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Biomedical subjects

C Chen

Publications and source records attributed to C Chen.

At least 1,063 records · Page 59Linked to original sources
PubMed1992

Some Enzymes and Properties of the Reductive Carboxylic Acid Cycle Are Present in the Green Alga Chlamydomonas reinhardtii F-60.

The reductive carboxylic acid cycle, the autotrophic pathway of CO(2) assimilation in prokaryotes (photosynthetic and nonphotosynthetic autotrophic bacteria), was investigated in Chlamydomonas reinhardtii F-60, an algal mutant lacking a complete photosynthetic carbon reduction pathway (C(3)) due to a deficiency in phosphoribulokinase. Evidence was obtained consistent with the presence of the reductive carboxylic acid cycle in F-60. This conclusion is based on the fact that: (a) acetate approximately doubled CO(2) fixation in whole cells (4 micromoles per milligram chlorophyll per hour) and in chloroplasts (32 nanomoles per milligram chlorophyll per hour); and (b) pyruvate synthase, alpha-ketoglutarate synthase, and ATP-citrate lyase, three indicators of the cycle, were found in cell-free extracts.

Journal Article↗
PubMed1992

Early and late phase events following bioprosthetic tricuspid valve replacement.

From 1961 through 1987, 9,247 patients underwent an intracardiac repair for valvular heart disease. Five hundred thirty patients had a procedure that included a tricuspid valve operation (6%), with tricuspid valve replacement performed in 175 patients (2%), of whom 154 had a bioprosthetic valve implanted (1.7%). These 154 patients with a bioprosthetic valve in the tricuspid position are the subject of this review. There were 27 males and 127 females. Ages ranged from 10 to 75 years. There was tricuspid valve insufficiency in 139 patients (90%), and stenosis plus insufficiency in 15 (10%). Carpentier-Edwards prostheses were implanted in 83 (54%), Ionescu-Shiley in 55 (35%), Hancock in 12 (8%), and Mitroflow in 4 (3%). Concomitant procedures were performed in 146 patients (95%). At least one previous operation had been performed in 86 patients (56%). Preoperatively, 139 patients were in functional Class III or IV (90%). Hospital death occurred in 20 patients (13%). Logistic regression analysis revealed that incremental risk factors for hospital death included increasing peripheral edema preoperatively (p = 0.04), and use of a Hancock prosthesis in the tricuspid position (p = 0.03). All 134 hospital survivors were followed at a mean of 66.01 months, range 1 to 162 months. There were 70 late deaths (52%). Log-rank test indicated that incremental risk factors for late death were: longer cross-clamp time at repair (p = 0.0007); higher pulmonary artery systolic pressure preoperatively (p = 0.01); earlier date of surgery (p = 0.03); and larger tricuspid prosthesis size (p = 0.06).(ABSTRACT TRUNCATED AT 250 WORDS)

Actuarial Analysis↗
PubMed1992

Role of endothelium-derived nitric oxide in the renal hemodynamic response to amino acid infusion.

The present study was performed in anesthetized rats to compare the renal hemodynamic responses to mixed amino acids (M-AA) with those to L-arginine (L-Arg) and to examine the effect of endothelium-derived nitric oxide (EDNO) synthesis blockade on the M-AA-induced rise in renal plasma flow (RPF) and glomerular filtration rate (GFR). Intravenous infusion of both M-AA (Ser, Gly, Ala, and Pro, 0.71 mmol.100 g-1.min-1) and L-Arg (0.71 mmol.100 g-1.min-1) increased RPF and GFR. Peak increases in RPF for M-AA and L-Arg were 39.7% (P less than 0.05) and 63.4% (P less than 0.01), whereas GFR increases were 33.6% (P less than 0.05) and 46.7% (P less than 0.01, respectively). Outer cortical blood flow (OCBF) was increased with both treatments. Sodium excretion and urine flow were increased more with L-Arg than M-AA (both P less than 0.01). Infusion of the nitric oxide synthesis inhibitor, nitro-L-arginine (N-L-Arg, 20 micrograms.100 g-1.min-1) increased mean arterial pressure but decreased RPF 48.4% (P less than 0.001), OCBF 39.5% (P less than 0.001), GFR 37.8% (P less than 0.01), urine flow 29.8% (P less than 0.01), and sodium excretion 40.9% (P less than 0.01). When M-AA was administered after N-L-Arg, significant increases in OCBF, RPF, and GFR were observed (P less than 0.01); there was also an enhancement of sodium excretion and urine flow (both P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acids↗
PubMed1992

Direct demonstration of engraftment of human peripheral blood leukocytes in SCID mice.

One of the major problems using man-mouse chimeras is still the difficulty to demonstrate unequivocally engraftment of human cells in murine tissues. Using supravital labelling of human leukocytes with the Hoechst dye H33342, it was possible to demonstrate directly their engraftment and to assess their distribution in the tissues of the severe combined immunodeficiency (SCID) mice. The human cells can be traced for a period of 4-5 weeks. In contrast to earlier reports, combined marker and labelled-cell studies suggest that T-cell surface marker CD3 with reported specificity for human lymphocytes are indeed found, also in man-mouse chimeras, only on human cells. The ratio of B and T cells of human origin changes significantly after transfer into SCID mice and differs among various SCID tissues. The simple staining procedure using the supravital nuclear dye H33342 opens new possibilities for the study of cellular interactions and host responses of the human immunoreactive cells in an increasingly well-characterized animal model.

Animals↗
PubMed1992

Noninvasive measurement of the time constant of left ventricular relaxation using the continuous-wave Doppler velocity profile of mitral regurgitation.

BACKGROUND: The time constant of isovolumic relaxation (tau) is an important parameter of ventricular diastolic function, but the need for invasive measurement with high-fidelity catheters has limited its use in general clinical cardiology. The Doppler mitral regurgitant velocity spectrum can be used to estimate left ventricular (LV) pressure throughout systole and may provide a new noninvasive method for estimating tau. METHODS AND RESULTS: Mitral regurgitation was produced in nine dogs, and ventricular relaxation was adjusted pharmacologically and with hypothermia. High-fidelity ventricular pressures were recorded, and tau was calculated from these hemodynamic data (tau H) assuming a zero-pressure asymptote. Continuous-wave mitral regurgitant velocity profiles were obtained, and the ventriculo-atrial (VA) pressure gradient was calculated by the simplified Bernoulli equation; tau was calculated from the Doppler data from the time of maximal negative dP/dt until LV-LA pressure crossover. Three methods were used to correct the Doppler VA gradient to better approximate the LV pressure before calculating tau: 1) adding actual LA V wave pressure (to yield tau LA); 2) adding 10 mm Hg (tau 10); and 3) no adjustment at all (actual VA gradient used to calculate tau 0). The agreement between tau H and the three Doppler estimates of tau was assessed by linear regression and by the mean and standard deviation of the error between the measurements (delta tau). the measurements (delta tau). tau H ranged from 29 to 135 msec. Without correction for LA pressure, the Doppler estimate of tau seriously underestimated tau H: tau 0 = 0.30 tau H + 9.4, r = 0.79, delta tau = -35 +/- 18 msec. This error was almost completely eliminated by adding actual LA pressure to the VA pressure gradient: tau LA = 0.92 tau H + 7.6, r = 0.95, delta tau = 2 +/- 7 msec. Addition of a fixed LA pressure estimate of 10 mm Hg to the VA gradient yielded an estimate that was almost as good: tau 10 = 0.89 tau H + 4.9, r = 0.88, delta tau = -2 +/- 12 msec. In general, tau was overestimated when actual LA pressure was below this assumed value, and vice versa. Numerical analysis demonstrated that assuming LA pressure to be 10 mm Hg should yield estimates of tau accurate to +/- 15% between true LA pressures of 5 and 20 mm Hg. CONCLUSIONS: This study demonstrates that the Doppler mitral regurgitant velocity profile can be used to provide a direct and noninvasive measurement of tau. Because mitral regurgitation is very common in cardiac patients, this method may allow more routine assessment of tau in clinical and research settings, leading to a better understanding of the role of impaired ventricular relaxation in diastolic dysfunction and the effect of therapeutic interventions.

Animals↗
PubMed1992

Liposome-mediated transfection of intact viral particles reveals that plasma membrane penetration determines permissivity of tissue culture cells to rotavirus.

Rotaviruses are an important cause of gastroenteritis in human infants. In vivo, rotavirus displays striking cell tropism with viral replication generally restricted to the villus tip enterocytes of the small intestine. We studied a panel of cell lines that vary significantly in their permissivity to rotavirus infection. L cells and HEp2 cells were relatively resistant to rotavirus infection compared with permissive Ma104 cells and HT29 cells. RNA transcription among the cell lines was proportional to antigen synthesis making a translational or posttranslational block an unlikely source of observed differences in susceptibility. All of the cell lines bound and internalized radiolabeled virus equally well, as measured by escape from surface protease treatment. Analysis of the escape of cell bound virus from neutralizing monoclonal antibody revealed that rotavirus did not immediately enter an eclipse phase in nonpermissive cells, but was internalized in an infectious form for several hours, possibly sequestered within endocytic vacuoles. L cells and HEp2 cells were as permissive as Ma104 and HT29 cells when rotavirus infection was mediated by transfection of single- or double-shelled rotavirus particles with cationic liposomes (Lipofectin). Rotavirus cell tropism in tissue culture cells is determined by the ability of infecting virions to traverse the plasma membrane of the cells into the cytoplasmic compartment.

Animals↗
PubMed1992

[Age-dependent changes in the adenylate cyclase system of rat ventral prostate].

Changes in beta-adrenoceptors, GTP binding (G) proteins and adenylate cyclase (AC) activity of ventral prostates of rats during aging were studied in these experiments. The density of beta-adrenoceptors increased markedly after birth, reaching a maximum in the tissues at 16 weeks of age and remained at this level for about 90 weeks. When stimulated by isoproterenol, the AC activity increased 4- and 22-fold in 2- and 8-week-old rats, respectively, but only 7-fold in both 16- and 104-week-old rats. Activation of AC by forskolin was the greatest during the 2 weeks after birth and then showed a sharp decrease, reaching a plateau in the tissues at 8 weeks. Bmax value of [35S]GTP gamma S binding to the tissues was the largest at 8 weeks. Pretreatment of the tissues with pertussis or cholera toxin caused age-dependent changes in both the binding abilities of Gi and Gs proteins to GTP that coincided with changes in the binding of G proteins to GTP. There was no difference between the abilities of Gi and Gs proteins to bind to GTP in the tissues of rats of the respective age. These results show that changes in the binding ability of G proteins to GTP influence the function of ventral prostates of rats during the aging process, and this is mediated through the regulation of AC activity.

Adenylyl Cyclases↗
PubMed1992

Effect of adenosine triphosphate on the postischemic left ventricular function of the immature myocardium.

In this study, the effect of exogenous adenosine triphosphate (ATP) on the immature myocardium was evaluated. Isolated working neonatal rabbit hearts were perfused aerobically for 15 min with Krebs-Henseleit buffer (KHB) at 37 degrees C, and then arrested with St. Thomas solution (STS) in group 1 and STS containing 500 mumol/L of ATP in group 2 at 4 degrees to 6 degrees C and maintained at 10 degrees to 14 degrees C for 60 min. Hearts were reperfused with KHB aerobically at 37 degrees C for 15 min. Each heart served as its own control before and after arrest. Systolic function was significantly depressed in group 1 compared with group 2. There was a significant decrease in the peak left ventricular (LV) systolic pressure in group 1 (preischemia mean [PIM] 54 mm Hg to postischemia mean [PoIM] 42 mm Hg, Student's t test p = 0.007) than in group 2 (PIM 66 to PoIM 62 mm Hg, p = 0.5). The LV pulse pressure decreased in group 1 (PIM 72 to PoIM 54 mm Hg, p = 0.02) but not in group 2 (PIM 84 to PoIM 86 mm Hg, p = 0.9) and the rate of rise of LV pressure (dP/dT) in group 2 improved (PIM 5718 to PoIM 6926 mm Hg, p = 0.4) compared with group 1 (PIM 7021 to PoIM 4125 mm Hg, p = 0.008). The PoIM LV flow (LVF) was greater in group 2 than group 1 (LVF group 1 = 2.7 ml/min, group 2 = 4.5 ml/min). Diastolic pressures were not significantly different in the two groups. Our findings suggest that the incorporation of ATP in STS has a significant effect in improving postischemic LV systolic function in neonatal rabbit hearts.

Adenosine Triphosphate↗
PubMed1992

Recovery of glucose-induced insulin secretion in a rat model of NIDDM is not accompanied by return of the B-cell GLUT2 glucose transporter.

The NSTZ rat model combines loss of glucose-induced insulin secretion with a reduced amount of the high Km B-cell glucose transporter, GLUT2. The purpose of this study was to determine whether the restoration of glucose-induced insulin secretion was paralleled by an increase of GLUT2. Rats injected at 2 days of age with 90 mg/kg STZ were studied at 8-13 wk of age. Insulin secretion was assessed in the isolated perfused pancreas with 16.7 mM glucose preceded by 40 min of 0 or 5.5 mM glucose. In control rats, 16.7 mM glucose caused the same large biphasic insulin response whether preceded by 0 or 5.5 mM glucose. In NSTZ rats, after 5.5 mM glucose, 16.7 mM glucose elicited virtually no rise in insulin release. In contrast, after 0 mM glucose, a large insulin response to the glucose challenge occurred that was equal to that of the control groups when the differences in B-cell mass were taken into account. However, the dose-response curve for glucose-induced insulin secretion was shifted to the left, and no second phase of insulin secretion was observed. GLUT2 was assessed after the perfusions by indirect immunofluorescence with anti-GLUT2 antisera. Both control groups showed homogenous staining in all B-cells. NSTZ rats perfused with 5.5 mM glucose had a marked diminution in GLUT2 staining. We observed no increase in GLUT2 staining in the NSTZ rats perfused with 0 mM glucose.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

[Histological study of tissues surrounding an overloaded mandibular apatite implant and its antagonist teeth at three months].

UNLABELLED: The objective of this study is to compare the degree of the occlusal-bearing ability of 2-piece apatite implant to that of natural dentition. It is conducted by placing implants at M2 and M2 areas of adult monkey. Four months later, the occlusal vertical dimension was raised to apply the occlusal force only on the implants by inserting connected crowns on M3M2M1 and M1M2M3. Three months after loading, the tissues surrounding the implants and the antagonist teeth were histologically examined. RESULTS: The antagonist teeth: The connected antagonist teeth show much bone resorption on the inner surface of the alveolar wall and the roots are partly in direct contact with the bone and intruded. Implant: 1. Due to the resorption from extraction, enhanced remodeling is seen in the compact bone of the experimental site. The degree of remodeling is higher toward the coronal direction. 2. Realigned functionally oblique toward the implant, thickened trabeculae, of both the lamellae and woven bone, supported the implant. 3. Bone formed widely on the buccal and lingual surfaces of the compact bone near the implant. In the areas of close to the direct contact of the implant to the compact bone, remodeling with osteon realignment in the axial direction was observed. 4. Most embedded surfaces of the implant were covered and bound to the bone.

Animals↗
PubMed1992

Clinical evaluation of a new saturation/hematocrit monitor.

The purpose of this study was to evaluate the utility of the Cobe SAT/HCT Monitor, an in-line device which continuously displays hematocrit and venous oxygen saturation. A fiber optic cable was used to connect the monitor to a "window" on the blood inlet of a venous reservoir (Cobe CML). Sixty venous blood samples were drawn from 20 patients undergoing cardiopulmonary bypass. Statistical correlations were performed comparing monitor readings with controls measured by an IL 482 co-oximeter and a TRIAC centrifuge. Results showed a high degree of correlation between the monitor and control values for both venous saturation (r = .96) and for hematocrit (r = .94). Although this device has some minor deficiencies, it is a useful tool which enables the perfusionist to monitor two important components of oxygen consumption.

Adult↗
PubMed1992

[Active life expectancy in Taiwan: compression or expansion?].

"This paper applies the multiple-decrement life table to the analysis of mortality and self-reported disability [for Taiwan], annually from 1986 until 1989.... It was found that during this period of time, the shifts in 'mortality' and 'disability' curves conform to the compression hypothesis. The area in between the two curves [has] shrunk in the 4 year period.... The sex differential in disability has been examined. It is concluded that though at the younger ages women tend to spend less person-years in disability, the situation is quite different at older ages. Women tend to have greater chance [of] and longer duration suffering from disability at old age than men." (SUMMARY IN ENG)

Adult↗
PubMed1992

[Associations between plasma insulin and high blood pressure].

We studied the relationship between plasma insulin level and hypertension in 510 cases with normal glucose tolerance and impaired glucose tolerance. In nonobese group (BMI < 25kg/m2), plasma insulin was higher in those with hypertension than those with normal blood pressure (P < 0.0001). There was no correlation between diastole blood pressure and plasma insulin; multiple regression analysis showed that fasting plasma insulin was significantly associated with systolic blood pressure after controlling age, BMI and plasma glucose level (beta = 0.27, P = 0.0078). The result suggested that age, BMI and plasma insulin level were independent risk factors of hypertension. In obese group (BMI > 25kg/m2), blood pressure was significantly associated with age and BMI, there was no association between blood pressure and plasma insulin level.

Adult↗
PubMed1992

A double-blind, randomised, cross-over study comparing the 50g OGTT and the 75g OGTT for pregnant women in the third trimester.

There is little consensus in the conduct and interpretation of the oral glucose tolerance test (OGTT) in pregnancy. In Singapore much data has been accumulated about the 50g OGTT while the converse is true of the 75g OGTT. A double-blind, randomised, crossover study of 56 subjects in the third trimester was conducted to compare both glucose challenges to determine if there was a difference in glucose handling in the context of a two hour OGTT. A significant difference (p < 0.001, t = 5.76) was found at two hours where the mean glucose concentrations were 5.2 +/- 0.8 mmol/L and 6.2 +/- 1.4 mmol/L for the 50g and 75g OGTT respectively. These findings suggest that the 75g OGTT is potentially more effective in unmasking pregnant subjects with impaired glucose tolerance.

Adolescent↗
PubMed1992

Myositis ossificans progressiva mimicking ankylosing spondylitis: a case report.

Myositis ossificans progressiva is a rare disorder of young adults characterized by ossification of the connective tissue of the voluntary muscles and ligaments. Although it is trauma-related, up to 40-60% of these patients have no history of previous injury. A young female with marked kyphosis and ankylosis of the spine presented with a recent onset of a rapidly growing painful mass over the anterior aspect of her left shoulder. She received an excisional biopsy but recurrent ossification developed soon after. It then spread to the biceps muscle with subsequent contracture deformities of the shoulder and elbow joints. A plain radiogram of her spine revealed similar characteristics of ankylosing spondylitis. However, the final diagnosis was made by the pathognomonic ectopic ossification of muscles and para-articular soft tissue. Despite poor response of the established constracture, the painful mass did respond well to prednisolone treatment within 2 months, in terms of size and consistency.

Adult↗