin treatment increased (P < 0.01) the apoptotic index and reduced the total cell number, whereas TUDCA did not affect them significantly. However, TUDCA reduced the extent of TM-mediated apoptosis during combined (TM + TUDCA) treatment. Tunicamycin treatment increased (P < 0.01) and TUDCA treatment decreased (P < 0.01) the expression level of ER chaperones, GRP78 and GRP94. In the combined TM + TUDCA treatment, TUDCA decreased their expression level compared to that in the controls. A similar pattern was observed in the case of proapoptotic gene BAX. We did not find any significant difference in the expression level of BCl-XL, BID, P53, and CASPASE 3 after TM and TUDCA supplementation. In conclusion, our study reported that TM induces ER stress in buffalo embryos produced in vitro resulting in a decrease in the blastocyst rate and an increase in the level of apoptosis and that these actions are mediated by modulating the expression of apoptosis-related genes and ER chaperones. Tauroursodeoxycholic acid did not improve the developmental potential of buffalo embryos; however, it attenuated the TM-induced apoptosis by downregulating BAX and ER chaperones.

Dietary bile acid supplementation improves intestinal integrity and survival in a murine model.

PURPOSE: In vitro supplementation of the bile salt, taurodeoxycholic acid (TDCA), has been shown to stimulate proliferation and prevent intestinal apoptosis in IEC-6 cells. We hypothesize that addition of TDCA to a rodent liquid diet will be protective against induced intestinal injury. METHODS: C57Bl6 mice were fed a liquid diet with or without 50-mg/(kg d) TDCA supplementation. After 6 days, the mice were injected with lipopolysaccharide (LPS) (10 mg/kg) to induce intestinal injury. Specimens were obtained 24 hours later and evaluated for intestinal apoptosis, crypt proliferation, and villus length. A separate cohort of animals was injected with LPS (25 mg/kg) and followed 7 days for survival. RESULTS: Mice whose diet was supplemented with TDCA had significantly increased survival. After LPS-induced injury, mice supplemented with TDCA showed decreased intestinal apoptosis by both H&E and caspase-3. They also had increased intestinal proliferation by 5-bromo-2'deoxyuridine staining and increased villus length. CONCLUSIONS: Dietary TDCA supplementation alleviates mucosal damage and improves survival after LPS-induced intestinal injury. Taurodeoxycholic acid is protective of the intestinal mucosa by increasing resistance to injury-induced apoptosis, stimulating enterocyte proliferation, and increasing villus length. Taurodeoxycholic acid supplementation also results in an increased survival benefit. Therefore, bile acid supplementation may potentially protect the intestine from injury or infection.

Enhanced intestinal absorption of salmon calcitonin (sCT) from proliposomes containing bile salts.

PURPOSE: The feasibility of using proliposomes containing salmon calcitonin (sCT) and absorption enhancing agents, as an oral delivery system, to improve the intestinal absorption of sCT was explored using rats and Caco-2 cell systems. METHODS: Seventeen surfactants were examined for their effects with reference to accelerating the permeability of sCT (300 microg/ml) across Caco-2 cell monolayers, and damage to the intestinal epithelial cells, as measured by the change in transepithelial electrical resistance (TEER) across the cell monolayer. Proliposomes containing sCT (0.75%, w/w) and sodium taurodeoxycholate (NaTDC, 2.5%, w/w) (TDC proliposomes) were prepared according to the standard method using sorbitol and phosphatidylcholine as core and wall-forming materials, respectively, administered intra-duodenally to rats, and plasma concentrations of sCT were subsequently determined by LC-MS. RESULTS: Among the surfactants examined, some bile salts including NaTDC appeared to be the most advantageous when estimated based on the balance between the permeation enhancement (e.g., a 10.8-fold increase in the permeability of sCT for 0.1% NaTDC) and damage to the cells (e.g., a 3.55-fold decrease in the TEER value for 0.1% NaTDC). The administration of TDC proliposomes resulted in a 7.1-fold increase in the bioavailability (i.e., 0.49%) of sCT, when administered duodenally to rats. The size of the reconstituted liposomes in water was significantly smaller (e.g., 23.2 nm, number weighted diameter), and the entrapment efficiency (EE) of sCT in the reconstituted liposomes was 2.8-fold larger (54.9%), for TDC proliposomes, compared to proliposomes prepared without NaTDC (sCT proliposomes). CONCLUSION: A 7.1-fold increase in the bioavailability of sCT could be achieved from the TDC proliposomes. In addition to the intrinsic activity of the bile salt to fluidize the membrane, the simultaneous delivery of sCT and NaTDC to the site of absorption in the intestine via proliposomes and the subsequent formation of lipophilic ion-pair complexes between sCT and NaTDC at the site might have been contributing factors in this outstanding absorption enhancement.

Unique inhibition of bile salt-induced apoptosis by lecithins and cytoprotective bile salts in immortalized mouse cholangiocytes.

Bile duct epithelium is physiologically exposed to high concentrations of bile salts, suggesting the presence of a cytoprotective mechanism(s). The aim of this study was to clarify whether bile salts cause bile duct cell damage and to elucidate the mechanism(s) providing protection against such an action of bile salts. Immortalized mouse cholangiocytes were incubated with taurocholate, taurochenodeoxycholate, glycochenodeoxycholate (GCDC), taurodeoxycholate, and tauroursodeoxycholate (TUDC), followed by flow-cytometric analysis and caspase activity assay to evaluate the induction of apoptosis. GCDC time-dependently induced caspase 3 (3.4-fold)- and caspase 9 (1.4-fold)-mediated apoptosis of cholangiocytes, but this was inhibited by lecithins and TUDC. Further, expression of cholangiocyte bile salt transporters (apical sodium-dependent bile salt transporter [Asbt] and multidrug resistance protein 3 [Mrp3]) was examined by RT-PCR and western blotting, and cholangiocyte bile salt uptake was determined using radiolabeled bile salts. Expression of cholangiocyte Asbt and Mrp3 was increased by bile salts, whereas lecithins interestingly reduced bile salt uptake to inhibit cholangiocyte apoptosis. In conclusion, bile salts themselves cause cholangiocyte apoptosis when absorbed by and retained inside the cell, but this is inhibited by washing out cytotoxic bile salts according to Mrp3, a rescue exporting molecule. Biliary lecithin is seemingly another cytoprotective player against cytotoxic bile salts, reducing their uptake, and this is associated with a reduced expression of Mrp3.

Effect of chronic administration of tauro-hyodeoxycholic acid on biliary bile acid composition and on biliary lipid secretion in humans.

BACKGROUND: Tauro-hyodeoxycholic acid is a hydrophilic bile acid of potential interest for treating cholestatic liver diseases. Bile acid pool is enriched with this bile acid during acute administration in patients with interrupted enterohepatic circulation. The aim of our study was to check the effect of chronic administration of tauro-hyodeoxycholic acid on biliary lipid composition and secretion in man with intact enterohepatic circulation. METHODS: We studied 7 dyspeptic patients before and during taurohyodeoxycholic acid 750 mg/day given for 6-8 weeks. We measured bile acid composition in duodenal aspirate, and biliary lipid secretion was also measured in 5 of these patients using a duodenal perfusion technique. RESULT: Tauro-hyodeoxycholic was undetectable in duodenal aspirate in all patients before treatment, and was 2%, 4%, 5%, 7%, 7%, 8% and 13% of biliary bile acid during treatment in individual patients. The proportion of cholic, deoxycholic, chenodeoxycholic ursodeoxycholic and lithocholic acid was similar before and during treatment. Bile acid duodenal output remained unchanged during taurohyodeoxycholic by comparison with pretreatment with median difference -0.3 mmol (95% confidence interval 1.6 mmol). The corresponding difference for duodenal cholesterol and phospholipid output was 0.1 mmol (0.2 mmol) and 0.2 mmol (0.6 mmol). CONCLUSIONS: By contrast with acute administration in patients with interrupted enterohepatic circulation, chronic administration of tauro-hyodeoxycholic to man with intact enterohepatic circulation has little effect on biliary lipid composition and secretion.

Acute effects of bile acids on the pancreatic duct epithelium in vitro.

BACKGROUND: Acute pancreatitis is associated with passage of gallstones, although the mechanism(s) linking the two processes remains undefined. Bile reflux into the pancreatic duct could play a role but the experimental conditions often employed to induce pancreatitis rarely develop clinically. Here we examined whether low concentrations of bile affect ductal electrophysiology as an indirect measure of ductal epithelial integrity and function in vitro. METHODS: The main duct was dissected out of freshly harvested bovine pancreata, cut into 1- x 2-cm sections, placed in tissue culture for 48-72 h, then placed in Ussing chambers. Changes in tissue resistance (Rt) and short-circuit current (Isc) were monitored. The responses to forskolin and bile (taurodeoxycholic acid, TDCA) were examined separately and together. RESULTS: Forskolin (10 microM) produced a decrease in the Isc without a significant change in Rt, suggesting a secretory response, followed by a return to baseline. TDCA caused a similarly reversible decrease in the Isc at low doses, but a persistent drop at higher concentrations. A concurrent drop in Rt was noted at all TDCA concentrations, the duration of which correlated with dosage and degree of histological damage. Prior exposure to low (0.5 mM) doses of TDCA significantly blunted the response to subsequent forskolin challenge. CONCLUSIONS: Acute exposure to TDCA in vitro causes epithelial damage at levels lower than those normally used to induce experimental pancreatitis. At the lower concentrations, Rt returns to baseline rapidly, suggesting recovery (restitution) from epithelial damage but with a persistent loss of the response to forskolin. Reflux of minute amounts of bile into the pancreatic duct could play a significant role in the pathogenesis of gallstone pancreatitis by uncoupling the normal stimulus-secretion apparatus of the ductal system and breaking down the epithelial barrier.

Taurohyodeoxycholic acid protects against taurochenodeoxycholic acid-induced cholestasis in the rat.

The prevention of the hepatotoxic effects produced by intravenous infusion of taurochenodeoxycholic acid (TCDCA) by coinfusion with taurohyodeoxycholic acid (THDCA) was evaluated in bile fistula rats; the hepatoprotective effects of the latter were also compared with those of tauroursodeoxycholic acid (TUDCA). Rats infused with TCDCA at a dose of 8 micromol/min/kg showed reduced bile flow and calcium secretion, as well as increased biliary release of alkaline phosphatase (AP) and lactate dehydrogenase (LDH). This was associated with a very low biliary secretion rate of TCDCA (approximately 1 micromol/min/kg). Simultaneous infusion of THDCA or TUDCA at the same dose preserved bile flow and almost totally abolished the pathological leakage of the two enzymes into bile. The effect was slightly more potent for THDCA. The maximum secretion rate of TCDCA increased to the highest value (8 micromol/min/kg) when coinfused with either of the two hepatoprotective bile acids (BA), which were efficiently and completely secreted in the bile, without metabolism. Calcium output was also restored and phospholipid (PL) secretion increased with respect to the control saline infusion. This increase was higher in the THDCA study. These data show that THDCA is highly effective in the prevention of hepatotoxicity induced by intravenous infusion of TCDCA by facilitating its biliary secretion and reducing its hepatic residence time; this was associated with selective stimulation of PL biliary secretion.

Mediators of exocrine pancreatic secretion induced by intraduodenal application of bile and taurodeoxycholate in man.

The aim of the study was to investigate whether cholecystokinin, neurotensin, and cholinergic mechanisms act as mediators of bile salt-stimulated exocrine pancreatic secretion. Ten fasting healthy subjects provided with a double-lumen tube received 2, 4, and 6 g cattle bile and 200, 400, and 600 mg Na-taurodeoxycholate (TDC) into the duodenum at 65-min intervals, respectively. The application of TDC was repeated in another 10 subjects after intravenous bolus injection of 2.5 micrograms/kg b.w. atropine followed by continuous infusion of 5 micrograms/kg.h. Secretions of volume, bicarbonate, trypsin, and lipase were determined in 10-min fractions of duodenal juice. Plasma samples were analysed for cholecystokinin-like immunoreactivity (CCK-LI) and neurotensin with radioimmunoassays. Volume, bicarbonate, trypsin, and lipase secretion rates were significantly increased by 4 g and 6 g bile and by all doses of TDC. Incremental volume and bicarbonate output was dose-dependently enhanced by bile and TDC, and trypsin and lipase output by bile. Atropine significantly decreased the baseline values and all responses to TDC. Plasma concentrations and integrated CCK-LI and neurotensin significantly increased after 4 and 6 g bile and after 400 and 600 mg TDC. Atropine did not significantly influence peptide release. It is concluded that both hydrokinetic and ecbolic pancreatic secretion stimulated by intraduodenal bile and TDC are dependent on a cholinergic tone. CCK and probably also neurotensin act as further mediators of the ecbolic effect.

Exocrine pancreatic secretion and plasma levels of cholecystokinin, pancreatic polypeptide, and somatostatin after single and combined intraduodenal application of different bile salts in man.

Bile salts are intraduodenal stimulants of basal pancreatic secretion. This study aims to show whether the three main bile salts of human bile differ in their action on pancreatic secretion, and whether they enhance or inhibit each other after combined use. Furthermore, the effect on gastroenteropancreatic peptide release is evaluated. Twelve subjects were provided with a gastroduodenal double-lumen tube. Equimolar doses (0.6 mmol) of taurocholate (322 mg), taurodeoxycholate (313 mg), and a combination of both stimuli were given intraduodenally. Another 12 subjects received taurochenodeoxycholate (313 mg) instead of taurocholate. Volume, bicarbonate, trypsin, and lipase were determined in duodenal aspirates. Cholecystokinin, pancreatic polypeptide, and somatostatin were measured radioimmunologically in plasma samples. All bile salts and combinations exerted a significant hydrokinetic and ecbolic effect. The hydrokinetic response of the combined stimuli was significantly higher as compared with taurocholate and taurochenodeoxycholate, respectively. As far as concerns the ecbolic response, the difference was significant only for trypsin output as compared with taurochenodeoxycholate. Plasma cholecystokinin rose significantly only after the combined stimuli. Pancreatic polypeptide and somatostatin increased significantly after all stimuli, except pancreatic polypeptide after taurocholate. Combined use enhances the hydrokinetic and ecbolic effects of single bile salts. Cholecystokinin may, hereby, be involved as a mediator of the ecbolic effect. Pancreatic polypeptide release indicates cholinergic mechanisms as further mediators. As demonstrated by somatostatin release, counter-regulatory mechanisms are also triggered by intraduodenal bile salts.

Effect of intraduodenal taurodeoxycholate and L-phenylalanine on pancreatic secretion and on gastroenteropancreatic peptide release in man.

Intraduodenally applied bile salts and essential amino acids are known to stimulate exocrine pancreatic secretion. There are contradictory reports, however, about an interaction of both stimuli with respect to pancreatic function. The intention of the study was to compare the effects of equimolar amounts of taurodeoxycholate and L-phenylalanine used singularly and combined on pancreatic secretion and on gastroenteropancreatic peptide release. In 12 healthy subjects, 0.8 mmol of Na-taurodeoxycholate (410 mg) and L-phenylalanine (130 mg) were separately and combined applied into the duodenum in a randomized order. Volume, bicarbonate, trypsin, lipase, and amylase secretion as well as cholecystokinin, pancreatic polypeptide, and somatostatin plasma levels were measured. Volume and bicarbonate secretion was significantly enhanced by taurodeoxycholate. The effect was stronger compared to L-phenylalanine. The increase of enzyme secretion was comparable. After combined application, the ecbolic effect was insignificantly smaller, whereas the hydrokinetic effect was between those of the single stimuli. Plasma levels of cholecystokinin, pancreatic polypeptide, and somatostatin rose concomitantly with the pancreatic response. On an equimolar basis taurodeoxycholate results in a stronger hydrokinetic effect than L-phenylalanine. Their ecbolic effects, however, are comparable. In addition to cholinergic mechanisms, as indicated by the PP release observed, cholecystokinin may also act as a mediator. In combined application, the stimuli interfere with each other. Somatostatin and pancreatic polypeptide are not responsible for this mutual inhibition.

Bile salt hydrophobicity influences cholesterol recruitment from rat liver in vivo when cholesterol synthesis and lipoprotein uptake are constant.

These studies were undertaken to characterize the role of bile salt hydrophobicity in determining the rate of cholesterol recruitment from the liver. Using an in vivo rat model in which the acquisition of hepatic cholesterol from chylomicron remnants, low-density lipoproteins, and de novo synthesis was measured and kept constant, it was found that the amount of sterol recruited from the liver cell increased progressively as the liver was probed with a constant infusion of progressively more hydrophobic bile salts. The absolute secretion rate of both cholesterol and phospholipid increased nearly 50% as the hydrophobic index of the bile salts traversing the liver increased from 1.7 to 4.5, but the ratio of cholesterol to phospholipid secreted in bile remained nearly constant. Thus, when cholesterol entry into the hepatocyte via lipoproteins and de novo cholesterol synthesis is constant, the mass of cellular cholesterol recruited into the bile is directly proportional to the hydrophobic-hydrophilic balance of the secreted bile salts.

Evaluation of in vivo measurement of transesophageal electrical resistance as an indicator of early experimental esophageal mucosal injury.

Experimental esophageal mucosal injury has been characterized by an increase in mucosal permeability to acid and a fall in transmucosal electrical potential difference (PD). We have developed a technique for measuring transesophageal electrical resistance in an in vivo rabbit model of esophageal injury and have performed experiments to assess this parameter as an index of esophageal injury. As expected, tissue resistance varied inversely with mucosal area. The current-voltage plot for the esophagus with or without trypsin, bile, or acid injury remained linear with no "breakpoints." Tissue resistance was compared with standard indices of mucosal injury such as acid flux, PD, and morphologic change in experimental esophageal injury due to acid, bile, and trypsin. Our results show that tissue resistance is more sensitive than either PD or acid flux in detecting early esophageal injury due to low concentrations of acid or trypsin and, as opposed to PD, always showed a persistent, unidirectional change with injury. Thus these data show that in vivo measurement of transesophageal electrical resistance is a useful technique for assessing esophageal mucosal injury, in that it is the most sensitive indicator of esophageal injury we have observed.

Bile acid structure and biliary lipid secretion. II. A comparison of three hydroxy and two keto bile acids.

The effect of five bile acids on biliary lipid secretion was studied in the pentobarbital-anesthetized cat. The dihydroxy acid, taurohyodeoxycholic acid, was indistinguishable from another dihydroxy acid, taurochenodeoxycholic acid, but secretion of both phospholipid and cholesterol was considerably reduced with two mono-keto dihydroxy acids, tauro-3alpha,12alpha-dihydroxy-7-keto-5beta-cholanoic acid and tauro-3alpha,7alpha-dihydroxy-12-keto-5beta-cholanoic acid. The effect of a trihydroxy bile acid, taurocholic acid was as previously described. The effect of the keto bile acids may be explained by the ability of these bile acids to solubilize lipid, but such an explanation is inadequate for the difference between di- and trihydroxy bile acids. An intracellular effect of bile acid is postulated.