Biomedical subjects

X T Wang

Publications and source records attributed to X T Wang.

At least 37 records · Page 2Linked to original sources

PubMed2000

Fatigue quality of mammalian tendons.

When excised tendons are subjected to a prolonged load, whether constant or oscillatory, fatigue damage accumulates, leading eventually to rupture. 'Fatigue quality', assessed by the time-to-rupture under a given stress, was found to vary hugely among the tendons of a wallaby hind limb. This material property correlates with the varied stresses to which tendons from different anatomical sites are exposed in life. The correlation was demonstrated by subjecting each excised tendon to a load equal to the maximum isometric force that its muscle could have developed. The time-to-rupture was then approximately the same for each tendon, on average 4.2 h. A model is introduced in which damage is proposed as the trigger for adaptation of fatigue quality. The model aims, in particular, to explain why low-stressed tendons are not made of a 'better' material, although this clearly exists since it is used in high-stressed tendons. The principle of design to a minimum quality is viable in biology because of the availability of self-repair to balance routine damage. Clinical symptoms, to be included under the general heading of 'overuse injuries', will only arise when this balance fails.

Animals↗

PubMed2000

Cardiac L-type calcium channel alpha 1-subunit is increased by cyclic adenosine monophosphate: messenger RNA and protein expression in intact bone.

L-type calcium channels have been identified previously in both osteoblast-like osteosarcoma cell lines and primary cultures of osteoblasts using numerous techniques such as patch clamp recording, drug inhibited 45Ca2+ uptake, and Fura-2 measurements, but intact bone has not been investigated. Using reverse-transcription polymerase chain reaction (RT-PCR) we found that the three major isoforms of the alpha 1-subunit of L-type calcium channels, (alpha 1C, alpha 1D, and alpha 1S) are present in RNA extracted from ROS 17/2.8 osteosarcoma cells, rat femur, and rat skull. Sequencing of most of the alpha 1C-subunit from rat femur and ROS cells revealed that the splice variants in osteosarcoma cells and intact bone differ, but there are no unique sequence variations compared with those found in other tissues. Northern blot analysis of ROS cell RNA indicated that cyclic adenosine monophosphate (cAMP), but not 1 alpha, 25-dihydroxyvitamin D3, increased the messenger RNA (mRNA) of the alpha 1C-subunit. Western blot of ROS cell lysates revealed a band of more then 220 kDa, the amount of which increased in cells treated with cAMP. Using confocal microscopy combined with immunohistochemistry in ROS cells, intact bone, and cartilage, we found that the alpha 1C-subunit of this channel is expressed in osteoblasts and chondrocytes suggesting this channel may be a pathway for signal transduction in intact tissue, because it is in osteosarcoma cell lines and primary osteoblasts grown in tissue culture.

Animals↗

PubMed2000

[Alteration of the expression of rat cardiac Galphaq/11 and Gialpha2 proteins during endothelin-1 pre-treatment].

The present study was undertaken to explore the mechanism of G protein-mediated signal transduction pathway during endothelin-1 (ET-1) pre-treatment and ischemic preconditioning (IP). Rats were divided into four groups: ET-1, IP, ischaemia-reperfusion (IR) and control groups. ET-1 pre-treatment model was prepared by administrating 0.5 nmol/(L.kg) ET-1 into rat left ventricle, whereas IP model was prepared by ligating the left coronary artery for 5 min followed by 30 min reperfusion. All the animals were subjected to 60 min regional ischaemia and 30 min reperfusion alternately and then parameters of ventricular arrhythmia and expression of cardiac Galphaq/11 and Gialpha2 were measured. The results showed that the scores of ventricular arrhythmia decreased significantly in both ET-1 and IP treated groups as compared with IR group. In comparison with control group, Galphaq/11 increased by 77.8% (P<0.05) and 110.6% (P<0.01) in IP and ET-1 group respectively. Gialpha2 showed no significant difference in IP group, while it decreased by 31.0% (P<0.01) in ET-1 group. In conclusion, activation of G alphaq/11 may be related to the protecting mechanism of ET-1 pre-treatment and IP, whereas Gialpha2 may only play a role in ET-1 pre-treatment.

Animals↗

PubMed1999

Toxic effects of cadmium and copper on the isolated heart of dogfish shark, Squalus acanthias.

The adverse effects of heavy metal ions on the heart functions of lower vertebrates are largely unknown. In the present study, the effects of Cd2+, Cu2+, and Cu+ on the cardiac functions of the heart isolated from dogfish shark, Squalus acanthias, including the epicardial electrocardiogram, ventricular developed pressure (VDP), and heart beating rate, were studied. Cadmium (10 to 100 microM) significantly decreased VDP of the isolated shark hearts in a reversible manner. However, heart beating rate was not affected by cadmium. Cadmium also induced a transient modification of the amplitude and the form of the QRS complex. Cupric ion transiently increased VDP in a concentration-dependent manner, whereas cuprous ion (1 to 100 microM) did not markedly alter the cardiac functions of shark. Cupric or cuprous ions did not change heart beating rate and electrocardiogram at concentrations of 10 to 100 microM. Our results, for the first time, demonstrated the effects of cadmium on shark heart and indicated that the cardiac effects of copper are valence dependent. An elucidation of heavy metal effects on fish cardiac functions will help to understand the complex toxicological properties of heavy metals in different species and tissues, and will provide information for management of pollution control and marine resource protection.

Animals↗

PubMed1998

Production of melanins by ceruloplasmin.

It was shown that ceruloplasmin, apart from the known oxidative conversion of dopamine into melanin, can also produce (DHI)-melanin from 5,6-dihydroxyindole and THP-melanin from tetrahydropapaveroline. Ceruloplasmin acts as an oxidase and the kinetic parameters for these oxidative reactions are reported. Since these ceruloplasmin-catalyzed reactions occur also at pH 7.4, they could have a significant physiological impact. This ceruloplasmin-oxidasic activity is enhanced by copper ions and inhibited by chelators, such as ethylenediaminetetraacetic acid (EDTA) and desferoxamine (DEF). Some possible implication of melanin production in blood are discussed.

Ceruloplasmin↗

PubMed1997

Loss of GABA-immunoreactivity in the spinal dorsal horn of rats with peripheral nerve injury and promotion of recovery by adrenal medullary grafts.

Abnormal pain-related behaviour that accompanies peripheral nerve injury may be the result of altered spinal neuronal function. The long-term loss of inhibitory function by GABA neurons in particular may be a mechanism by which abnormal neural hyperactivity occurs, leading to exaggerated sensory processing following nerve injury. In order to assess this, changes in spinal GABA immunoreactivity at several time points following constriction nerve injury were quantified in parallel with behavioural assessments of abnormal sensory responses to noxious and innocuous stimuli. In addition, the effects of spinal adrenal medullary transplants were determined since previous findings have demonstrated alleviation of behavioural pain symptoms by such transplants. In response to unilateral sciatic nerve injury, GABAergic profiles normally found in lumbar dorsal horn laminae I-III significantly decreased. The decrease was apparent three days following ligation, particularly on the side ipsilateral to the nerve injury. By two weeks, no GABAergic profiles could be seen, with the deficit appearing in the spinal dorsal horn both ipsilateral and contralateral to the unilateral peripheral nerve injury. Marked decreases in GABA-immunoreactive profiles persisted for at least up to five weeks post-injury, with partial restoration occurring by seven weeks. However, even at seven weeks, losses in GABA-immunoreactive profiles persisted in the dorsal horn ipsilateral to peripheral nerve injury. These findings were comparable in animals receiving control striated muscle transplants. In contrast, adrenal medullary transplants markedly reduced the loss in GABA-immunoreactive profiles at all time-points examined. In addition, GABA-immunoreactive profile levels were normalized near that of intact animals by five to seven weeks following nerve injury in animals with adrenal medullary transplants. Parallel improvements in sensory responses to innocuous and noxious stimuli were also observed in these animals. The results of this study indicate that peripheral nerve injury can result in severe losses in spinal inhibitory mechanisms, possibly leading to exaggerated sensory processes in persistent pain states. In addition, adrenal medullary transplants may provide a neuroprotective function in promoting recovery and improving long-term survival of GABAergic neurons in the spinal dorsal horn which have been damaged by excitotoxic injury.

Adrenal Medulla↗

PubMed1996

Modulation of K+ channel currents by serum amineoxidase in neurons.

The influence of bovine serum amineoxidase (SAO), a circulating copper-enzyme, on neuronal K+ channels is described. Bovine SAO enhanced K+ channel currents in N1E-115 neuroblastoma cells in a time-dependent manner. Unlike ceruloplasmin (another copper-protein, shown as depolarizing factor in neurons), SAO had no effect on resting potential of neurons. However, pretreatment of cells with SAO inhibited ceruloplasmin-induced membrane depolarization. Although ceruloplasmin alone inhibited K+ channel currents, it further enhanced K+ channel currents in the presence of SAO. Therefore, SAO may be another endogenous modulator of neuronal K+ channels with effect and mechanisms different from those of ceruloplasmin.

Amine Oxidase (Copper-Containing)↗

PubMed1996

Cells expressing preproenkephalin mRNA in the rat pineal gland are not serotonin-producing pinealocytes: evidence using in situ hybridization combined with immunocytochemistry for serotonin.

1. Preproenkephalin (PPEnk) mRNA expressing cells have been identified in rat pineal gland using radioactive in situ hybridization histochemistry. 2. Approximately 7% of the cells in the pineal gland (7.5 +/- 0.86, mean +/- 95% CI) express PPEnk mRNA. These cells are distributed throughout the pineal as either scattered single cells or small groups of cells with large round or oval nuclei. 3. Using in situ hybridization combined with ABC immunocytochemistry for serotonin (5-HT) in the same pineal sections, the PPEnk mRNA labeling cells are found not to be serotonin-immunoreactive cells. These data indicate that the PPEnk mRNA is expressed in a certain discrete subpopulation of cells in the rat pineal gland and these cells are not serotonin-producing pinealocytes. 4. The physiologic role of PPEnk-derived peptides in the pineal remains unknown. It is possible that these peptides either are synthesized and secreted as hormones or act as pineal paracrine signals.

Animals↗

PubMed1996

Immobilization of prostaglandin synthetase by hydrophobic adsorption.

In this article, the immobilization of prostaglandin synthetase on n-alkyl or aryl amino-agar beads by hydrophobic adsorption is reported. The effects of different hydrophobic groups in the agar beads, pH of buffer, concentration of salts on the adsorption of prostaglandin synthetase, and the properties of immobilized prostaglandin synthetase were also studied. The results showed that 20-35 mg of microsome containing PG synthetase (protein content 8-15 mg) could be adsorbed on each gram of n-dodecylamino-agar beads after suction drying the gel in the buffer of pH 5.5 (containing 0.5 mol/L KCl), 0.1 mol/L citric-phosphate at 4 degrees C. The remaining immobilized enzyme activity was over 80%. The optimum pH of immobilized PG synthetase is 8.0, similar to that of the native enzymes. The thermostability of immobilized PG synthetase in the buffer containing 0.5 mol/L KCl was increased. Immobilized PG synthetase was used as a catalyst of synthesis of prostaglandin E1. The preservation of activity after 10 working cycles was 86.2%.

Adsorption↗

PubMed1996

Domain-specific rationality in human choices: violations of utility axioms and social contexts.

This study presents a domain-specific view of human decision rationality. It explores social and ecological domain-specific psychological mechanisms underlying choice biases and violations of utility axioms. Results from both the USA and China revealed a social group domain-specific choice pattern. The irrational preference reversal in a hypothetical life-death decision problem (a classical example of framing effects) was eliminated by providing a small group or family context in which most subjects favored a risky choice option regardless of the positive/negative framing of choice outcomes. The risk preference data also indicate that the subjective scope of small group domain is larger for Chinese subjects, suggesting that human choice mechanisms are sensitive to culturally specific features of group living. A further experiment provided evidence that perceived fairness might be one major factor regulating the choice preferences found in small group (kith-and-kin) contexts. Finally, the violation of the stochastic dominance axiom of the rational theory of choice was predicted and tested. The violations were found only when the "life-death" problem was presented in small group contexts; the strongest violation was found in a family context. These results suggest that human decisions and choices are regulated by domain-specific choice mechanisms designed to solve evolutionary recurrent and adaptively important problems.

Adult↗

PubMed1996

Experimental and theoretical quantification of the development of damage in fatigue tests of bone and antler.

This study concerns the development of damage (as measured by a reduction in elastic modulus) in two kinds of bones differing considerably in their degrees of mineralisation: laminar bone from bovine femur and osteonal bone from red deer antler. Antler bone is much tougher than 'ordinary' bone and its failure properties have been investigated in: (i) monotonic tensile tests and (ii) creep rupture experiments. Tensile fatigue is another way of examining how damage develops in bone. The development of damage in the present fatigue tests was non-linear with the cycle number, the degree of non-linearity was dependent on the level of stress and followed a clearly different course for bone and antler. Antler was a more damage-tolerant material, being able to achieve a reduction in the final modulus of elasticity, just prior to failure, three times greater than 'ordinary' bone. The evolution of damage is quantified by an empirical and a graphical method and by the use of Continuum Damage Mechanics (CDM) expressions. The CDM method shows important conditions, found in antler, but not in bone, that seen necessary for achieving stable fractures and consequently producing very tough materials.

Animals↗

PubMed1996

The accumulation of fatigue microdamage in human cortical bone of two different ages in vitro.

OBJECTIVE: To analyse the development of damage during fatigue cycling of human bone. DESIGN: Changes in compliance and the cycles to failure were monitored in cortical bone samples subjected to oscillating stress in vitro. BACKGROUND: Previous studies produced mainly the relationship between the applied stress and the final cycles to failure (sigma-N(f)plots). However, cyclic stressing increases the compliance of the bone continuously, and causes a progressive mechanical/structural degradation. Recording this accumulation of damage allows one to know how close bone is to the point of failure; more importantly, it allows a more comprehensive modelling of fatigue processes in cortical bone. METHODS: The occurrence of material damage was continuously monitored during the tests. The 20 specimens came from two female subjects, 27 and 56 years old. The range of the cyclic stresses was 58-130 MPa. RESULTS: The damage was quantified with a graphical and an empirical/numerical method, and we have also microscopically observed the generation of internal microcracks. The range of cycles to failure was from 1 to 210,000. CONCLUSIONS: It was observed that (i) the older tissue showed a lower fatigue strength than the younger one, (ii) both tissues sustained similar damage levels prior to failure, and (iii) they both showed a continuous accumulation of damage during the tests, the course of which depended on the level of stress.

Journal Article↗

PubMed1995

Creep rupture of wallaby tail tendons.

The tail tendons from wallabies (Macropus rufogriseus) suffer creep rupture at stresses of 10 MPa or above, whereas their yield stress in a dynamic test is about 144 MPa. At stresses between 20 and 80 MPa, the time-to-rupture decreases exponentially with stress, but at 10 MPa, the lifetime is well above this exponential. For comparison, the stress on a wallaby tail tendon, when its muscle contracts isometrically, is about 13.5 MPa. Creep lifetime depends sharply on temperature and on specimen length, in contrast to strength and stiffness as observed in dynamic tests. The creep curve (strain versus time) can be considered as a combination of primary creep (decelerating strain) and tertiary creep (accelerating strain). Primary creep is non-damaging, but tertiary creep is accompanied by accumulating damage, with loss of stiffness and strength. 'Damage' is quantitatively defined as the fractional loss of stiffness. A creep theory is developed in which the whole of tertiary creep and, in particular, the creep lifetime are predicted from measurements made at the onset of creep, when the tendon is undamaged. This theory is based on a 'damage hypothesis', which can be stated as: damaged material no longer contributes to stiffness and strength, whereas intact material makes its full contribution to both.

Animals↗

PubMed1995

Fatigue rupture of wallaby tail tendons.

Wallaby tail tendons fail after repeated application of stresses much lower than would be needed to break them in a single pull. We show that this a fatigue phenomenon, distinct from the creep rupture that occurs after prolonged application of a constant stress. The two phenomena are disctinguished by experiments in which tensile stress is cycled at different frequencies, ranging from 1 to 50 Hz.

Animals↗

PubMed1994

Joint chromatographic purification of bovine serum ceruloplasmin and amineoxidase.

A purification procedure leading to a joint separation of two serum copper-enzymes: ceruloplasmin (EC 1.16.3.1) and amineoxidase (EC 1.4.3.6), is described. Both enzymes are obtained in electrophoretically homogeneous form and their specific activities are higher than those obtained by previously described purification techniques. Two common steps: precipitation of bovine plasma proteins with ammonium sulphate (at 35% and 55% saturation) followed by column chromatography on AE-Agarose (obtained by treatment of agarose beads with 1-chloro-2-ethylamine), lead to an electrophoretically homogeneous ceruloplasmin. At the same time, the ceruloplasmin-free protein preparation eluted in a first peak, following further Q-Sepharose and Con A-Sepharose chromatography, leads to purified bovine serum amine oxidase (BSAO) with an improved yield. The emphasis was given to a mutual improving effect as a consequence of the integration of the two enzymes purification procedures.

Amine Oxidase (Copper-Containing)↗

PubMed1993

Changes in cognitive and emotional processing with reproductive status.

Behavioral ratings on several affective scales (non-erotic/erotic, unpleasant/pleasant, simple/complex and low arousal/high arousal), and electrophysiological responses (event-related brain potentials) to emotional pictures, were collected from 30 female subjects, at different phases of their menstrual cycle. The pictures belonged to 5 emotional categories, whose content was babies, dermatological cases, ordinary people, male models and female models. The subjects were grouped into hormone defined phases, according to their expected levels of androgens, estrogen or progesterone. The data were analyzed to determine if emotional or cognitive processing was sensitive to the reproductive status, as indicated by menstrual phase. Only one component of event-related potentials, the P3 component, varied with menstrual phase. Baby and male model pictures elicited larger P3 waves when progesterone level was high. High progesterone was also associated with a decrease in complexity and eroticism to all picture categories. An increase in the pleasantness of all categories was evident when estrogen levels were high. The results are interpreted as support for a general proximal design, whereby emotional and cognitive processes are adaptively regulated by reproductive status.

Adult↗

PubMed1993

[Treatment of myelodysplastic syndrome by combined traditional Chinese medicine and Western medicine therapy].

50 cases were treated with Myelodysplastic Syndrome (MDS) by combined TCM-WM therapy. They were classified into RA 17 cases, RAS 6, RAEB 19, CMML 1 and RAEBT 7. The patients were divided into two groups, one with RA and RAS receiving treatment of hemopoietic and immune drugs plus Chinese medicinal herbs, the other with RAEB, CMML and RAEBT receiving treatment of LD Ara-c and LD Hom chemotherapy plus medicinal herbs. The effective rates were 47.83% and 62.96% respectively, the total effective rate being 56%. 6 cases (RAEB 4, RA 1, RAS 1) were treated with all-trans retinoic acid used as an inducer of differentiation, 2 of them were effective. 11 patients with MDS who had transformed into acute leukemia were treated by LD Ara-c and combined TCM-WM chemotherapy, the remission rate was 54.55% and the survival period was 9-27 months after remission. In some cases low dose chemotherapy resulted in hemocytopenia, bone marrow inhibition, infection, mild nausea and anorexia.

Adolescent↗

PubMed1991

The relationship between menstrual phase and the P3 component of ERPs.

Event-related potentials (ERPs) and behavioral ratings were collected from 30 female subjects who were exposed to picture slides. The slides belonged to five affective categories whose content was babies, dermatological cases, ordinary people, male models, and female models. Based on the day of testing relative to their menstrual cycle, the subjects were grouped according to their expected levels of androgens, estrogen, or progesterone. The data were examined to determine whether any ERP component or behavioral rating (non-erotic/erotic, unpleasant/pleasant, simple/complex, and low arousal/high arousal) varied as a function of subjects' hormone defined menstrual phase. Only the P3 component was sensitive to menstrual phase. The P3 to babies and male models was largest when progesterone levels were high. High progesterone was also associated with a decrease in the complexity and eroticism of all slide categories. An increase in the pleasantness of all categories was evident when estrogen levels were high. The results are interpreted as support for an "adaptive context updating" theory of the P3 component of ERPs.

Adult↗