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Biomedical subjects

L F Zhang

Publications and source records attributed to L F Zhang.

At least 55 records · Page 3Linked to original sources
PubMed2000

Daily head-up tilt, standing or centrifugation can prevent vasoreactivity changes in arteries of simulated weightless rats.

Artificial gravity will be considered for long-duration spaceflight missions. Recent studies have shown that continuous exposure to gravity does not appear necessary to prevent the adverse effects of weightlessness, instead intermittent exposure may suffice. Vernikos et al reported that 1 G intermittent exposures with and without walking exercise was effective in preventing physiologic deconditioning with 4-d, -6 degrees bedrest, and standing at 1 G was most effective in preventing orthostatic intolerance. Our previous work has demonstrated differential adaptational changes in structure, function, and innervation state of arterial vasculature in different body regions of rat during simulated weightlessness and further suggested that these changes might be one of the most important mechanisms accounting for postflight orthostatic intolerance. We therefore designed the present study involving a comprehensive evaluation of the effect of intermittent G exposure in preventing the differential functional changes of the arteries at the end of 3-wk head-down tail suspension in rats to answer the following questions: (1) do intermittent G exposure have counteracting effect in preventing differential functional changes in arterial vasculature with tail-suspension? (2) among the treatments used in the present study, i.e., head-up tilt (HUT), standing (STD), and centrifugation (CEN), what kind of exposure is more effective? (3) how much time in daily 1 G exposure is needed to maintain the normal (1 G) vascular responsiveness?

Adaptation, Physiological↗
PubMed2000

Heat shock protein 70 expression in myocardium is blunted with simulated weightlessness.

Exposure of cardiac cells to a mild thermal or ischaemic stress, sufficient to induce HSP expression, protects them against a subsequent exposure to a more severe ischaemic stress. Over expression of HSPs by transfection of herpes simplex virus vectors in vitro or in transgenic animal in vivo can protect primary cardiac cells from subsequent exposure to severe thermal or hypoxic stress. The increases in myocardial and liver HSP70 accumulation in response to nonexertional heat stress are attenuated with senescence, and hearts from aged animals exhibit an impaired ability to produce the protective HSP. In our previous work, peculiar changes associated with aging, like lipofuscin accumulation and collagen deposition were shown in the myocardial tissue of long-term simulated weightless rats. We therefore designed the present study to examine whether the heat-stress induced HSP70 accumulation in myocardial tissue may decline with simulated weightlessness.

Animals↗
PubMed2000

Vasoconstrictor responsiveness of hind body vascular beds is diminished in tail-suspended rats.

It is well known that the mechanisms of occurrence of orthostatic intolerance induced by exposure to microgravity deal with multiple factors including alterations of arteries. In the previous works, the diminished contractile responsiveness of abdominal aorta and hind body medium-sized conduit arteries, mesenteric artery and femoral artery, were observed in tail-suspended rats, and the data showed that the femoral artery have subjected to the greatest changes. These results suggested that the vasoreactivity of resistance vessels might be affected by the real or simulated microgravity. Since the arterioles are the main site of peripheral resistance and of its regulation. Therefore, changes in responsiveness of arteriolar network, especially in the lower/hind body region, would be of primary importance in the genesis of postflight orthostatic intolerance. The aim of the present work was to examine whether simulated weightlessness may lead to an impairment in vasoconstrictor responsiveness in hind body vascular beds.

Animals↗
PubMed2000

Cardiovascular peripheral effector mechanism in postflight orthostatic intolerance: a simulation study.

Orthostatic intolerance (OI) following exposure to microgravity or head-down bed rest is frequently observed and is thought to be multifactorial origin. Although hypovolemia is considered as the primary cause of OI, the role played by other factors, such as the lowered vasoconstrictor responsiveness (VCR) of resistance vessels, the enhanced vasoconstriction response of cerebral vessels, and the depressed myocardial contractility need to be elucidated. It is difficult to assess experimentally how each of these changes would affect orthostatic tolerance and how these factors interact with each other. An alternative approach is to conduct simulation studies by use of mathematical models of cardiovascular system (CVS) capable of simulating the CVS response to orthostatic stress. This presentation describes the construction of the model used, and presents the preliminary simulation results illustrating the effects of varying individually the level of hypovolemia, VCR of the resistance vessels in lower limbs and abdominal viscera, VCR of the brain vessels or myocardial contractility on responses to orthostatic stress. The ultimate goal of our work was to integrate the new experimental findings and to simulate the complexity to get a thorough understanding of the mechanism of postflight cardiovascular dysfunction and orthostatic intolerance.

Aerospace Medicine↗
PubMed1999

Further cross-cultural validation of the theory of mental self-government.

This study was designed to achieve two objectives. The 1st was to investigate the cross-cultural validity of the Thinking Styles Inventory (TSI; R. J. Sternberg & R. K. Wagner, 1992), which is based on the theory of mental self-government (R. J. Sternberg, 1988, 1990, 1997). The 2nd was to examine the relationships between thinking styles as assessed by the TSI and a number of student characteristics, including age, gender, college class level, work experience, and travel experience. One hundred fifty-one students from the University of Hong Kong participated in the study. Results indicated that the thinking styles evaluated by the TSI could be identified among the participants. Moreover, there were significant relationships between certain thinking styles, especially creativity-relevant styles and 3 student characteristics: age, work experience, and travel experience. Implications of these findings for teaching and learning in and outside the classroom are discussed.

Adult↗
PubMed1999

Effect of aerobic training on orthostatic tolerance, circulatory response, and heart rate dynamics.

BACKGROUND: This study was performed to investigate the effects of aerobic training on orthostatic tolerance and to quantify the post-training changes in cardiovascular response and heart rate variability (HRV). METHODS: Tolerance and circulatory responses to two types of lower body negative pressure (LBNP) were examined and compared in a group of healthy male students before and after 6 mo of aerobic training, and the results were further compared with a group of athletes (runners). Changes in HRV associated with training were analyzed by conventional and time-varying autoregressive spectral analysis, as well as by approximate entropy measurement (ApEn)--a statistic quantifying heart rate "complexity" derived from non-linear dynamics. RESULTS: After aerobic training, there was an initial transient hypotension during the supine -50 mmHg LBNP testing and a significant decrease in tolerance to upright graded LBNP in most of the student-subjects. Moreover, after training, there was a significant decrease in ApEn value of the HRV time series during both supine control and LBNP testing, and the rate of cardiac vagal withdrawal and sympathetic activation during the onset of LBNP was faster than that before training. CONCLUSIONS: The present study has provided further evidence that certain types of aerobic training may affect orthostatic tolerance and may be associated with a loss of complexity of HRV during supine resting and orthostatic stress.

Adaptation, Physiological↗
PubMed1999

[Ultrastructural changes of arterial wall from different body parts of rats during simulated weightlessness].

OBJECTIVE: To test the nature of remodeling of arteries in different body parts in adapting to local hemodynamic changes induced by tail-suspension. METHOD: Ultrastructural changes of hindlimb and cerebral arteries from 4-wk tail-suspended (SUS-4), 1-wk recovered (REC-1), and control (CON) rats were studied by transmission electron microscopy. RESULT: For the hindquarter arteries, like the femoral artery and anterior tibial artery, there were fewer smooth muscle layers, less myofilaments in the smooth muscle cell (SMC), and more intercellular substance in SUS-4 group than in CON group. After 1-wk recovery, the internal elastic lamina of the arteries thickened, the amount of myofilaments in SMC increased, the content of intercellular substance restored, and neoformative SMCs emerged under the endothelium. With respect to arteries in the neck region and the brain, like the common carotid artery and basilar artery, SMCs of contractile phenotype were converted to that of synthetic phenotype, and migration and hyperplasia of SMCs also happened. After 1-wk recovery all these alterations were somewhat restored. CONCLUSION: It provided further evidence that peripheral effector mechanism might play an important role in the genesis of postflight orthostatic intolerance.

Actin Cytoskeleton↗
PubMed1999

[Effects of simulated weightlessness on vasoreactivity of hindlimb arterial bed in rats].

OBJECTIVE: To investigate the alterations in vasoreactivity of hindlimb arterial bed after simulated weightlessness. METHOD: The tail-suspended rat model was used to simulate weightlessness, and the alterations in vasoreactivity of arterial bed were examined in vitro using isolated, constant flow perfused hindlimb of 2-wk suspended rats and control rats. RESULT: Perfusion flow-pressure relationship of hindlimb arterial bed showed no significant differences between suspended rats and control rats; but vascular responses to KCl (20-100 mM) and PE(10(-8)-10(-4) M) were decreased in hindlimb arterial bed of suspended rats as compared with that of control rats. CONCLUSION: Contractile ability of resistance vessels was diminished in simulated weightlessness rats, and a compromised ability of resistance vessels to increase peripheral resistance may play an important role in occurrence of orthostatic intolerance.

Adaptation, Physiological↗
PubMed1999

[Computer simulation of cardiovascular response to lower body negative pressure].

OBJECTIVE: To simulate the cardiovascular response to lower body negative pressure (LBNP). METHOD: A computer model was developed. It had 7 subparts: the redistribution of blood, the filling of left ventricle, left ventricle, peripheral circulation, control of heart rate, control of peripheral resistance and control of venous tone. The heart rate and venous tone were controlled by high-pressure receptor baroreflex, while the peripheral resistance was controlled by high- and low-pressure receptor baroreflexes. RESULT: With the help of the model, cardiovascular response to LBNP up to -10.64 kPa (-80 mmHg) were simulated, including the changes of systolic blood pressure, mean blood pressure, heart rate and cardiac output. The time-dependent response to a LBNP profile was also simulated. The simulation results coincided well with human experiments. CONCLUSION: The model is valid and can accurately reproduce the short-term hemodynamic response to LBNP.

Aerospace Medicine↗
PubMed1999

[Vasoconstrictor responsiveness of rat basilar artery enhanced by simulated weightlessness].

OBJECTIVE: To investigate the effects of simulated weightlessness on contractile responsiveness of the basilar artery. METHODS: Rats were subjected to tail-suspension for 4-wk to simulate the effect of weightlessness, responses of perfused isolated basilar arterial rings to various vasoactive compounds were examined. RESULTS: Maximal isometric contractile responses to KCl [ (10~100) mmol/L], arginine vasopressin [AVP, (10(-15)~10(-7) mol/L], or 5-hydroxytryptamine [5-HT, (10(-12) ~ 10(-4) mol/ L] were significantly enhanced in arterial rings isolated from 4-wk tail-suspended as compared with that from simultaneous control rats. CONCLUSION: These results indicate that medium-term simulated weightlessness may result in an enhanced contractile responsiveness in rat basilar artery, and strongly support the hypothesis of cerebrovascular syncope-initiating mechanism.

Aerospace Medicine↗
PubMed1999

[Alterations of arterial vasoconstrictor responsiveness in rats during and after tail-suspension].

Objective. To characterize the time course of alterations in vasoconstrictor properties of arteries during simulated weightlessness, and to examine whether these alterations are reversible. Method. The tail-suspended rat model was used to simulate weightlessness, and the alterations in vasoconstrictor response were examined in vitro using isolated arterial rings. Result. Compared with that of controls, contractile tension evoked by KCl and phenylephrine (PE) were lower in abdominal aortic, mesenteric and femoral arterial rings from 2 wk tail-suspended rats (P<0.05); after 4 wk tail-suspension, the responses of mesenteric and femoral arterial rings to KCl or PE were further decreased (P<0.05); but contraction responses of arterial rings from 8 wk tail-suspended rats were similar to that of 4 wk simulated microgravity rats. The reversibility of altered arterial vasoreactivity after 4 wk tail-suspension was observed for 5 wk. Vasoreactivity of abdominal aortic rings was recovered after first week of recovery, but it took five weeks that altered vasoreactivity of mesenteric and femoral artery got back to normal. Conclusion. The alterations in constrictor properties of arteries are dependent on both the duration of tail-suspension and the position of artery, the diminished vasoconstrictor properties appear to reach a new steady state after 4 wk tail-suspension, and the changes are reversible.

Animals↗
PubMed1999

[Changes in lumen diameters of vessels in arteriolar network in rat soleus muscle after simulated weightlessness].

Objective. To elucidate whether simulated weightlessness can induce changes in lumen diameters of vessels in arteriolar networks in hindlimb muscles and whether these changes are reversible. Method. Changes in lumen diameters of the vessels in the arteriolar network in soleus muscle of 4 wk tail-suspended (SUS-4), 1 wk (REC-1) and 5 wk (REC-5) recovered rats were examined and compared with that of control (CON) rats by use of the method of intra-arterial infusion of a carbon suspension. Result. The lumen diameters of the feeding arteries and arcade arterioles, and the transverse arterioles of the order of both V and II in the SUS-4 group were reduced by 31%, 29%, 28%, and 41%, respectively, as compared with that of the CON group (P<0.01). The diameters of these arterioles in REC-1 group were partially restored but remained significantly less than that of the CON group (P<0.05, or P<0.01). In REC-5 group, except for the transverse arterioles of order II, the diameters of all the other arterioles were fully recovered. Conclusion. These findings indicate that a 4 wk simulated weightlessness might induce atrophic changes in the arterioles of the hindlimb muscles. It also suggests that structural changes in arteriolar network might be an important mechanism accounting for postflight orthostatic intolerance.

Animals↗
PubMed1999

[Echocardiographic assessment of left ventricular structure and function after simulated weightlessness in rats].

Objective. To investigate whether the changes in rat after simulated weightlessness are similar to those in astronaut after flight. Methods. The effects of 4 wk tail-suspension on left ventricular structure and function in rats were examined by echocardiography. Results. After 4 wk of simulated weightlessness, the thickness of both the anterior and posterior wall in left ventricle (LV) showed a general trend of decrease, but these changes were not statistically significant; the end-systolic and end-diastolic internal dimensions (ESD and EDD respectively) of LV decreased significantly; and the end-systolic volume, end-diastolic volume and stroke volume (ESV, EDV and SV respectively) were all reduced; so did the relevant indices of them. There were no significant differences in ejection fraction (EF) and fractional shortening (FS) between the tail-suspended and control groups. The left ventricular mass (LVM) and its index (LVMI) were decreased. The peak velocities of blood flow of aorta, pulmonary artery and mitral valve didn't show any significant change after simulated weightlessness. Conclusion. Medium-term simulated weightlessness may lead to a significant decrease in left ventricular internal dimension, ventricular volume, and mass, and a trend of decrease in mean left ventricular wall thickness. These changes in rats are similar to those observed in astronauts postflight.

Animals↗
PubMed1999

[Differentiated remodeling changes of medium-sized arteries from different body parts in tail-suspended rats and their reversibility].

Objective. The aim of the present study was to test whether medium-sized arteries in different body parts are differentially directed to achieve stimulus-specific remodeling to adapt local hemodynamic changes induced by tail-suspension, and to examine whether these structural changes are reversible. Method. Morphological changes of femoral, anterior tibial, common carotid, and basilar arteries from 4 wk tail-suspended (SUS-4), 1 wk recovered (REC-1), and control (CON) rats were studied using van Gieson-Orcein staining method. Result. For the hindquarter arteries, like the femoral and anterior tibial arteries, the lumen diameter (d) and medial tissue area (A) of SUS-4 group were significantly decreased (P<0.05, P<0.01) as compared with that of CON group, and that of REC-1 group were not fully recovered though the differences were not significant. With respect to arteries in the neck region and the brain, the remodeling changes were just in an opposite direction. In SUS-4 group, the d and A of both common carotid and basilar arteries were significantly increased (P<0.05, P<0.01) as compared with that of CON, and not fully restored after 1 wk recovery. Conclusion. The structures of medium-sized arteries in different body parts remodel differentially in response to local hemodynamic changes during simulated weightlessness and these changes were reversible.

Adaptation, Physiological↗
PubMed1998

Induction of cytokine messenger RNA transcripts in mouse macrophages by Listeria monocytogenes isolated from channel catfish.

OBJECTIVE: To determine whether differences exist in induction and quantity of tumor necrosis factor alpha (TNF-alpha), interleukin (IL)1 beta, and IL-10 mRNA transcripts when mouse J774A.1 macrophages are infected with Listeria monocytogenes, including 2 isolates originating from channel catfish, the wild-type virulent (EGD) strain, and a nonhemolytic strain (ATCC 15313). SAMPLES: Listeria monocytogenes isolates from kidneys or fillets of channel catfish were used to stimulate cytokine production from mouse macrophages. The RNA from the infected macrophages was collected. PROCEDURE: Four hours after infection with L monocytogenes, total cellular RNA was extracted from the J774A.1 cells and reversed transcribed to cDNA, which was amplified, using specific primers for TNF-alpha, IL-1 beta, or IL-10. The specific amplified DNA fragments were detected on polyacrylamide gels and quantified, using a reverse transcription polymerase chain reaction (PCR)-mediated ELISA. RESULTS: The wild-type hemolytic EGD strain and the 2 hemolytic catfish isolates of L monocytogenes induced higher amounts of TNF-alpha-, IL-1 beta-, and IL-10-specific mRNA in J774A.1 cells than did the nonhemolytic strain. CONCLUSIONS: Hemolysin-associated induction of TNF-alpha, IL-1 beta, and IL-10 cytokines may be related to survival and replication of L monocytogenes in macrophages. It also suggests that the PCR-mediated ELISA procedure is a sensitive test to quantify cytokines from cell cultures.

Animals↗
PubMed1998

Characterization of Listeria monocytogenes isolated from channel catfish (Ictalurus punctatus).

OBJECTIVE: To characterize Listeria monocytogenes from tissues of channel catfish for their ability to cause hemolysis and grow intracellularly in mouse macrophages. SAMPLES: 15 isolates from processed fillets and 15 isolates from the brain, spleen, and kidneys. PROCEDURE: Serotype and hemolytic activity of L monocytogenes isolates were evaluated, using plate agglutination and CAMP tests, respectively. Invasiveness of L monocytogenes was determined by inoculating each strain or isolate on J774A.1 macrophage cells. Infected cells were incubated for 0 or 3 hours and lysed; then 100 gli of the lysate was plated onto a brain heart infusion agar plate. Colony counts for each strain or isolate were analyzed statistically. RESULTS: Of 30 isolates, 19 were serotype 1 and 11 were serotype 4. Mouse J774A.1 macrophages were inoculated with catfish isolates, a wild-type (EGD) or a nonhemolytic strain of L monocytogenes. Seventy-three percent (11/15) of isolates originating from catfish organs and 100% (15/15) of isolates originating from fillets were not significantly different from the wild-type EGD strain. The nonhemolytic L monocytogenes strain used as a negative control failed to replicate. Intracellular growth of all L monocytogenes isolates decreased after an additional 3-hour incubation period with medium containing 50 [microg/ml of gentamicin. CONCLUSIONS: Similar to the wild-type EGD strain, most channel catfish L monocytogenes isolates were hemolytic, serotype 1 or 4, and were invasive for mouse J774A.1 macrophages. CLINICAL RELEVANCE: monocytogenes growth in mouse macrophages may serve as an in vitro model for determining virulence of isolates from food products or environments.

Animals↗
PubMed1997

Localization of neuropeptide Y Y1 receptors in cerebral blood vessels.

The localization of neuropeptide Y (NPY) Y1 receptor (R) -like immunoreactivity (LI) has been studied in cerebral arteries and arterioles of the rat by immunohistochemistry using fluorescence, confocal, and electron microscopy. High levels of Y1-R-LI were observed in smooth muscle cells (SMCs) in the small arterioles of the pial arterial network, especially on the basal surface of the brain, and low levels in the major basal cerebral arteries. The levels of Y1-R-LI varied strongly between adjacent SMCs. Y1-R-LI was associated with small endocytosis vesicles, mainly on the outer surface of the SMCs, but also on their endothelial side and often laterally at the interface between two SMCs. NPY-immunoreactive (Ir) nerve fibers could not be detected in association with the Y1-R-rich small arterioles but only around arteries with low Y1-R levels. A dense network of central NPY-Ir nerve fibers in the superficial layers of the brain was lying close to the strongly Y1-R-Ir small arterioles. The results indicate that NPY has a profound effect on small arterioles of the brain acting on Y1-Rs, both on the peripheral and luminal side of the SMCs. However, the source of the endogenous ligand, NPY, remains unclear. NPY released from central neurons may play a role, in addition to blood-borne NPY.

Animals↗