Search PubMed⌕ Search

Biomedical subjects

T H Chiu

Publications and source records attributed to T H Chiu.

At least 127 records · Page 7Linked to original sources
PubMed1984

Radioreceptor assay of benzodiazepines in cerebrospinal fluid during chronic flurazepam treatment in cats.

A radioreceptor assay was used to measure benzodiazepine-like activity in cerebrospinal fluid (CSF) of cats during chronic flurazepam treatment. Benzodiazepine-like activity was measured by the displacement of [3H]flunitrazepam from benzodiazepine receptors in homogenates of rat cerebral cortex. Cats were given 5 mg/kg flurazepam daily, and tolerance was measured by rating several indicators of neurological impairment. CSF was sampled 1 h after flurazepam administration, when drug actions were greatest. Ataxia and muscle relaxation were greatest on the first treatment day, then decreased despite increasing CSF benzodiazepine-like activity. By day 11, CSF activity was 3 times that measured 1 h after the first chronic dose. CSF benzodiazepine-like activity declined slowly after treatment and approached zero by the 10th day after treatment. This residual activity, probably due to active flurazepam metabolites, correlates with the observation that physical dependence is present in these cats up to 7 days after the end of chronic treatment. The rapid loss of drug effect despite increasing active drug levels shows that the nervous system is capable of a rapid and profound adaptation to the presence of benzodiazepines.

Animals↗
PubMed1984

Nontoxic nerve guide tubes support neovascular growth in transected rat optic nerve.

Nontoxic, bioresorbable "nerve guide" tubes were used to bridge the transected optic nerves of adult rats. Nerve guides were fabricated as polymers of synthetic poly D,L-lactates with 2% triethyl citrate added as a plasticizer. The local environment was manipulated further by the addition of the proteins collagen, fibrinogen, and anti-Thy-1 antibody to the nerve guide lumens at the time of operation. Neovascular growth through the nerve guide lumens was quantified with the aid of a computer-controlled microscope. Neovascular growth was greater in the nerve guides to which proteins had been added, compared with initially empty nerve guides. These experiments demonstrated the effectiveness of these nerve guide tubes in supporting and directing neovascular growth in the mammalian central nervous system, and suggested that specific alterations of the local environment within the nerve guide lumen can affect the extent of neovascular growth.

Animals↗
PubMed1984

Nerve regeneration through synthetic biodegradable nerve guides: regulation by the target organ.

The successful regeneration of a multifascicular, complete peripheral nerve through a tubular synthetic biodegradable nerve guide across a gap of 10 mm in the rat sciatic nerve is reported. The importance of the distal nerve as a source of target-derived neuronotrophic factors necessary for the successful regeneration of the proximal regenerating nerve is emphasized. A simplified research model for further investigation into and manipulation of the biological processes of nerve regeneration is described. The potential clinical utilization of this model in the management of peripheral nerve injuries and, ultimately, central nervous system lesions is mentioned.

Animals↗
PubMed1983

Benzodiazepine--specific and nonspecific tolerance following chronic flurazepam treatment.

Rats were given a flurazepam solution as their only water source for 4 weeks. The drug concentration was adjusted so the rats would consume 100-150 mg/kg daily. This treatment is known to cause a reduction in the number of specific benzodiazepine binding sites (receptor down-regulation) and tolerance to the locomotor impairment caused by the injection of a large test dose of flurazepam. Both the tolerance and the receptor down-regulation disappear within 24 hours after the end of chronic treatment. After 4 weeks of flurazepam treatment, rats were tested for locomotor impairment and loss of the righting response caused by pentobarbital, ethanol or diazepam. There was a small tolerance to pentobarbital. This lasted at least 4 days, but had disappeared by 7 days. Rats also had a small tolerance to ethanol, which disappeared between 24 and 48 hours after the end of chronic flurazepam treatment. In contrast, there was a large tolerance to diazepam, but this was gone by 24 hours after the end of chronic treatment. It appears that two types of tolerance develop during benzodiazepine treatment: (1) tolerance specific for benzodiazepines possibly mediated by receptor down-regulation, and (2) nonspecific tolerance, possibly analogous to that which develops during chronic barbiturate treatment.

Animals↗
PubMed1983

Conformational changes in benzodiazepine receptors induced by the antagonist Ro 15-1788.

The binding kinetics of [3H]Ro 15-1788, a selective benzodiazepine receptor antagonist, to synaptosomal membranes of rat cerebral cortices was studied. [3H]Ro 15-1788 binds with high affinity (dissociation constant, 0.53 nM) to a single class of binding sites (maximal binding capacity, 1.97 pmoles/mg of protein). Equilibrium binding was not affected by gamma-aminobutyric acid (GABA), NaCl, pentobarbital, or pretreatment of the membranes at 37 degrees. Association at 0 degrees was identical whether measured in the absence or presence of GABA or bicuculline methiodide or after preincubation of the membranes at 37 degrees. The association rate under pseudo-first order conditions was curvilinear and consisted of a fast component and a slow component. Dissociation at 0 degrees with 1 X 10(-5)M clonazepam was also curvilinear and could best be fitted by two linear exponential components. The dissociation rate was not altered by GABA, NaCl, pentobarbital, or pretreatment of membranes at 37 degrees. The dissociation rate was similar for 0.1, 1, and 10 nM [3H]Ro 15-1788. The ratio of slow to fast dissociation component for 10 nM [3H]Ro 15-1788 was larger than that for 0.1 and 1 nM [3H]Ro 15-1788. In contrast, the dissociation rate for 20 nM [3H]flunitrazepam ( [3H]FNP) was much greater than that for 2 nM [3H]FNP. Using ligand concentrations occupying the same fraction of receptors, the ratio of slow to fast dissociation components was invariably greater for [3H]Ro 15-1788 than that for [3H]FNP. The rate of dissociation for [3H]Ro 15-1788 was faster under pre-equilibrium conditions than under equilibrium conditions. These results, discussed in terms of the cyclic model of interaction between receptors and benzodiazepines, suggest that [3H]Ro 15-1788 is a powerful ligand in inducing conformational changes in the initial, more labile, binary complex. They also suggest that different conformational states deduced from studies of in vitro binding kinetics may not correspond to the distinct pharmacological actions of benzodiazepines. It is speculated that intrinsic activities of benzodiazepines probably are determined by the step beyond the complex formation and conformational changes suggested to occur by these studies of binding kinetics.

Animals↗
PubMed1983

Peripheral nerve repair with bioresorbable prosthesis.

Using the transected sciatic nerve model in adult mice, regeneration of a large bundle of axons organized into the form of a nerve with myelinated and unmyelinated axons, Schwann cells, fibroblasts, collagen, blood vessels, and connective tissue sheaths has been achieved with bioresorbable microtubular guidance channels over gaps of 5 mm in nonimmobilized animals. After 4-6 wks postoperatively, the regenerated nerve cable contains on the order of 40% as many myelinated axons as were measured in the proximal nerve stumps. With the channels used so far in this model, regenerating axons pass into the distal stump in about 3-6 wks postoperatively. The guidance channels used consist of synthetic polyesters and/or polyester composites including glycolic and lactic acid polymers, and polyesters derived from Krebs Cycle dicarboxylic acids. Inflammatory response to these materials has been minimal. Biodegradation/resorption rates can be controlled so as to be compatible with axon growth rates.

Animals↗
PubMed1982

Nature of functional tolerance produced by chronic flurazepam treatment in the cat.

Cats were treated once daily for 35 days with flurazepam (FZP). Different groups received 2, 5 or 20 mg/kg per day. A fourth group was started at 20 mg/kg per day, then the dose was increased to 30, and finally 40 mg/kg per day. Muscle relaxation, ataxia, and other measures of neurological impairment were used to measure drug actions. Tolerance developed rapidly, and no FZP effects were seen after 2-3 weeks of treatment with 2 or 5 mg/kg. Doses of 2-100 mg/kg FZP were injected i.p., 48 h after the last dose of chronic treatment with 2 or 5 mg/kg, and peak FZP effects were recorded. There was an approximate 10-fold shift to the right of the dose-response curve, indicating a large degree of functional tolerance after 5 weeks of FZP treatment. The pattern of tolerance, as measured by dose-response analysis, suggests that it may be different from the functional tolerance developed during barbiturate administration.

Animals↗
PubMed1982

An antagonist-induced benzodiazepine abstinence syndrome.

Cats were treated for 35 days with flurazepam, 5 mg/kg per day. The drug was administered through a gastric fistula. Ro15-1788, a benzodiazepine antagonist, caused an abstinence syndrome when administered through the gastric fistula 24 h after the last dose of chronic treatment. Abstinence signs included increased muscle tone, tremor, piloerection, pupillary dilation, panting, and excessive salivation. Neither convulsions nor delirium was seen. Severity of abstinence was similar after Ro15-1788 doses of 2-100 mg/kg, but lasted longer (8-10 h) after the higher dose. Readministering Ro15-1788 a week after the end of chronic treatment precipitated an attenuated abstinence syndrome, but was inactive after 2 weeks.

Animals↗
PubMed1982

Comparison of the kinetics of [3H]diazepam and [3H]flunitrazepam binding to cortical synaptosomal membranes.

[3H]Diazepam and [3H]flunitrazepam ([3H]FNP) binding to washed and frozen synaptosomal membranes from rat cerebral cortex were compared. In Tris-citrate buffer, gamma-aminobutyric acid (GABA) and NaCl both increased [3H]diazepam binding more than [3H]FNP binding. GABA and pentobarbital both enhanced this effect of NaCl. Because of the extremely rapid dissociation of [3H]diazepam in the absence of NaCl and GABA, the Bmax (maximal binding capacity) was smaller by the filtration assay than by the centrifugation assay. [3H]FNP, which dissociates more slowly, had the same Bmax in both assays. [3H]Diazepam association had two components, and was faster than [3H]FNP association. [3H]Diazepam dissociation, which also had two components, was faster than that of [3H]FNP, and also had a greater fraction of rapidly dissociating species. [3H]FNP dissociation was similar when initiated by diazepam, flunitrazepam, clonazepam, or Ro15-1788, which is a benzodiazepine antagonist. [3H]Diazepam dissociation with Ro15-1788, flunitrazepam, or clonazepam was slower than with diazepam. GABA and NaCl, but not pentobarbital, increased the percentage of slowly dissociating species. This effect of NaCl was potentiated by GABA and pentobarbital. The results support the cyclic model of benzodiazepine receptors existing in two interconvertible conformations, and suggest that, distinct from their binding affinity, some ligands (like flunitrazepam) are better than others (like diazepam) in inducing the conversion of the receptor to the higher-affinity state.

Animals↗
PubMed1982

Biosynthesis of glucosyl monophosphoryl undecaprenol and its role in lipoteichoic acid biosynthesis.

A glucophospholipid was detected in an incubation mixture containing UDP-glucose, MgCl2, ATP, and a particulate enzyme prepared from Streptococcus sanguis. The synthesis of this lipid was inhibited strongly by UDP and moderately by UMP. The molar ratio of glucose to phosphate in the purified lipid was found to be 1:1. Glucose and glucose 1-phosphate were released by mild alkaline hydrolysis of the glucophospholipid. The lipid produced by mild acid degradation of the purified lipid yielded a thin-layer chromatographic profile similar to that of acid-treated undecaprenol. One of the minor components exhibited the same mobility as untreated undecaprenol. To characterize further the lipid moiety of the glucophospholipid, a polyisoprenol was purified from the neutral lipid of S. sanguis. The polyisoprenol was converted in the presence of ATP, UDP-glucose, and the particulate enzyme into a lipid which exhibited the same thin-layer chromatographic mobility as the glucophospholipid. The structure of the polyisoprenol was determined by nuclear magnetic resonance and mass spectrometry to be an undecaprenol with an internal cis-trans ratio of 7:2. These results indicate that the glucophospholipid is glucosyl monophosphoryl undecaprenol. The glucosyl moiety of the glucophospholipid was shown to be incorporated in the presence of the particulate enzyme into a macromolecule which was characterized as a lipoteichoic acid by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and DEAE-cellulose column chromatography. This result indicates that glucosyl monophosphoryl undecaprenol is the direct glucosyl donor in the synthesis of lipoteichoic acid.

Carbon Radioisotopes↗
PubMed1982

Kinetics of [3H]flunitrazepam binding to membrane-bound benzodiazepine receptors.

The kinetics of [3H]flunitrazepam binding to synaptosomal (P2) membranes from rat cerebral cortex was studied. The pseudo-first order association at 0 degrees was curvilinear and the association rate was increased with increasing concentrations of ligand. The association curve was resolved best as two linear exponentials, representing a fast and a slow component. The percentage of each association component varied with the ligand concentration. Association was slightly decreased in the presence of gamma-aminobutyric acid. Dissociation at 0 degrees, whether equilibrium binding had occurred at 0 degrees or 37 degrees, was also biphasic. The dissociation of the complexes was more rapid at higher concentrations of ligand. Dissociation was slower in the presence of gamma-aminobutyric acid, and this effect was more pronounced at higher concentrations of ligand. Prolonged preincubation at 37 degrees either in the presence or in the absence of [3H]flunitrazepam also decreased the dissociation rate. Dissociation was faster before equilibrium than after equilibrium had been reached. These results are discussed in terms of one homogeneous type of benzodiazepine receptor with two interconvertible conformations.

Animals↗
PubMed1981

Regional specificity of benzodiazepine receptor down-regulation during chronic treatment of rats with flurazepam.

[3H]Flunitrazepam binding was studied in synaptosomal membranes from rat brain following 4 weeks of chronic treatment with 100-150 mg/kg/day flurazepam. At 12 h after the end of treatment, the brain was removed and dissected into 8 areas: cerebral cortex, hippocampus, cerebellum, corpus striatum, hypothalamus, midbrain-thalamus, medulla-pons, and olfactory bulbs. Membranes from each area were extensively 'washed', and saturation binding studies performed. Chronic flurazepam treatment caused a reduction in the apparent number of binding sites (Bmax) that was confined to the cerebral cortex, hippocampus, and medulla-pons, with a possible smaller loss in the olfactory bulbs. The binding constant (KD) was unchanged in all areas studied.

Animals↗
PubMed1981

Tolerance during chronic benzodiazepine treatment associated with decreased receptor binding.

Studies were performed to evaluate the time course and possible significance of changes in specific benzodiazepine binding that occur chronic treatment. Rats were offered flurazepam in a saccharin solution as their only fluid supply. Each rats consumed 100-150 mg/kg daily. Such treatment produced no change in the binding constant (KD) of specific [3H]flunitrazepam binding. Maximal binding capacity (Bmax) was reduced by about 20% after 4 or 8 weeks of treatment, but not by 2 weeks or less. Bmax returned to control within 24 h after the end of chronic treatment. Rats were tested for susceptibility to flurazepam by injecting 20-200 mg/kg i.p., and assessing locomotor impairment. Dose-response analysis showed tolerance only after treatments and at times when Bmax was reduced. The results suggest that the reduced Bmax is an adaptive change in response to chronic benzodiazepine treatment, and that the mechanism for tolerance is a reduction of receptors.

Animals↗
PubMed1981

3H-methyl scopolamine binding to dispersed pancreatic acini.

Maximal amylase release occurred with 10(-5) M carbachol and slightly greater than half maximal response occurred with 3 x 10(-7) M carbachol in dispersed pancreatic acini. The preparation released more than 45% of its initial amylase content after 60 min of maximal carbachol stimulation. Electron microscopy revealed depletion of zymogen granules and the presence of secretory material in the ductules after carbachol stimulation. At 37 degrees C, maximal binding of methyl scopolamine occurred in about 45 min with 3 x 10(-10) M 3H-methyl scopolamine. The dissociation constant for 3H-methylscopolamine was 6.8 x 10(-10) M and saturation occurred at 109 pm/g protein. The I.C. 50 for 3H-methylscopolamine inhibition of carbachol-induced amylase secretion was 7 x 10(-10) M.

Amylases↗
PubMed1981

Endogenous modulator of benzodiazepine binding in rat cortex.

Benzodiazepine binding sites, solubilized with 1% digitonin, were used to study specific [3H]flunitrazepam ([3H]FNP) binding. Specific binding increased nonlinearly with increasing amounts of digitonin extract in the assay. Specific binding was increased, and the relationship to amount of extract became linear, in the presence of 2% polyethylene glycol 6000 (PEG). Heat treatment destroyed binding activity of the extract, but not ability to inhibit [3H]FNP binding. Kinetic analysis showed inhibition to be noncompetitive. The inhibitory activity was sensitive to trypsin. Extracts of repeatedly frozen, thawed, and washed membrane preparations still possessed inhibitory activity. It is suggested that digitonin solubilizes a membrane protein that inhibits benzodiazepine binding. PEG apparently removes this substance from the binding sites.

Animals↗
PubMed1981

Age-dependent changes in the myocardial adenylate cyclase of normotensive and spontaneously hypertensive rat.

The activity of myocardial adenylate cyclase from two age groups (10-11 and 18-19 weeks old, respectively) of male spontaneously hypertensive rats (SHR) and their age-matched normotensive Wistar-Kyoto rats (WKY) was examined. Stimulation of the enzyme by isoproterenol and 5'-guanylyl-imidodiphosphate (GMP-PNP) was decreased for both SHR and WKY at the older age. In addition, decreased sensitivity of the enzyme to NaF was also found for older SHR. Except for showing subsensitivity to isoproterenol, the enzyme from SHR at 10-11 weeks of age was activated by GMP-PNP alone, or in combination with isoproterenol, and NaF to the same extent as that from the same age group of WKY. Stimulation of the enzyme by these activators was considerably lower from SHR than from WKY at 18-19 weeks of age. These data indicate that myocardial adenylate cyclase from SHR initially demonstrates a selective decrease in response to isoproterenol, and then a generalized decrease in sensitivity to various activators at a later hypertensive stage.

Adenylyl Cyclases↗