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Biomedical subjects

T L Lee

Publications and source records attributed to T L Lee.

At least 55 records · Page 3Linked to original sources
PubMed1998

High resolution electron microscopy of amorphous interlayers between metal thin films and silicon.

High-resolution electron microscopy of amorphous interlayers (a-interlayer) formed by solid-state diffusion between metal thin films and silicon is reviewed. In this paper, an overview of the development is presented. Pertinent data obtained on the growth kinetics and structure of a-interlayers in polycrystalline metal thin films on single-crystal silicon are reported. For the Ti/Si, Zr/Si, Hf/Si, V/Si, Nb/Si and Ta/Si systems, the growth of a-interlayer was found to follow a linear law in the initial stage. Si atoms were found to be the dominant diffusing species in the solid phase amorphization in the Ti/Si, Zr/Si, and Hf/Si systems. For the Y/Si system, the stability of amorphous interlayer depends critically on the composition of the amorphous films. Auto-correlation function analysis was utilized to determine the structure of the amorphous interlayers. HRTEM in conjunction with the fast Fourier transform were applied to determine the first nucleated crystalline phase. Simultaneous presence of multiphases was observed to occur in a number of refractory metal/Si systems.

Metals↗
PubMed1998

Single vital capacity inhalational anaesthetic induction in adults--isoflurane vs sevoflurane.

PURPOSE: To evaluate whether isoflurane is as suitable as sevoflurane for the single vital capacity breath (VCB) method of inhalational induction in patients premedicated with midazolam. METHODS: A randomised, controlled, double-blind study involving 67 ASA I-II patients aged between 18-50 yr undergoing elective surgery under general anaesthesia. All participants received premedication with 0.03 mg.kg-1 midazolam i.v. Using a primed circle absorber circuit, inhalational induction of anaesthesia was performed with the single VCB method using either isoflurane 3.5% or sevoflurane 7.5% in nitrous oxide 67% in oxygen, representing approximately equivalent MAC-multiples of 3.6 MAC. Isoflurane was compared with sevoflurane in terms of rapidity, efficacy, safety and acceptability of induction. RESULTS: With the single VCB method, sevoflurane produced a faster (45 +/- 21 vs 71 +/- 22 sec, P < 0.01), more successful (100% vs 75.8%, P < 0.01) induction of anaesthesia, with fewer induction-related complications (11.8% vs 84.8%, P < 0.01) than did isoflurane. There was also greater patient acceptability of induction with sevoflurane (76.4% vs 42.4%, P < 0.05). CONCLUSION: In adults given midazolam premedication, isoflurane is not as suitable as sevoflurane for single VCB inhalational anaesthetic induction technique as it is associated with slower, more complicated induction and less patient acceptability.

Adolescent↗
PubMed1998

Stimulatory effect of octopamine on beta 3-adrenoceptors to lower the uptake of [14C]-deoxy-D-glucose into rat adipocytes in vitro.

1. The effect of octopamine on beta 3-adrenoceptors has been studied in isolated adipocytes of Wistar rats using uptake of [14C]-deoxy-D-glucose as the indicator. 2. Octopamine (0.1-1 nmol 1-1) induced a concentration-dependent decrease of [14C]-deoxy-D-glucose uptake into the adipocytes and this inhibition was not influenced by haloperidol at concentrations sufficient to block dopaminergic receptors. 3. Pindolol and propranolol reversed this inhibition of octopamine in a concentration-dependent manner. The effect of octopamine was reduced in the presence of Rp-cyclic AMPS triethylamine, the membrane-permeable antagonist of cyclic AMP (cAMP), indicating the mediation of cAMP in this inhibition. 4. A direct effect of octopamine on beta 3-adrenoceptors was proved using the application of antibodies. In the presence of an antibody for beta 3-adrenoceptors, the actions of octopamine were concentration-dependently reduced in a manner similar to the decrease of BRL37344-induced inhibitions. 5. The same degree of diminished activities for octopamine as that of BRL37344, the well-known specific agonist of beta 3-adrenoceptors, was also obtained in isoprenline-desensitized adipocytes. Insulin-stimulated uptake of [14C]-deoxy-D-glucose into adipocytes was not modified by isoprenaline induced desensitization. 6. These results suggest that octopamine can activate beta 3-adrenoceptors to lower the glucose uptake through an increase of cAMP in rat white adipocytes.

Adipocytes↗
PubMed1998

Gene transfer via pollen-tube pathway for anti-fusarium wilt in watermelon.

In order to obtain transgenic fusarium wilt resistant watermelon plants, squash DNA was introduced into the ovaries of watermelon plants via the pollen-tube pathway. The introduction of foreign genes into ovaries was accomplished using co-transformation with the CaMV35S-GUS as a marker. Transformed watermelon plants contained integrated copies of the GUS activity and the seeds of transformed progeny produced a blue color when stained with 5-bromo-4-chloro-3-indolyl glucuronide, whereas seeds from untransformed control plants did not. Of 200 transformed seedlings, ten were wilt resistant. The presence of the GUS activity in the genome of stable transgenic seedlings was confirmed by Southern blot analysis. Furthermore, the generation of random amplified polymorphic DNA (RAPD) fingerprints using primers with embedded restriction sites showed amplification products unique to these transgenic plants. Primers OPA-1 and OPA-9 gave distinct band patterns of genomic DNA using the polymerase chain reaction.

DNA, Plant↗
PubMed1997

Antinociceptive activity of Channa striatus (haruan) extracts in mice.

Haruan, Channa striatus, is a snakehead fish consumed in many parts of the southeast Asian region. It is believed to promote wound healing, as well as reduce post-operative pain. In an attempt to establish the scientific basis for the alleged pain-relieving benefits of this fish, we studied the antinociceptive effects of whole fillet and mucus extracts from haruan in the mouse using the abdominal constriction and tail flick tests. In the abdominal constriction test, the 30 min fillet extract exhibited concentration-dependent inhibition of the writhing response in the 10-50% concentration range, with 20% as the IC50 value. This activity was not dependent on the duration of extraction, with no significant differences among the extracts obtained at durations of 10, 20, 30, 60, 90 and 120 min (range between 45-54% inhibition at 20% concentration). The mucus extract also showed concentration-dependent inhibition of the abdominal constriction response-at the highest concentration used the average inhibition was 68.9%, while IC50 value was 25%. Neither the fillet extract (30 min, 20%) nor the mucus extract (25%) had any demonstrable effect on the tail flick latency on their own, but significantly enhanced the antinociceptive activity of morphine in this assay. Similarly, low concentrations of the mucus and fillet extract enhanced the effects of morphine in the abdominal constriction test. Collectively, these results suggest a scientific basis for the folklore practice of eating haruan fish in the post-operative period for pain relief: Haruan extracts have antinociceptive activity and enhance the activity of other antinociceptive agents.

Analgesics↗
PubMed1997

Autoantigen components recognizable by scleroderma sera are exported via ectocytosis of fibroblasts.

Previously, we have demonstrated that ectocytosis, a unique cell trafficking process to export a specific subset of cellular proteins in the form of membrane vesicles, can be triggered from human skin fibroblasts cultured in a three-dimensional collagen lattice upon stress relaxation. The same culturing system was employed in the present study using fibroblasts isolated from patients with systemic sclerosis (SSc). To see whether any putative intracellular autoantigens causing SSc might escape out of cells by way of ectocytosis, the same stress-relaxation method was used to induce a synchronized ectocytosis among cultured cells. Membrane vesicles released by scleroderma fibroblasts were subsequently isolated, resolved on SDS-PAGE and immunoblotted with sera from 89 patients with various autoimmune diseases and 11 normal volunteers. Three major polypeptides with apparent mol. wts of 12-14, 32-34 and 70-80 kDa are prominent bands on both SDS-PAGE and immunoblots. The 32-34 kDa polypeptide has been further identified as a member of the annexin protein family, while the 70-80 kDa protein has been shown to be topoisomerase I, as judged by its reactivity to patients' sera and a rabbit polyclonal antibody, and as also judged by a functional assay. In conclusion, our results suggest that ectocytosis might be one of the potential pathways for cells to export intracellular antigens and subsequently cause autoimmune reactions.

Animals↗
PubMed1997

Oxygen consumption--a comparison between calculation by Fick's principle and measurement by indirect calorimetry.

Oxygen consumption values calculated by Fick's principle (cVO2) were compared to simultaneously obtained values measured by indirect calorimetry (mVO2) in two groups of patients; post-coronary artery bypass graft (post-CABG) and septic shock. In both groups of patients, oxygen consumption values derived using indirect calorimetry were higher than that from Fick's principle. Whilst the bias obtained between the two methods of measurement were of acceptable amount clinically, the limits of agreement were wide: -57 to 51 ml.min-1.m-2 in the post-CABG group and -101 to 67 ml.min-1.m-2 in the group of septic patients; indicating that significant differences exist between paired individual values such that cVO2 and mVO2 were not interchangeable in this study.

Adult↗
PubMed1996

Comparison of isoproterenol with BRL37344 in activation of beta 3-adrenoceptors to inhibit the uptake of [14C]deoxy-D-glucose and translocation of glucose transporter (GLUT4) to membrane fraction in rat adipocytes.

In an attempt to understand the role of beta 3-adrenoceptors in the regulation of glucose uptake, the effect of isoproterenol was compared with BRL37344 in isolated white adipocytes of the rat using [14C]deoxy-D-glucose as an indicator. In the presence of BRL37344, the specific agonist of beta 3-adrenoceptors, spontaneous uptake of [14C]deoxy-D-glucose (glucose uptake) into adipocytes was markedly attenuated. Similar concentration-dependent inhibition of glucose uptake was also observed in the samples treated with isoproterenol, an agonist for all kinds of beta-adrenoceptors. Action of BRL37344 was blocked by propranolol at concentrations sufficient to abolish the activity of isoproterenol. Pindolol reversed BRL37344-induced inhibition more effectively than propranolol. Moreover, unlike the action of isoproterenol, BRL37344 did not modify the insulin-stimulated glucose uptake. Translocation of glucose transporter (GLUT4) from cytosol to membrane stimulated with insulin was reduced by isoproterenol but not by BRL37344. Combination with the findings that isoproterenol prolonged the time for insulin to reach maximum stimulation of glucose uptake, leads to the conclusion that delay of insulin action by isoproterenol can be considered as one of the mechanisms for this inhibition. The results obtained suggest that BRL37344 decreased the spontaneous uptake of glucose via an activation of beta 3-adrenoceptors while the insulin stimulated glucose uptake was inhibited by isoproterenol but not by BRL37344.

Adipocytes↗
PubMed1996

A thromboelastography study on the in vitro effects of L-arginine and L-NG-nitro arginine methyl ester on human whole blood coagulation and fibrinolysis.

The effects of L-arginine and L-NG-nitro arginine methyl ester (L-NAME) on human blood coagulation and fibrinolysis were studied in vitro using computerized thromboelastography and native whole blood. L-Arginine (8-80 microM) prolonged the split point (SP), reaction time (R) and biKoatugulierung time (K); and diminished the angle (alpha), maximum amplitude (MA) and TEG index. L-NAME (0.5-50 microM) shortened SP, R and K and increased alpha, MA and the TEG index in a concentration-dependent manner. Neither L-arginine nor L-NAME had any effect on clot lysis. SP and R indicated the initiation of fibrin-strand formation, therefore L-arginine delayed, while L-NAME promoted the processes leading to fibrin formation. K and alpha reflect the rate of clot formation and involve fibrin build-up and platelets. Thus, L-arginine inhibited and L-NAME enhanced the rate of clot formation. MA (clot strength) involves the integrity of fibrin strands and platelet aggregation, and again L-arginine was inhibitory, while L-NAME enhanced this interaction. The TEG index indicates the coagulability of the sample; L-arginine was anticoagulant while L-NAME had procoagulant effects. These results are consistent with the inhibitory effects of NO on platelet function and of the platelet-aggregating properties of NOS inhibitors. In addition, NO may play an inhibitory role in the process leading to fibrin formation and also on the interactions between platelets and fibrin. Such effects may be important when considering the clinical use of drugs that affect the NO-cGMP pathway.

Adult↗
PubMed1996

Role of nitric oxide in the induction and expression of morphine tolerance and dependence in mice.

1. The possible involvement of nitric oxide (NO) in the induction and expression of morphine tolerance and dependence was studied in mice. A two-day repeated injection regimen was used to induce morphine tolerance and dependence. Tolerance was assessed by the tail flick test and physical dependence by naloxone challenge, on the third day. 2. Two days pretreatment with L-arginine (20 mg kg-1, twice daily) or D-NG-nitro arginine methyl ester (D-NAME, 20 mg kg-1, twice daily) alone had no effect on subsequent morphine antinociception. L-NG-monomethyl arginine (L-NMMA, 10 mg kg-1, twice daily) for two days led to a slight increase (not statistically significant) in morphine antinociception; while L-NG-nitro arginine methyl ester (L-NAME, 10 mg kg-1, twice daily) for two days led to attenuation of morphine analgesia. None of the animals treated with these drugs alone showed signs characteristic of the opioid withdrawal syndrome upon naloxone challenge. 3. Induction phase L-arginine slowed the development of opioid tolerance and physical dependence, while L-NAME and L-NMMA led to a higher degree of tolerance but had no effect on the development of physical dependence. 4. L-Arginine and D-NAME had no effect on the expression of morphine tolerance and physical dependence. Expression phase L-NAME and L-NMMA, on the other hand, attenuated morphine tolerance and reduced the incidence of withdrawal signs. 5. NO may, therefore, play a role in both phases of morphine tolerance and dependence: elevation of NO levels during the induction phase delays the development of opioid tolerance/dependence, while inhibition of NO synthase accelerates the development of tolerance. Inhibition of NO attenuates the expression of both tolerance and physical dependence.

Animals↗
PubMed1995

Anticoagulant effects of Pseudechis australis (Australian king brown snake) venom on human blood: a computerized thromboelastography study.

The crude venom of Pseudechis australis exhibited a dose-dependent anticoagulant action on human blood in vitro using computerized thromboelastography. Clot progress parameters (K and alpha) were affected at low dose levels which had no effect on onset of coagulation parameters (SP, R). At high dose levels there was total anticoagulant effect, but in all cases there was no evidence of fibrinolytic activity. These results generally agree with the known effects of this venom on coagulation in vivo, and further support our earlier suggestion that TEG may be a useful, one-step tool in the diagnosis and monitoring of the progress of envenomation patients.

Anticoagulants↗
PubMed1995

Effects of the platelet-activating factor receptor antagonist WEB 2086 on whole blood coagulation and fibrinolysis in a thromboelastography assay.

The effects of WEB 2086 on human blood coagulation and fibrinolysis were studied in vitro using computerized thromboelastography and native whole blood. WEB 2086 (3.0, 30, 150, and 300 microM) had no apparent effect on the split point (SP), reaction time (R) and lysis of the clot. The biKoatugulierung time (K) was prolonged, the angle (alpha) and maximum amplitude (MA) were diminished, and the overall coagulation index (TEG index) was smaller. SP and R indicate onset of coagulation with the formation of fibrin strands, suggesting that WEB 2086 had no effect on the plasma factors. Since the Lysis parameter reflects fibrinolysis, WEB 2086 had no demonstrable fibrinolytic activity. K, alpha and MA involve platelet function and the integrity of fibrin; the fact that these factors were affected to the exclusion of SP and R suggests an effect largely on platelets. There was lack of a dose-response relationship at this concentration range (3.0-300 microM), probably due to saturation of PAF receptors even at the lowest effective concentration. These findings are consistent with the known effects of WEB 2086 on platelet function and suggest that thromboelastography may be a useful tool in the study of the activity of PAF receptor antagonists on coagulation profiles. Furthermore, since WEB 2086 is a highly specific PAF receptor antagonist devoid of intrinsic activity, and the samples used were not treated with exogenous PAF, these results suggest that endogenous PAF may play a significant role in the normal clotting mechanism.

Azepines↗
PubMed1995

Effects L-NG-nitro arginine methyl ester (L-NAME), L-NG-monomethyl arginine (L-NMMA) and L-arginine on the antinociceptive effects of morphine in mice.

The effects of L-NG-nitro arginine methyl ester (L-NAME), L-NG-monomethyl arginine (L-NMMA), L-arginine and D-NG-nitro arginine methyl ester (D-NAME) on morphine antinociception were studied in the mouse using two nociceptive assays, the abdominal constriction and tail flick tests. In the abdominal constriction test, L-arginine and D-NAME (20 mg/kg) had no effect on the number of abdominal constrictions, nor did they affect the responses due to morphine (1 mg/kg). L-NAME and L-NMMA (10 mg/kg) exhibited marked antinociception when administered on their own, and morphine antinociception was enhanced in mice pretreated with these two agents. In the tail flick test, similar doses of L-NAME, L-NMMA, L-arginine and D-NAME had no effect on their own. D-NAME had no effect on morphine analgesia, L-NAME and L-NMMA enhanced morphine antinociception, and L-arginine attenuated morphine antinociception. Therefore, increasing the levels of NO attenuates morphine antinociception, while lowering the levels enhances it. These results suggest that NO may play an important role in pain perception, and probably in the antinociceptive responses to morphine.

Animals↗
PubMed1994

Lattice location of trace elements within minerals and at their surfaces with X-ray standing waves.

The x-ray standing waves generated by dynamical Bragg diffraction were used to directly measure lattice locations of trace elements within and at the surface of a mineral single crystal. These high-precision measurements were made on natural Iceland spar calcite cleaved along the (1014) plane and reacted with a dilute aqueous lead solution. Within the bulk crystal, naturally occurring trace manganese was found within (1014) planes, consistent with its substitution for calcium. At the crystal surface, sorbed lead was found to be highly ordered and mostly within (1014) planes. This demonstrates a powerful application of synchrotron radiation in the earth and environmental sciences.

Calcium↗
PubMed1994

Molecular dynamics simulation of a leucine zipper motif predicted for the integrase of human immunodeficiency virus type 1.

We have used the molecular dynamics (MD) simulation package AMBER4 to search the conformation of a peptide predicted as a leucine zipper motif for the human immunodeficiency virus type 1 integrase protein (HIV IN-LZM). The peptide is composed of 22 amino acid residues and its location is from Val 151 to Leu 172. The searching procedure also includes two known alpha-helices that served as positive controls--namely, a 22-residue GCN4-p1 (LZM) and a 20-residue poly (L-alanine) (PLA). A 21-residue peptide extracted from a cytochrome C crystal (CCC-t) with determined conformation as a beta-turn is also included as a negative control. At the beginning of the search, two starting conformations--namely, the standard right-handed alpha-helix and the fully stretched conformations--are generated for each peptide. Structures generated as standard alpha-helix are equilibrated at room temperature for 90 ps while structures generated as a fully stretched one are equilibrated at 600 K for 120 ps. The CCC-t and PLA helices are nearly destroyed from the beginning of equilibration. However, for both the HIV IN-LZM and the GCN4-p1 LZM structures, there is substantial helicity being retained throughout the entire course of equilibration. Although helix propagation profiles calculated indicate that both peptides possess about the same propensity to form an alpha-helix, the HIV IN-LZM helix appears to be more stable than the GCN4-p1 one as judged by a variety of analyses on both structures generated during the equilibration course. The fact that predicted HIV IN-LZM can exist as an alpha-helix is also supported by the results of high temperature equilibration run on the fully stretched structures generated. In this run, the RMS deviations between the backbone atoms of the structures with the lowest potential energy (PE) identified within every 2 ps and the structure with the lowest PE searched in the same course of simulation are calculated. For both the HIV IN-LZM and the GCN4-p1 LZM, these rms values decrease with the decrease of PE, which indicates that both structures are closer in conformations as their PEs are moved deeper into the PE well.

Amino Acid Sequence↗
PubMed1994

Action of Calloselasma rhodostoma (Malayan pit viper) venom on human blood coagulation and fibrinolysis using computerized thromboelastography (CTEG).

The effects of Malayan pit viper (Calloselasma rhodostoma) venom on human blood coagulation and fibrinolysis were studied in vitro using computerized thromboelastography. At low concentrations the venom had a coagulant effect shown by faster onset of the coagulation process (shortened SP and R), faster progress of the clot (increased angle and shortened K), and increased coagulation (TEG) index. The maximum amplitude (MA) was not affected, suggesting that the venom had no apparent effect on platelet function; and clot lysis was similar to that in the controls, suggesting that there was no primary fibrinolytic activity. At higher concentrations the venom had anticoagulant effects, SP and R were progressively shortened, but there was poor/no progress in the clot formed, evident from prolonged or absent K, diminished MA and reduced angle. These results show that C. rhodostoma venom has both coagulant and anticoagulant actions. The coagulant action may be due to Factor X activator predominance at low concentrations, while the anticoagulant action could be due to ancrod action. TEG is able to demonstrate the dual effect of this venom, previously described as a paradox, and may be a useful tool in the diagnosis and monitoring of envenomation patients.

Anticoagulants↗
PubMed1994

The genetic basis of malignant hyperthermia.

Malignant hyperthermia (MH) susceptibility remains the commonest cause of death owing to general anaesthesia. In humans, genetically predisposed to MH, anaesthesia can induce skeletal muscle rigidity, hypermetabolism and hyperthermia, which if not immediately reversed can lead to tissue injury and death. In swine, the corresponding condition leads to stress-induced deaths and devalued meat products. Aberrant behaviour in the calcium (Ca2+) release channel (the ryanodine receptor) of skeletal muscle sarcoplasmic reticulum has been implicated in the cause of both the porcine and human syndromes by biochemical, physiological and molecular genetic analysis. In swine, a single mutation in the ryanodine receptor gene (RYR1) can account for all cases of MH in all breeds, but a series of different RYR1 mutation are uncovered in human families with MH. In addition, the lack of linkage between MH and RYR1 in some families indicates a heterogeneous genetic basis for the human MH.

Animals↗