Qualitative patterns of biliary bile acids affect cyclosporine intestinal absorption in liver transplant recipients.
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Adult↗
Biomedical subjects
A Nistri
Publications and source records attributed to A Nistri.
Membrane potential oscillations of neonatal rat spinal motoneurons evoked by electrical stimulation of dorsal root fibres.
Intracellular recording from lumbar motoneurons of the neonatal rat isolated spinal cord bathed in standard saline solution was used to study membrane potential oscillations which accompanied the decay phase of excitatory postsynaptic potentials (EPSP) induced by single electrical pulses to an adjacent dorsal root. About 60% of motoneurons displayed rhythmic oscillations of 10 +/- 2 mV maximal amplitude and 7 +/- 0.5 Hz frequency. Ability to generate oscillations could not be correlated to the cell membrane properties or to the age of the preparation (5-13 days). The oscillation frequency was independent of membrane potential (-100 to -45 mV) or of the intensity of dorsal root stimuli. The oscillation amplitude was linearly related to the cell potential within the same voltage level. Fast Fourier transform analysis showed that the power spectrum of oscillations peaked at approximately 8 Hz. Electrically evoked activities and spontaneous events displayed similar cut-off frequencies. When the cell membrane potential was steadily depolarized, a hyperpolarizing pulse applied during the decay phase of the EPSP promptly revealed the presence of oscillatory behaviour. Pharmacological block of neurokinin-1 or N-methyl-D-aspartate receptors depressed the decay phase of the EPSP and the associated oscillatory responses. It is suggested that rhythmic oscillations were probably due to summated synaptic potentials generated at the premotoneuron level and are perhaps of functional relevance to motoneuron behaviour.
Animals↗
An NK1 receptor-dependent component of the slow excitation recorded intracellularly from rat motoneurons following dorsal root stimulation.
Intracellular recording from lumbar motoneurons of the neonatal rat spinal cord in vitro was used to study how recently developed non-peptide antagonists such as SR-140333 and SR-48698, known to block distinct subtypes of tachykinin receptors peripherally, might affect synaptic transmission elicited by electrical stimulation of dorsal root fibres. SR-140333 (1 microM) preferentially antagonized responses mediated by an exogenously applied agonist acting on the NK1 receptor subclass, while SR-48968 (0.5 microM) preferentially reduced responses mediated by an exogenously applied agonist acting on the NK2 receptor subclass. SR-48968 did not affect fast or slow excitatory postsynaptic potentials (EPSPs) or 'wind-up' responses induced by repetitive, low-frequency stimulation (mimicking certain types of nociceptive input); binding studies using this radiolabelled ligand disclosed specific binding activity (21 fmol/mg protein) selectively displaced by an NK2 receptor agonist. SR-140333 reduced the late component of fast and slow EPSPs, and of wind-up. Pharmacological block of ionotropic glutamate receptors abolished all dorsal root-evoked EPSPs. In comparison to glutamate receptor blockers, SR-140333 was a weaker antagonist of slow synaptic responses, though it displayed preferential antagonism towards some components of the wind-up phenomenon. The present results provide evidence obtained with a novel NK1 antagonist that a neuropeptide (presumably substance P), although not directly released by primary afferents onto motoneurons, is a neurotransmitter (acting via NK1 receptors) in the pathway mediating slow synaptic responses of motoneurons, and is presumably involved in signalling nociceptive inputs from the periphery.
Afferent Pathways↗
Desensitization of AMPA receptors limits the amplitude of EPSPs and the excitability of motoneurons of the rat isolated spinal cord.
Intracellular recording was used to study the effect of cyclothiazide, a selective blocker of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) receptor desensitization, on lumbar motoneurons of the rat isolated spinal cord. Cyclothiazide (25 microM) enhanced the responses to AMPA in a tetrodotoxin-insensitive fashion, without affecting those produced by N-methyl-D-aspartate or gamma-aminobutyric acid. Excitatory postsynaptic potentials (EPSPs) evoked by dorsal root stimulation were strongly potentiated in amplitude while paired-pulse depression (produced by applying pairs of pulses at 2 s interval) of the EPSP was decreased. In the presence of cyclothiazide the frequency of spontaneous synaptic events was greatly increased and network-driven bursting activity developed with eventual loss of electrical excitability. The present results suggest that pharmacological block of AMPA receptor desensitization led to strong excitation of motoneurons and indicate a physiological role of desensitization in protecting these nerve cells from overactivity.
Animals↗
Enhancement of NMDA receptor mediated synaptic potentials of rat hippocampal neurones in vitro by thyrotropin releasing hormone.
The effects of thyrotropin releasing hormone (TRH) on excitatory postsynaptic potentials (EPSPs) evoked by electrical stimulation of Schaffer collaterals on CA1 neurones of the adult rat hippocampal slice preparation were investigated using intracellular recording under current clamp conditions. At resting membrane potential and in the presence of extracellular Mg2+, TRH (10-20 microM) largely potentiated NMDA receptor-mediated EPSPs while leaving those mediated by non-NMDA receptors unaffected. This phenomenon had a brief duration (approximately 2 min) and was not accompanied by changes in resting membrane potential or input conductance. It is suggested that TRH provided a transient upregulation of synaptic responses due to NMDA receptor activation.
Action Potentials↗
Lamellar bodies coexist with vesicles and micelles in human gallbladder bile. Ursodeoxycholic acid prevents cholesterol crystal nucleation by increasing biliary lamellae.
The aggregative forms of lipids in human gallbladder bile and their relation to cholesterol crystallization are controversial. Using combined chemical, gel-chromatographic, optical/electron microscopic and quasielastic light-scattering methods, we investigated this issue in native gallbladder bile obtained from nine untreated cholesterol gallstone patients and eight cholesterol gallstone patients treated for 1 week with 600 mg/day of ursodeoxycholic acid. Bile obtained at cholecystectomy was ultracentrifuged for 2 h at 150,000 g to obtain isotropic samples. The conventional cholesterol crystal observation time was 3.1 +/- 4.1 (SD) days in controls and 19.0 +/- 1.9 days in the ursodeoxycholic acid-treated group (p < 0.001). Bile was analyzed by high-resolution gel-chromatography using 7 mM sodium taurocholate in the elution buffer. Biliary lipids eluted in four chromatographic zones: zone #I, corresponding to the column void volume, contained only minimal amounts of lipids; zone #II (apparent m.w. 100-220 kDa) comprised 29.1 +/- 12.4% of biliary cholesterol in the untreated group and 8.3 +/- 4.3% in the ursodeoxycholic acid-group (p < 0.001). At negative staining electron microscopy, this region was composed of roundish vesicles ranging from 7 to 20 nm in diameter. Zone #III (apparent m.w. 50-100 kDa) carried 59.1 +/- 2.1% of cholesterol in untreated patients and 81.2 +/- 9.5% in ursodeoxycholic acid-rich biles, respectively (p < 0.001). At negative staining electron microscopy, this region was composed of lamellar stacks of variable length, usually with 5 nm interspaces and up to 30 nm in width. In ursodeoxycholic acid-rich biles, lamellae often appeared in the form of concentric fingerprint-like images. Quasielastic light-scattering measurements in this region were compatible with the size estimates obtained at electron microscopy. Zone #IV (apparent m.w. 6-50 kDa) carried 11.8 +/- 9.4% and 11.6 +/- 9.0% of cholesterol, respectively (not significant). Since this region comprised a considerable fraction of endogenous bile salts and had no distinct morphological structures, it was interpreted as mixed micelles. The cholesterol crystal observation time showed a significant inverse correlation (r = -0.85, p < 0.001) with percent cholesterol carried by vesicles (zone #II) and a direct correlation (r = 0.86, p < 0.001) with percent cholesterol carried by lamellar bodies (zone #III). Vesicles and lamellae identical to those observed in isolated gel-chromatographic fractions were observed also on direct electron microscopic examination of unfractionated isotropic native biles. Similar findings were observed also in matched model biles.(ABSTRACT TRUNCATED AT 400 WORDS)
Bile↗
Effects of RP 67580 on substance P-elicited responses and postsynaptic potentials of motoneurones of the rat isolated spinal cord.
The effect of RP 67580, a recently developed antagonist selective for the NK1 tachykinin receptors of peripheral tissues, was studied with intracellular recording from motoneurones of the rat isolated spinal cord. In the presence of RP 67580 (1-2 microM), membrane depolarization induced by the putative transmitter substance P (SP) was either unchanged or enhanced (an effect prevented by tetrodotoxin; TTX). Neither short nor long excitatory synaptic potentials (EPSPs) were antagonized by RP 67580. Sustained synaptically evoked depolarizations (mimicking noxious stimuli and thus presumed to be at least partly mediated by SP) were also insensitive to RP 67580. These data suggest the existence of a pharmacologically distinct NK1 receptor population insensitive to RP 67580) in the neonatal rat spinal cord.
Animals↗
Dissolution of human cholesterol gallstones in bile salt/lecithin mixtures: effect of bile salt hydrophobicity and various pHs.
BACKGROUND: Unconjugated bile salts currently available for gallstone dissolution are poorly effective. We evaluated in vitro the litholytic potency of taurine-amidated bile salts against human cholesterol gallstones. METHODS: Seventy radiolucent gallstones with similar size and composition (cholesterol content, 70.1 +/- 0.9%) from a single patient were incubated in model biles composed of 100 mM of either taurochenodeoxycholate (TCDC), taurocholate (TC), taurohyodeoxycholate (THDC) or tauroursodeoxycholate (TUDC) and of 45 mM egg yolk lecithin in saline buffered with tris/HCl (at pHs 7 and 8) or phosphate (at pHs 4 and 6). Biles (total lipids, 10 g/dl; cholesterol saturation, 99%) were incubated at 37 degrees C for 40 days. Gallstones were periodically weighed and returned to the dissolution vials, and the biliary cholesterol concentration was monitored. RESULTS: Model biles remained optically clear during the initial 48 h of incubation. Then, biles containing THDC and TUDC, but not those with TC and TCDC, became progressively turbid until, after several days, a white precipitate surrounded the residual stone. Abundant liquid crytalline droplets were observed at polarizing microscopy in biles containing TUDC and THDC. Gallstone dissolution was closely related to cholesterol solubilization and decreased in the order TCDC > THDC > or = TC > TUDC, being highest at pH 8. At the physiologic pH of 7 THDC was more litholythic than TC. CONCLUSIONS: In vitro, the litholytic potency of bile salts on cholesterol gallstones primarily depends on their hydrophobicity. THDC is a new potential gallstone-dissolving agent, deserving in vivo studies.
Cholagogues and Choleretics↗
N-ethyl-tauroursodeoxycholic acid, a novel deconjugation-resistant bile salt analogue: effects of acute feeding in the rat.
The purpose of this study was to investigate the physicochemical/biological properties and the effects of acute administration of N-ethyl-tauroursodeoxycholic acid in bile-fistula rats. In vitro determination of high-performance liquid chromatography mobility, octanol/ water partitioning, cholesterol solubilizing capacity, and sensitivity to enzyme deconjugation by bacteria and cholylglycine-hydroxylase were performed. In vivo determination of the following was also performed: (1) maximum secretory rate (SRmax) and choleretic/secretory properties during intravenous (IV) administration; (2) site/ extent of absorption, effects on bile flow, lipid secretion, and biotransformations after intraduodenal infusion. N-ethyl-tauroursodeoxycholate has a lipophilicity slightly higher than tauroursodeoxycholate, close to taurocholate, and similar cholesterol solubilizing capacity. Deconjugation of N-ethyl-tauroursodeoxycholate was 3.4 +/- 2.1% after 72 hours, that of tauroursodeoxycholate was 100% after 24 hours. During IV infusion of 300 nmol/min/ 100g, biliary secretion of N-ethyl-tauroursodeoxycholic and tauroursodeoxycholic acids averaged 185 +/- 76 (standard deviation) nmol/min/100 g and 221 +/- 77 nmol/min/ 100 g (not significant). Increasing infusion rates caused progressive enhancement of bile flow and bile salt secretion until the SRmax was reached (1,305 +/- 240 nmol/min/ 100 g for N-ethyl-tauroursodeoxycholic acid and 3,240 nmol/min/100 g for tauroursodeoxycholate). The two bile salts were similarly choleretic. IV feeding of N-ethyl-tauroursodeoxycholic promoted a greater lipid secretion than tauroursodeoxycholate. After intraduodenal feeding of 800 mumol, 38.8 +/- 14.0% and 43.4 +/- 12.4% of the two bile salts were recovered in bile. No unconjugated bile salts nor unusual metabolites were detected.(ABSTRACT TRUNCATED AT 250 WORDS)
Animals↗
Sequential changes in serum and biliary bile acids after liver transplantation.
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Adult↗
Electrophysiological interactions between 5-hydroxytryptamine and thyrotropin releasing hormone on rat hippocampal CA1 neurons.
Intracellular recording from CA1 neurons of the rat hippocampal slice preparation was used to examine the possibility of functional interactions between 5-hydroxytryptamine (5-HT) and thyrotropin releasing hormone (TRH), which act as cotransmitters in other areas of the central nervous system. 5-HT (30 microM) elicited complex effects consisting of biphasic changes in membrane potential and a strong depression of the afterhyperpolarization (AHP) following a spike burst. TRH (10 microM) did not alter membrane potential or input conductance but it produced a partial block of the AHP. Under single-electrode voltage clamp, 5-HT and TRH both reduced the amplitude of voltage-activated total K+ currents. When the two substances were co-applied, their actions were occluded. The voltage-activated K+ current remaining in Ca(2+)-free solution lost its sensitivity to 5-HT and TRH, suggesting that the K+ current modulated by TRH and 5-HT was Ca(2+)-dependent, although TRH itself did not depress high-threshold voltage-activated Ca2+ currents. When a relatively small concentration (5 microM) of 5-HT was co-applied with an equimolar amount of TRH, the degree of block of the spike AHP was the sum of the two individual effects of these drugs. It is suggested that in hippocampal pyramidal cells 5-HT and TRH influenced neuronal excitability by depressing a Ca(2+)-dependent K+ current, a phenomenon perhaps mediated through a common intracellular second messenger pathway.
Animals↗
Serum fractions from amyotrophic lateral sclerosis patients depress voltage-activated Ca2+ currents of rat cerebellar granule cells in culture.
Whole-cell patch clamp recording from rat cerebellar granule cells in culture was used to study the effect of immune protein fractions extracted from the serum of amyotrophic lateral sclerosis (ALS) patients on voltage-activated Ca2+ currents. The inward currents, carried by Ba2+, were induced by depolarizing step commands positive to -50 mV and showed typical voltage-dependent inactivation. Application of immunoprotein fractions obtained from the serum of ALS patients produced a strong depression of the inward current amplitude without changing its threshold potential at which the maximum was attained, or its time course. These data support the hypothesis that the serum of ALS patients contains an immunoprotein capable of interacting with high threshold Ca2+ channels of central neurones.
Adult↗
Modulation by TRH of NMDA-elicited responses of CA1 neurones of the rat hippocampal slice preparation.
Intracellular recording from CA1 neurones of the rat hippocampal slice preparation was carried out to assess the ability of the endogenously-occurring neuropeptide thyrotropin-releasing hormone (TRH) to modulate responses elicited by the excitatory amino acid agonist N-methyl-D-aspartate (NMDA). TRH (5 microM) produced no change in resting membrane potential or input resistance but facilitated on-going synaptic activity. In the continuous presence of the peptide responses to NMDA were selectively enhanced for about 20 min. In approximately 50% of cells the potentiating effect of TRH persisted in tetrodotoxin (TTX) solution and was associated with removal of the apparent voltage-dependent increase in input resistance usually found during the NMDA-induced depolarization. It is suggested that TRH evoked a transient upregulation of NMDA responses which might account for the reported facilitation by this peptide of long term potentiation in the hippocampus.
6-Cyano-7-nitroquinoxaline-2,3-dione↗
Multiple types of tachykinin receptor mediate a slow excitation of rat spinal motoneurones in vitro.
Using intracellular current clamp recording from motoneurones of the neonatal rat spinal cord in vitro, the action of tachykinin receptor agonists was investigated. Test drugs included the endogenously occurring neuropeptide substance P and synthetic compounds, such as substance P methylester (SPMeO), [beta Ala8]neurokinin A4-10 ([Ala]NKA), [MePhe7]neurokinin B ([MePhe]NKB) and senktide. SPMeO and [Ala]NKA were used as selective agonists at NK1 and NK2 receptors, respectively, while [MePhe]NKB or senktide were employed to activate NK3 receptors. In control solution, all compounds produced sustained depolarization with increase in input resistance although at comparable levels of membrane depolarization different patterns of motoneuronal firing were observed dependent on the type of agonist tested. In tetrodotoxin (TTX; 1 microM) solution, the depolarization caused by substance P or SPMeO largely persisted while in the majority of cells the effect of [Ala]NKA, [MePhe]NKB or senktide was blocked. It is suggested that NK1 receptors primarily mediated the actions of substance P on spinal motoneurones and that activation of NK2 or NK3 receptors, predominantly found on interneurones, induced motoneuronal depolarization with different firing patterns.
Animals↗
Non-monotonic decay of excitatory synaptic transmission in the frog optic tectum following repetitive stimulation of the optic nerve in vitro.
The monosynaptic field excitatory postsynaptic potentials (EPSPs) evoked in the optic tectum of the frog (Rana remporaria) in vitro by different patterns of stimulation of the contralateral optic nerve were studied using extracellular recording. Pulse trains at frequencies of less than or equal to 0.033 Hz elicited field potentials of stable amplitude, whereas in the range 0.33-1.0 Hz EPSPs showed a depression in the first few responses subsequent to the first one, followed by a partial recovery and a final decline to a steady level. When the interpulse interval was less than 200 ms, paired-pulse monosynaptic facilitation was found. Decrease in the external Ca2+ concentration, or in the stimulation intensity or application of picrotoxin reversibly produced a monotonically decreasing EPSP amplitude, suggesting that a local neuronal circuit was controlling the development of synaptic fatigue. A simple model based on the combined effects of depletion of excitatory transmitter stores plus activation of a local inhibitory circuit was found to provide a simulation which closely resembled the experimentally observed pattern of synaptic fatigue. The present study suggests that an inhibitory synaptic process contributed to the non-monotonic decay of excitatory transmission in the frog optic tectum, following repetitive stimulation of the optic nerve.
Animals↗
Effect of taurohyodeoxycholic acid, a hydrophilic bile salt, on bile salt and biliary lipid secretion in the rat.
Taurohyodeoxycholic acid is a natural 6 alpha-hydroxylated bile acid with an apparent hydrophilicity intermediate between those of tauroursodeoxycholic and taurocholic acids. We investigated in the rat the hepatobiliary metabolism, choleretic properties, and biliary maximum secretory rate (SRmax) of taurohyodeoxycholic in comparison with these two bile salts. Each compound was infused intravenously, at a rate increased in a stepwise manner from 100 to 300 nmol/min/100 g body wt, in bile salt-depleted bile fistula rats. The three bile salts appeared rapidly starting with the infusion and increased to represent more than 95% of the total bile salts. No apparent biliary metabolites were formed. All the bile salts caused a dose-dependent increase in bile flow and biliary lipid output. The absolute increase in bile flow was lower in rats infused with taurohyodeoxycholic acid, yet the volume of bile formed per nanomole of secreted bile salt was 13.8 nl for taurohyodeoxycholic, 6.4 nl for tauroursodeoxycholic acid, and 10.9 nl for taurocholic. The SRmax values were 1080, 3240, and 960 nmol/min/100 g, respectively. At all infusion rates, taurohyodeoxycholic acid caused a greater (P < 0.001) secretion of biliary lecithin compared to the other bile salts. There were no significant differences in the biliary secretion of cholesterol and proteins. Electron microscopy showed the recruitment of vesicles and lamellar bodies around and within bile canaliculi. In conclusion, taurohyodeoxycholic promotes a biliary lecithin secretion greater than expected from physicochemical predictions, representing a novel secretory property with potential pharmacological relevance.
Animals↗
Oral S-adenosyl-L-methionine (SAMe) administration enhances bile salt conjugation with taurine in patients with liver cirrhosis.
We investigated whether the oral administration of SAMe influences the hepatic availability of sulphur amino acids and the extent of bile salt amidation with taurine in liver cirrhosis. Ten patients with cirrhosis (eight Child-Pugh A and 2 B, aged 48-65 years), were studied before and 2 months after oral SAMe administration (800 mg per day). Bile was obtained using a string-test device (Entero-test), after gall-bladder contraction with caerulein. No significant changes were found in the per cent composition of biliary amino acids, except for an increase in glutamic acid (from 3.7 +/- 0.6% before to 6.1 +/- 1.1% after SAMe, p = 0.003) and taurine from 2.2 +/- 2.3% (range 0.4-6.8) to 7.2 +/- 9.2% (range 0.5-28.1), (NS). HPLC analysis showed a trend towards increased per cent tauroconjugation of all individual bile salts, with a significant rise in taurochenodeoxycholic acid (from 15.0 +/- 9.4% to 25.3 +/- 9.7%, p = 0.05) and a drop in glycocholic acid (from 39.1 +/- 15.3% to 25.3 +/- 9.8%, p = 0.05). These data suggest that in the cirrhotic liver exogenous SAMe is partially metabolized to taurine, which is used for bile salt amidation.
Administration, Oral↗
A study of the barium-sensitive and -insensitive components of the action of thyrotropin-releasing hormone on lumbar motoneurons of the rat isolated spinal cord.
The electrophysiological action of thyrotropin-releasing hormone (TRH) on rat spinal motoneurons was studied in vitro using single-electrode voltage- and current-clamp techniques. In current-clamp conditions TRH elicited a slowly developing depolarization, associated with a large input resistance increase and sustained neuronal firing; the primary metabolites of TRH were ineffective. Under voltage-clamp conditions in the presence of tetrodotoxin, TRH evoked a large inward current (ITRH; peaking at approximately -40 mV) associated with a large input conductance fall. Only 44% of cells displayed ITRH reversal; when the chord conductance values of these cells were plotted against membrane potential, a bell-shaped relation occurred, indicating voltage-dependent block by TRH of a persistent conductance active over a wide range of membrane potentials. ITRH reversal values were shifted to more positive levels in high K+ solution in Nernstian fashion; hence a large proportion of the TRH response is suggested to be mediated by the block of a K+ conductance (IK(T)). IK(T) (and its voltage-dependent block by TRH) was resistant to certain K+ channel antagonists (tetraethylammonium, Cs+, 4-aminopyridine or apamin), but was depressed by Ba2+. The Ba(2+)-resistant fraction of ITRH was attenuated by Cd2+, Mn2+ or Co2+, indicating that it probably involved a Ca(2+)-sensitive inward current. Concomitant application of Ba2+ and Cd2+ induced a near-total block of the response to TRH. It is suggested that suppression of IK(T), associated with the onset of a Ca(2+)-sensitive current, can explain the excitatory effect of TRH on rat spinal motoneurons.
4-Aminopyridine↗