Diclofenac and dexamethasone modulate the effect of cannabidiol on the rat colon motility ex vivo

Introduction

Due to the growing interest in the use of cannabinoids in supportive therapies, they are increasingly used together with anti-inflammatory drugs. Cannabinoids inhibit gastrointestinal motility, while steroidal and nonsteroidal anti-inflammatory drugs influence motility in other ways. The aim of the research was to study the interactions between cannabidiol (CBD) and these two classes of anti-inflammatory drugs in the context of gastrointestinal motility. Dexamethasone (DEX) was selected as a steroidal drug and diclofenac (DCF) as a nonsteroidal counterpart.

Material and Methods

The experiments were performed on isolated rat colon strips in isometric conditions. The contractile response to acetylcholine (ACh) (1 μM) was measured with no substance applied as a control value and was measured after application of CBD (80 μM), DEX (100 μM), DCF (100 μM), or a combination of these substances.

Results

Cannabidiol strongly inhibited intestinal motility mediated by ACh application, DCF inhibited it non-significantly, while DEX intensified it. When CBD was co-administered with DEX, the combination inhibited intestinal motility non-significantly relative to the ACh-only control. Co-administration of CBD with DCF inhibited motility more than when these substances were administered separately.

Conclusion

Inhibition of the intestinal response to ACh is likely due to the synergistic effect of CBD and endogenous cannabinoids. Dexamethasone lessened the inhibitory effect of CBD, likely because of diminished availability of the arachidonic acid necessary for endogenous cannabinoid synthesis. However, diclofenac may increase endogenous cannabinoid synthesis, because of the greater availability of arachidonic acid caused by DCF blocking the cyclooxygenation pathway.

Phytogenic Compounds for Enhancing Intestinal Barrier Function in Poultry-A Review

After the European Union ban of antibiotic growth promoters, works on different methods of improving gut health have intensified. The poultry industry is struggling with problems that were previously controlled by antibiotic growth promoters, therefore the search for optimal solutions continues. Simultaneously, there is also increasing social pressure to minimize the use of antibiotics and replace them with alternative feed additives. A variety of available alternatives is considered safe by consumers, among which phytogenics play a significant role. However, there are still some limitations that need to be considered. The most questionable are the issues related to bioavailability, metabolism of plant derivatives in birds, and the difficulty of standardizing commercial products. There is still a need for more evidence-based recommendations for the use of phytogenics in livestock. On the other hand, a positive influence of phytogenic compounds on the health of poultry has been previously described by many researchers and practical application of these compounds has auspicious perspectives in poultry production. Supplementation with phytogenic feed additives has been shown to protect birds from various environmental threats leading to impaired intestinal barrier function. Phytogenic feed additives have the potential to improve the overall structure of intestinal mucosa as well as gut barrier function on a molecular level. Recognition of the phytogenics' effect on the components of the intestinal barrier may enable the selection of the most suitable ones to alleviate negative effects of different agents. This review aims to summarize current knowledge of the influence of various phytogenic constituents on the intestinal barrier and health of poultry.

Evaluation of the effects of Bidens tripartita extracts and their main constituents on intestinal motility - An ex vivo study

ETHNOPHARMACOLOGICAL RELEVANCE

Based on traditional medicine, infusions of Bidens species (Asteraceae) have been successfully used in the treatment of acute and chronic enteritis. Additionally, ethnopharmacological reports demonstrating the gastrointestinal, gastroprotective, anti-inflammatory, antiulcerogenic and immunomodulatory potency of Bidens tripartita Linn. (Asteraceae) and its constituents make the plant a particularly interesting herbal drug candidate for the supportive treatment of functional gastrointestinal and motility disorders.

AIM OF THE STUDY

The study aimed to verify the effects of B. tripartita and its main flavonoid constituents on intestinal contractility patterns under ex vivo conditions.

MATERIALS AND METHODS

The effects of B. tripartita preparations and their main flavonoids were identified using an alternative model of porcine isolated jejunum specimens. Using LC-ESI-MS, the effects of six different standardized extracts, aqueous (BT1), methanolic 50% (BT2), methanolic (BT3), diethyl ether (BT4), ethyl acetate (BT5) and butanol (BT6) (0.001-0.1 mg/mL), as well as three pure isolated flavonoids, luteolin (LUT), cynaroside (CYN) and flavanomarein (ION) (0.001-100 μM), were evaluated towards spontaneous and acetylcholine-induced motility.

RESULTS AND CONCLUSION

s: The results showed the potent prokinetic effects of the B. tripartita extracts and their flavonoids on jejunum smooth muscle. The myocontractile effect was observed on both spontaneous and acetylcholine-induced contractility. There were no substantial differences in the magnitude of myocontractile effects between all six extracts with the exception of the butanol extract which seemed to have a slightly stronger prokinetic effect than the other extracts. The use of extracts at the highest tested concentrations provoked an approximately 1.5-fold increased reaction to acetylcholine compared to the control treatment. The myocontractile effect of the single flavonoids justifies the hypothesis that these secondary metabolites are responsible for the prokinetic activity of all the tested extracts. Among the tested flavonoids, CYN appeared to be the most potent ingredient of B. tripartita; the increase in the response to acetylcholine in the presence of this compound exceeded 250% of the control reaction. In view of the obtained results, the range of functional gastrointestinal disorders in which B. tripartita could be expected to bring benefits include the predominantly constipative phases of irritable bowel syndrome and dyspeptic complaints in which treatment protocols usually involve gastroprokinetics.

The impact of chlorophyllin on deoxynivalenol transport across jejunum mucosa explants obtained from adult pigs

Regardless of the efforts put into preventing or reducing fungal growth, extensive mycotoxin contamination has been reported in animal feeds. In the case of pigs, one of the mycotoxins of major concern is deoxynivalenol (DON). The use of adsorbents as feed additives represents one of the strategies to control mycotoxins' contamination in feedstuff. Therefore, the aim of the study was to verify the ability of chlorophyllin (CHL) to reduce the absorption rate of DON in swine mucosa explants. Intestine was obtained from routinely slaughtered adult pigs. The mucosa explants were studied by means of Ussing chamber technique. The effect of DON (10 and 30 μg/ml) on mucosa viability and permeability and CHL (100 μg/ml) impact on DON (30 μg/ml) absorption was verified. The results revealed that mucosa explants isolated from adult animals remained unaffected for 90 min in the presence of DON in the lower concentration (10 μg/ml). Mycotoxin in the higher dose (30 μg/ml) increased mucosa permeability (decreased transepithelial electrical resistance value) and enhanced paracellular transport of lucifer yellow and mannitol but did not affect lactate dehydrogenase leakage. The introduction of CHL neither diminished the absorption rate of DON across swine mucosa explants nor prevented the toxic effects of DON on intestine. In conclusion, the results confirm the negative effect of DON on pig jejunum mucosa. However, the toxic effect of DON was observed only when it was used in relatively high doses. A promising adsorbent agent, CHL, failed to reduce the intensity of DON transport across intestine under in vitro conditions.

Modulations of bovine hepatic microsomal metabolism of benzimidazoles by secondary plant metabolites

The study was aimed to estimate the effect of plant secondary metabolites present in ruminants diet and phytogenic feed additives on liver microsomal metabolism of albendazole and fenbendazole. The selected phytocompounds comprised of flavonoids (apigenin, quercetin) and saponins (hederagenin, medicagenic acid). The experiments were performed on liver microsomal fraction obtained from routinely slaughtered cows. The intensity of albendazole and fenbendazole metabolism in the presence of flavonoids and saponins was analyzed in equimolar concentration (100 μM). The obtained results revealed that both flavonoids and saponins intensify the metabolism of albendazole and fenbendazole in bovine microsomes. In the case of albendazole, apigenin and quercetin doubled the amount of degraded drug and the amount of produced albendazole sulfoxide. Additionally, both flavonoids increased the amount of produced albendazole sulfone. Saponins, hederagenin, and medicagenic acid intensified the degradation of albendazole (1.8-fold) and the production of albendazole sulfoxide (twofold). Medicagenic acid inhibited the production of albendazole sulfone. In the case of fenbendazole, the degradation of the drug and the production of oxfendazole were increased four and five times in the presence of saponins and flavonoids, respectively. The enhancement of benzimidazoles' metabolism caused by the studied plant metabolites could change pharmacokinetics and the efficacy of benzimidazoles' treatment in cattle.

The effect of pyriproxyfen on the motoric activity of rat intestine - In vitro study

The application of pyriproxyfen (PPF) to drinking water and constant exposure of the whole population to this insecticide is an unprecedented action on a world scale and presents a new and serious challenge for toxicology. The aim of the study was to evaluate the potential effect of PPF on the intestine muscle activity. The experiments were performed on isolated duodenum and jejunum strips of rat, in isometric conditions. Doses of PPF in the range of 0.032-100 μM were used in the experiments. The obtained results indicate that PPF affected significantly the spontaneous activity of duodenum and jejunum strips, PPF caused the muscle relaxation when used in the concentration of 0.8 μM and higher. The reaction to acetylcholine (ACh) when PPF preceded or followed ACh application was also reduced. It is demonstrated that the reduction of the contraction caused by ACh was stronger when duodenum strips were preincubated in the presence of PPF solution than in case of ACh-precontracted strips. The first significant reaction of duodenal strips appeared in the presence of PPF in a dose of 0.16 μM and 0.8 μM when the insecticide application preceded and followed ACh treatment, respectively. Besides, the duodenum turned out to be much more susceptible to the tested insecticide than jejunum. Taking into account PPF kinetic data obtained in animals, the observed disturbances were caused by the insecticide used in relatively high concentrations. However, the full risk estimation requires the kinetic data obtained in human, especially from monitoring studies on general population after long-term exposure to PPF.

A Simple Method for Hepatocyte Attachment in Hollow Fibre Bioreactors

A new method for hepatocyte attachment in hollow fibre (HF) bioreactors was proposed and verified. A flow of medium with suspended hepatocytes, evoked by transmembrane pressure (TMP), and directed across the membrane into the fibre lumen, has accelerated and improved hepatocyte contact with the HF. It was found that seeding of hepatocytes onto the membrane was optimal at TMP of 50–80 mmHg. Ammonia utilisation and ureagenesis rates in hepatocytes seeded in the bioreactor suggests that the proposed method warrants proper conditions for cell functionality and allows for extended culture of hepatocytes in HF bioreactors. It is speculated that time cutback between introduction of hepatocytes into the bioreactor and the start of the cell attachment process, accomplished by the presented method, leads to substantially improved recovery of freshly isolated hepatocytes, and consequently to better overall performance of HF bioreactor.

Interactions between erythromycin, flunixin meglumine, levamisole and plant secondary metabolites towards bovine gastrointestinal motility-in vitro study

Continued ingestion of plant secondary metabolites by ruminants can provoke pharmacological interactions with pharmaceutical agents used in animals. As some drugs and phytocompounds affect smooth muscle activity, the aim of this study was to verify the possible interaction between selected pharmaceutical agents and plant secondary metabolites towards bovine gastrointestinal motility. The interactions between phytocompounds-apigenin, quercetin, hederagenin, medicagenic acid-and medicines-erythromycin, flunixin meglumine and levamisole-were evaluated on bovine isolated abomasal and duodenal specimens obtained from routinely slaughtered cows. The obtained results confirmed the contractile effect of all three drugs used solely. Hederagenin and medicagenic acid (0.001 μM) enhanced the contractile effect of levamisole. Hederagenin additionally increased the impact of erythromycin. Both saponins (100 μM) showed synergistic effects with all tested pharmaceuticals. Apigenin and quercetin (0.001 μM) intensified the contractile response induced by erythromycin and levamisole. Moreover, both flavonoids (100 μM) showed an antagonistic interaction with all tested drugs which in that situation were devoid of the prokinetic effect. To conclude, plant metabolic metabolites such as saponins and flavonoids are potent modifiers of the effect of drugs towards gut motility. The synergy observed between phytocompounds and selected medicines can be beneficial in the treatment of cows with hypomotility disorders.

The effect of glyphosate-based herbicide Roundup and its co-formulant, POEA, on the motoric activity of rat intestine - In vitro study

The study was aimed at evaluating the effect of Roundup, polyoxyethylene tallow amine (POEA) and mixture of glyphosate and POEA in different levels on the motoric activity of jejunum strips. The incubation in the Roundup solutions caused a significant, mostly miorelaxant, reversible reaction of smooth muscle; only in the highest tested dose which is equivalent to the agricultural concentration (1% corresponding to 1.7g glyphosate/L) there was an irreversible disturbance of the spontaneous contractility and reactivity. The incubation in POEA solutions in the range of low doses (0.256; 1.28; 6.4mg/L) resulted in a biphasic muscle reaction (relaxation and contraction); whereas in the range of high doses, i.e. 32; 160 and 800mg/L (agricultural spray concentrations) induced only a miorelaxant, irreversible response. The results indicate very high toxicity of POEA which exceeds the toxicity of the commercial formulations. Besides, it is postulated that glyphosate and POEA may display antagonistic interaction towards the motoric activity of gastrointestinal tract.

Glyphosate affects the spontaneous motoric activity of intestine at very low doses - in vitro study

Glyphosate is an active substance of the most popular herbicides worldwide. Its common use results from the belief that it affects exclusively plants. However, studies on glyphosate and its trade formulations reveal that it causes numerous morphological, physiological and biochemical disturbances in cells and organisms of animals, including mammals. Due to the fact that shortly after oral exposure glyphosate is detected in the highest amount in small intestine, the aim of this study was to evaluate the effect of this compound on the spontaneous motoric activity of intestine under in vitro conditions. The experiments were conducted on rat jejunum strips under isotonic conditions. The strips were incubated in buffered (pH 7.35) and non-buffered (pH 5.2) glyphosate solutions ranged from 0.003 to 1.7 g/L. The results indicate that glyphosate applied in buffered solution affects significantly the spontaneous motoric activity of rat isolated jejunum strips. The muscle response is biphasic (miorelaxation accompanied by contraction). The contraction is observed already at a dose of 0.003 g/L and the first significant biphasic reaction at a dose of 0.014 g/L. The incubation of jejunum strips with glyphosate in non-buffered solution (pH 5.2) results in a different reaction. The smooth muscle undergoes only persistent relaxation, which is stronger than the response to glyphosate solution in pH 7.35. Motility disturbances are also observed after glyphosate removal from the incubation solution. The gathered data suggests that glyphosate impairs gastrointestinal strips' motility at concentration that are noticed in human exposed to non-toxic doses of glyphosate.

Participation of extracellular calcium in α-hederin-induced contractions of rat isolated stomach strips

ETHNOPHARMACOLOGICAL RELEVANCE

The dry extract of Hedera helix leaves, due to its secretolytic and antispasmodic effects, is commonly used to produce pharmaceuticals applied in case of cough and other respiratory symptoms. The results of some in vitro studies as well as the clinical signs of poisoning caused by Hedera helix suggest however strong contractile effect on smooth muscle. In order to clarify the impact of α-hederin (the main active agent of ivy extract) on smooth muscle, the origin of activated calcium involved in α-hederin-induced contraction of gastric smooth muscle preparations was studied.

MATERIALS AND METHODS

The study was carried out on rat isolated stomach corpus and fundus strips, under isotonic conditions. The effect of α-hederin (100 μM) on smooth muscle preparations was measured before and after the treatment with verapamil during the incubation in modified Krebs-Henseleit solution (M K-HS). Besides, the effect of saponin was measured during the incubation of preparation in Ca2+-free modified Krebs-Henseleit solution or Ca2+-free EGTA-containing modified Krebs-Henseleit solution.

RESULTS

The obtained results revealed that the application of verapamil significantly inhibited the reaction evoked by α-hederin. The incubation of stomach strips in calcium-free modified Krebs-Henseleit solution did not change the force of the observed contraction in comparison to the reaction of the preparations incubated in regular incubation solution (M K-HS). In contrary, the replacement of M K-HS by calcium-free chelator-containing solution inhibited totally the reaction to α-hederin.

CONCLUSIONS

The results indicated that α-hederin-induced contraction results from the influx of calcium which is located in intercellular spaces or bound to the outside of the cell membrane. The Ca2+ influx occurs predominantly through voltage-dependent calcium channels of L-type.

Participation of cholinergic pathways in α-hederin-induced contraction of rat isolated stomach strips

The dry extract of Hedra helix leaves and its main active compounds, predominantly α-hederin and hederacoside C, has been traditionally believed to act spasmolytic. However, it has been recently proved that both, the extract of ivy and triterpenoid saponins, exhibit strong contractile effect on rat isolated stomach smooth muscle strips. It turned out that the most potent contractile agent isolated from the extract of ivy leaves is α-hederin. Thus, it seems reasonable to estimate the mechanism of the contractile effect of this saponin. The presented study was aimed at verifying the participation of cholinergic pathways (muscarinic and nicotine receptors) in α-hederin-induced contraction. The experiments were carried out on rat isolated stomach corpus and fundus strips under isotonic conditions. The preparations were preincubated with either atropine or hexamethonium and then exposed to α-hederin. All results are expressed as the percentage of the response to acetylcholine - a reference contractile agent. The obtained results revealed that the pretreatment of isolated stomach strips (corpus and fundus) with atropine neither prevented nor remarkably reduced the reaction of the preparations to α-hederin. Similarly, if the application of saponin was preceded by the administration of hexamethonium, the strength of the contraction of stomach fundus strips induced by α-hederin was not modified. Concluding, it can be assumed that the cholinergic pathways do not participate in α-hederin-evoked contraction of rat isolated stomach preparations.

Hypothermic storage of equine isolated hepatocytes

The aim of the study was to establish the optimal methods for hypothermic storage of equine isolated hepatocytes. Viability of equine isolated hepatocytes after hypothermic storage was dependent on the type of storage medium as well as on the cell density in the storage suspension and the preservation period. Hepatocytes stored at 4 degrees C in Hanks' Balanced Salt Solution (HBSS) and Williams' Medium E (WE) for 24 h showed very low viability, numerous cell membrane blebs, very low attachment rate (11.9 +/- 6.5% and 34.8 +/- 19.1%, respectively) and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) reduction rate (6.4 +/- 3.9% and 25.1 +/- 14.8%, respectively). In contrast, hepatocytes stored in University of Wisconsin Solution (UW) after 24 h of storage at a density of 12.5 x 10(6) cells/ml showed high viability (over 70%), typical and intact morphology, high cell attachment rates and MTT reduction. Our findings clearly demonstrate that UW is a good preservation solution for equine isolated hepatocytes. Hepatocytes harvested from slaughterhouse organs can be stored at 4 degrees C in UW at a density of 12.5 x 10(6) cells/ml for at least 24 h without significant decrease in functional integrity.

Preparation of equine isolated hepatocytes

In this study a detailed description of the equine hepatocyte isolation procedure is presented. Livers were obtained from horses slaughtered at the local slaughterhouse. For blood removal and liver preservation the following steps are suggested: perfusion with the oxygenated HBSS (0-2 degrees C, with continuous flow of 500-800 ml/min for 3-6 min), protection from ischemia injury by flushing with ice-cold University of Wisconsin Solution (UW, flow rate of 500-800 ml/min), and finally immersion of the liver lobe in UW solution (2 degrees C) during its transport to the laboratory. For equine isolated hepatocyte preparation a "three-step" perfusion procedure was elaborated: rewarming, chelating and collagenase perfusion. We found optimal cell yield and viability under the following conditions: rewarming with UW (38 degrees C) for 8-14 min, chelating with calcium free Hanks' Balanced Salt Solution (HBSS, 38 degrees C) supplemented with 1 mM ethylene glycol-bis[beta-aminoethyl esther]-N,N,N'N'-tetracetic acid at the flow rate of 450 ml/min for 6 min and enzymatic digestion with HBSS supplemented with 0.1% collagenase at 38 degrees C and 450 ml/min flow rate for 8-27 min. These conditions consistently generated cell harvests of 21 x 10(6)+/-4.86 cells/g of perfused liver tissue with viability of 82.7%+/-10.2.

Induction of apoptosis and NF-kappaB by quercetin in growing murine L1210 lymphocytic leukaemic cells potentiated by TNF-alpha

Polyphenol quercetin induced apoptosis in proliferating murine L1210 lymphocytic cells. DNA damage, as well as apoptosis and withdrawal from the cell cycle were transient. The above mentioned death promoting activity of quercetin was enhanced by physiological concentrations of TNF-alpha. At the same time, indices of cell viability dropped. However, the extent and tendency of the initially enhanced cell mortality steadily diminished throughout the experiment. After 12 h the G2/M phase reappeared. After 24 h all indices almost returned to control levels indicating either the selection of subpopulation of unaffected leukaemic cells or cells developing resistance to the treatment. A DNA ladder of oligonucleosomes was observed for apoptogenic treatments. We conclude that quercetin unmasked cell death, promoting the activity of TNF-alpha. However, after 12 and 24 h of exposure, surviving cells could complete the cell cycle and finally recover. At the same time, increased NF-kappaB activation was demonstrated by immunoblotting of the immunoreactive RelA/p65 subunit in nuclear extracts. Exposure to TNF-alpha or quercetin was crucial for increased activity of NF-kappaB, which may implicate an increasing resistance to their cytotoxicity.

A simple method for hepatocyte attachment in hollow fibre bioreactors

A new method for hepatocyte attachment in hollow fibre (HF) bioreactors was proposed and verified. A flow of medium with suspended hepatocytes, evoked by transmembrane pressure (TMP), and directed across the membrane into the fibre lumen, has accelerated and improved hepatocyte contact with the HF. It was found that seeding of hepatocytes onto the membrane was optimal at TMP of 50-80 mmHg. Ammonia utilisation and ureagenesis rates in hepatocytes seeded in the bioreactor suggests that the proposed method warrants proper conditions for cell functionality and allows for extended culture of hepatocytes in HF bioreactors. It is speculated that time cutback between introduction of hepatocytes into the bioreactor and the start of the cell attachment process, accomplished by the presented method, leads to substantially improved recovery of freshly isolated hepatocytes, and consequently to better overall performance of HF bioreactor.

The fate of nitrogen from 15N-labeled nitrate after single intravenous administration of Na15NO3 in sheep

The metabolic fate of nitrogen from 15N-labeled sodium nitrate has been investigated in four healthy Polish Merino ewes. 15N-labeled sodium nitrate was administered intravenously at the dosage of 400 mu mol·kg-1 body weight. Blood plasma and urine concentrations of nitrate, ammonia, and urea and 15N enrichment of ammonia and urea were estimated over a 50-h period following 15N-nitrate administration. Nitrate (NO3-) was slowly eliminated from the blood plasma, and the presence of NO3- in the blood plasma above the nitrate "background" was observed for 50 h. 15N enrichment of blood plasma urea already appeared at 15 min and reached the maximum 6 h after 15N-nitrate administration. The urinary excretion of nitrate occured during 50 h after 15N-nitrate injection; the total urine excretion of NO3- was 23.63 ± 2.39% of the administered dose. The mean urinary recoveries of nitrogen as 15N-urea and 15N-ammonia were 14.76 ± 1.32% and 0.096 ± 0.015% of the administered 15N-nitrate dose, respectively. It should be pointed out that in total only 38.49% of the administered nitrate-N was excreted in urine (as nitrate, ammonia and urea nitrogen) during 50 h. The results obtained indicate that sheep are able to store nitrate nitrogen in their body. The fate of the remaining approximately 60% of the 15NO3- administered dose is unknown. The results obtained do not allow one to conclude what fraction of the unrecovered approximately 60% of the 15NO3- dose was utilized by gastrointestinal microorganisms, and (or) metabolized, or stored in sheep tissues.Key words: nitrate, ammonia, urea, metabolism, excretion, sheep.

The fate of nitrogen from 15N-labeled nitrate after single intravenous administration of Na15NO3 in sheep

The metabolic fate of nitrogen from 15N-labeled sodium nitrate has been investigated in four healthy Polish Merino ewes. 15N-labeled sodium nitrate was administered intravenously at the dosage of 400 micromol.kg(-1) body weight. Blood plasma and urine concentrations of nitrate, ammonia, and urea and 15N enrichment of ammonia and urea were estimated over a 50-h period following 15N-nitrate administration. Nitrate (NO3-) was slowly eliminated from the blood plasma, and the presence of NO3(-) in the blood plasma above the nitrate "background" was observed for 50 h. 15N enrichment of blood plasma urea already appeared at 15 min and reached the maximum 6 h after 15N-nitrate administration. The urinary excretion of nitrate occured during 50 h after 15N-nitrate injection; the total urine excretion of NO3(-) was 23.63+/-2.39% of the administered dose. The mean urinary recoveries of nitrogen as 15N-urea and 15N-ammonia were 14.76+/-1.32% and 0.096+/-0.015% of the administered 15N-nitrate dose, respectively. It should be pointed out that in total only 38.49% of the administered nitrate-N was excreted in urine (as nitrate, ammonia and urea nitrogen) during 50 h. The results obtained indicate that sheep are able to store nitrate nitrogen in their body. The fate of the remaining approximately 60% of the 15NO3(-) administered dose is unknown. The results obtained do not allow one to conclude what fraction of the unrecovered approximately 60% of the 15NO3(-) dose was utilized by gastrointestinal microorganisms, and (or) metabolized, or stored in sheep tissues.

Attachment and metabolic activity of hepatocytes cultivated on selected polymeric membranes

Plasma or hormones added to hepatocyte incubation media mask the function of membranes as substrata per se for hepatocyte adhesion. This hypothesis was verified with hepatocyte cultures on various membranes in serum and hormone free medium. Freshly isolated rat hepatocytes were seeded on flat sheet membranes made of Cellulose Acetate (CA), aminated Cellulose Acetate (aCA), polysulfone (PSf) and sulfonated polysulfone (sPSf) and incubated in Hank's Balanced Salts Solutions (HBSS) as well as in William's E medium supplemented with newborn calf serum. It was found that PSf promoted hepatocyte adhesion most effectively. Good properties of PSf as a biomaterial for hepatocyte culture were confirmed in both media cultures. Urea synthesis and ammonia utilization measured in hepatocytes cultured on PSf were higher compared with other membrane cultures. PSf secured longer viability for a higher number of cells seeded on membrane compared with other investigated membranes, which is the reason for higher metabolic activity in PSf culture.

In vitro ammonia utilization and urea synthesis by rat liver after portacaval shunt

BACKGROUND

The objective of this study was to study in vitro ammonia utilization and urea synthesis by the rat liver after portacaval shunt (PCS) in comparison to controls. This study is part of a series of experiments to investigate metabolic derangements in the liver following PCS.

METHODS

Sixteen male Wistar rats weighing 150-230 g were used. PCS was performed on 8 and the rest served as sham-operated controls. The experiments were performed 4 weeks postoperatively. The usually monitored postoperative parameters after PCS like body weight, rise in ammonia levels in the peripheral blood, atrophy of mesenteric fat, atrophy of the liver, etc., were comparable to other PCS series. Liver slices (1 x 2 x 1 mm) were prepared from each rat liver and incubated in Krebs-Henseleit buffer.

RESULTS

After incubation, ammonia utilization in the controls was 162.88+/-20.12 micromol/g dry weight/h while in PCS rats it was 81.35+/-2.64 micromol/g dry weight/h (p < 0.0001). The rate of urea synthesis in controls was 122.54+/-12.93 micromol/g dry weight/h whereas in the PCS group it was 14.99+/-2.21 micromol/g dry weight/h (p < 0.0001).

CONCLUSION

These results indicate a significant decline in the capacity of the liver for ammonia utilization as well as urea synthesis after PCS.

Effect of nitrite on ureagenesis and carbohydrate metabolism in isolated rat hepatocytes

The effect of three NaNO2 concentrations (0.5, 2.0, and 5.0 mM) on 15N-ammonia utilization, ureagenesis, glucose, pyruvate and lactate formation and glycogen breakdown were studied in isolated rat hepatocytes. Nitrite failed to affect the rate of glycogenolysis as well as the lactate and pyruvate formation, but at the same time it markedly increased the glucose formation. It is concluded that the increase in the glucose formation results from the nitrite stimulation of the rate of gluconeogenesis. An increased sodium nitrite concentration caused a significant decrease in the ammonia utilization and urea synthesis; there are strong linear correlations between the nitrite concentration and the amount of utilized ammonia (r = -0.93) and the formed urea (r = -0.96). The observed lower rate of ureagenesis in the presence of nitrite resulted from the diminished incorporation of the added 15N-ammonia into urea, as well as from the diminished urea formation from endogenous nitrogen. It is concluded that the disturbances in carbohydrate and nitrogen metabolism observed in the nitrite-poisoned animals are attributed to the direct effect of nitrite on metabolism.

Effect of propionate on the utilization of nitrogen from 15NH4Cl for urea synthesis in hepatocytes isolated from sheep liver

1. The effect of ornithine (2.0 mM) and propionate (5.0 mM) on the utilization of N from 15NH4Cl (5.0 mM) for urea synthesis in hepatocytes isolated from sheep liver was investigated. 2. The capacity of sheep hepatocytes to utilize [15N]ammonia in the absence of the other exogenous substrates was very low and amounted 132 +/- 37.3 mumol/hr per 1 g dry wt. 3. Ornithine failed to affect the total [15N]ammonia uptake and total urea synthesis, but at the same time it markedly increased the utilization of [15N]ammonia for ureagenesis and diminished the rate of urea synthesis from endogenous sources. 4. Propionate markedly increased total [15N]ammonia utilization and total urea formation; this increase resulted from the rise of ammonia utilization for urea synthesis and it was similar in the presence or absence of ornithine. 5. The capacity of sheep liver cells to utilize ammonia in the presence of propionate (in the presence or absence of ornithine) amounted to 256 mumol/hr per 1 g dry wt, thus being similar to the values in vivo. 6. It is concluded that in sheep hepatocytes both ornithine and propionate stimulate the utilization of ammonia for urea synthesis and these effects take place independently and occur by different mechanisms.