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Biomedical subjects

L H Chen

Publications and source records attributed to L H Chen.

At least 145 records · Page 8Linked to original sources
PubMed1975

Effect of leaf water deficit on stomatal and nonstomatal regulation of net carbon dioxide assimilation.

The effect of leaf water deficit on net CO(2) assimilation was studied under two conditions: in one, the stomata were allowed to contribute to the regulation of CO(2) assimilation; in the other, air was forced through the leaf at a constant rate to overcome the effects of change in stomatal resistance accompanying changes in leaf water deficit. When the stomata were allowed to regulate the gaseous diffusive resistance of the leaf, CO(2) assimilation decreased with increasing leaf water deficit. However, when air was forced through the leaf, the rate of assimilation was not inhibited by increasing leaf water deficit. The results indicate that the inhibition of net CO(2) assimilation with increasing leaf water deficit is a consequence of an increase in the diffusive resistance to gas exchange and not of a change in apparent mesophyll resistance.

Journal Article↗
PubMed1975

Effects of irradiance and leaf water deficit on net carbon dioxide assimilation and mesophyll and transport resistances.

Rate of net CO(2) assimilation by soil-grown soybean plants were studied over a range of relative leaf water contents at each of four levels of irradiance. There was a large interaction between light level and leaf water deficit on the rate of CO(2) assimilation. The effect of leaf water deficit on assimilation became larger as irradiance increased. Both stomatal resistance to CO(2) transport and mesophyll resistance to CO(2) assimilation increased as leaf-water deficit increased. The increase in both resistance with changing leaf-water content was largest at high irradiance and became smaller as irradiance decreased. Relief of soil-moisture stress by watering induced large oscillations of CO(2) assimilation, stomatal resistance, and mesophyll resistance. The oscillation of the mesophyll resistance occurred in the absence of changes in relative water content and appeared to be related to oscillations in leaf temperature. The observed increase in mesophyll resistance with decreasing leaf-water content under nonoscillative conditions may be caused by changes in leaf temperature rather than leaf water content.

Journal Article↗
PubMedDate not supplied

Carrying passengers as a risk factor for crashes fatal to 16- and 17-year-old drivers.

CONTEXT: Injuries from motor vehicle crashes are the leading cause of death among teenagers. Carrying passengers has been identified as a possible risk factor for these crashes. OBJECTIVE: To determine whether the presence of passengers is associated with an increased risk of crashes fatal to 16- and 17-year-old drivers and whether the risk varies by time of day and age and sex of drivers and passengers. DESIGN AND SETTING INCIDENCE: study of data from the Fatality Analysis Reporting System and General Estimates System (1992-1997), as well as the Nationwide Personal Transportation Survey (1995). SUBJECTS: Drivers aged 16 and 17 years who drove passenger cars, vans, or pickup trucks. MAIN OUTCOME MEASURE: Driver deaths per 10 million trips by number of passengers, driver age and sex, and time of day; and driver deaths per 1000 crashes by passenger age and sex. RESULTS: Compared with drivers of the same age without passengers, the relative risk of death per 10 million trips was 1.39 (95% confidence interval [CI], 1.24-1.55) for 16-year-old drivers with 1 passenger, 1.86 (95% CI, 1.56-2.20) for those with 2 passengers, and 2.82 (95% CI, 2.27-3.50) for those with 3 or more passengers. The relative risk of death was 1.48 (95% CI, 1.35-1.62) for 17-year-old drivers with 1 passenger, 2.58 (95% CI, 2.24-2.95) for those with 2 passengers, and 3.07 (95% CI, 2.50-3.77) for those with 3 or more passengers. The risk of death increased significantly for drivers transporting passengers irrespective of the time of day or sex of the driver, although male drivers were at greater risk. Driver deaths per 1000 crashes increased for 16- and 17-year-olds transporting male passengers or passengers younger than 30 years. CONCLUSION: Our data indicate that the risk of fatal injury for a 16- or 17-year-old driver increases with the number of passengers. This result supports inclusion of restrictions on carrying passengers in graduated licensing systems for young drivers.

Accidents, Traffic↗
PubMedDate not supplied

Vitamin C status of institutionalized and non-institutionalized elderly in Central Kentucky.

A survey of 139 elderly volunteers between 60 and 90 years of age was conducted to determine their vitamin C status and to investigate possible relationships between the plasma vitamin C level, the participant's age, sex, and institutionalization status. When the participants' vitamin C levels were compared by age groups (60-70, 71-80, 81-90) and sex, no significant differences were found. Higher (P<0.01) mean total and reduced plasma vitamin C levels were found in those subjects living on their own, when compared to nursing home residents. No vitamin C deficiency levels were found in the elderly population studied, although several were considered borderline.

Journal Article↗
PubMedDate not supplied

Effects of age, dietary restriction and germ-free environment on glutathione-related enzymes in Lobund-Wistar rats.

The effects of age, dietary restriction and germ-free environment on glutathione peroxidase (GP), glutathione reductase (GR) and glutathione-S-transerases (GT) were studied in 48 Lobund-Wistar male rats obtained through the Lobund Aging Study. The treatment design was a 2 x 2 x 3 factorial design (environment x food level x age). Four rats were killed at 6, 18 and 30 months for each of the following groups of rats: conventional ad libitum (CV-A), conventional restricted (CV-R), germ-free ad libitum (GF-A) and germ-free restricted (GF-R). The dietary restriction (DR) was 30%. The activities of the three enzymes in the liver cytosolic fraction were determined. The activities of DR and GT were not affected by age, and were significantly lower in the rats raised in the GF environment than in those raised in the CV environment. DR significantly increased GR in the GF environment. The total GP activity was not affected by age but significantly increased by DR and a GF environment, suggesting that these life prolonging conditions provide greater protection against organic hydroperoxides and low concentrations of hydrogen peroxide.

Journal Article↗
PubMedDate not supplied

Effects of moderate dietary restriction and age on blood parameters and metabolic enzymes in Lobund-Wistar rats.

The effects of moderate dietary restriction (DR) on certain blood parameters and metabolic enzymes were studied in 80 male Lobund-Wistar rats at 6, 12, 18, 24 and 30 months of age. Two groups of rats were fed ad libitum (AL) or restricted (DR) to 12 g per day from weaning. Adult DR rats received 30% less diet per day when compared to adult rats in AL group. Blood glycohemoglobin levels increased significantly with age in AL rats, but not in those of the DR group. Hematocrit showed a significant decrease at 24 and 30 months in both groups. Serum glucose levels in rats were not affected by either diet or age. Five enzymes in the liver cytosolic fractions were determined. Activities of pyruvate kinase (PK) and lactate dehydrogenase (LDH) were significantly lower in the DR group than in the AL group at each age. Activities of glutamate-pyruvate transaminase (GPT), glutamate-oxaloacetate transaminase (GOT) and malate dehydrogenase (MDH) were significantly higher in the DR group than in the AL group. The results suggest that moderate DR decreased the glycolytic pathway and appears to stimulate amino acid metabolism and increase gluconeogenesis.

Journal Article↗
PubMedDate not supplied

Effects of age and dietary restriction on liver glutathione transferase activities in Lobund-Wistar rats.

Glutathione-S-transferases (GST) are a group of enzymes which detoxify electrophilic xenobiotics (including drugs, carcinogens and their metabolites), and thus may be involved in the age-related pathologic process. Effects of a 30% dietary restriction on liver GST activities toward seven substrates were studied in male Lobund-Wistar (L-W) rats at 6, 12, 18, 24 and 30 months of age. The enzyme activities in the ad libitum (AL) group toward 1-chloro-2,4-dinitrobenzene (CDNB), bromosulfophthalein (BSP), 4-nitropyridine-N-oxide (NPNO), p-nitrobenzyl chloride (NBC), trans-4-phenyl-3-buten-2-one (PBO) and styrene oxide (STOX) did not change with age, while those toward 1,2-dicholoro-4-nitrobenzene (DCNB) decreased after middle age. The enzyme activities in the dietary restricted (DR) group toward CDNB and STOX did not change with age, while those toward DCNB, BSP, NPNO, NBC and PBO decreased after middle age. The DR group had significantly higher GST activities than the AL group, especially at 18 months, when BSP, NPNO, NBC and PBO were used as the substrates. Dietary restriction did not affect GST activities toward all seven substrates at old age. These results are substrate-specific, indicating that isozyme-specific changes in GST activities occur with dietary restriction and aging. The results suggest that dietary restriction enhances liver detoxification capability associated with GSH conjugation in middle age, which may contribute to the delaying of the age-related pathologic process until a later point in life in this animal model.

Journal Article↗
PubMedDate not supplied

Liver antioxidant defenses in mice fed ethanol and the AIN-76A diet.

The effects of chronic alcohol (EtOH) ingestion on antioxidant defenses in mice fed AIN-76A liquid diets were investigated. C57Bl/6 female mice were divided into three groups and fed the AIN-76A liquid EtOH diet containing EtOH to provide 31% of total caloric intake (TCI), the same basic diet containing EtOH to provide 35% of TCI, or an isocaloric AIN-76A liquid control diet. After 3 weeks, the mice were killed and livers were excised for biochemical analysis. Liver reduced glutathione (GSH) levels, and activities of both Mn-superoxide dismutase (SOD) and Cu/Zn-SOD were significantly decreased by both levels of EtOH. Activities of catalase and glutathione transferase (GT) were significantly increased, whereas glutathione peroxidase (GP) activity was not affected by either level of EtOH. Our previous study using the Lieber-DeCarli liquid EtOH diet caused a decline of total SOD and GP activities. The results suggest that chronic EtOH administration decreases liver antioxidant defenses; however, the mice fed the AIN-76A EtOH liquid diet can maintain a higher antioxidant defense capability than those fed Lieber-DeCarli EtOH liquid diet.

Animals↗
PubMedDate not supplied

Relationships of mortality with the fine and coarse fractions of long-term ambient PM10 concentrations in nonsmokers.

In a cohort of 6338 California Seventh-day Adventists, we previously observed for males associations between long-term concentrations of particulate matter (PM) with an aerodynamic diameter less than 10 microm (PM10) and 15-year mortality due to all natural causes (ANC) and lung cancer (LC) listed as underlying causes of death and due to nonmalignant respiratory disease listed as either the underlying or a contributing (CRC) cause of death. The purpose of this analysis was to determine whether these outcomes were more strongly associated with the fine (PM2.5) or the coarse (PM2.5-10) fractions of PM10. For participants who lived near an airport (n=3769), daily PM2.5 concentrations were estimated from airport visibility, and on a monthly basis, PM2.5-10 concentrations were calculated as the differences between PM10 and PM2.5. Associations between ANC, CRC, and LC mortality (1977-1992) and mean PM10, PM2.5, and PM2.5-10 concentrations at study baseline (1973-1977) were assessed using Cox proportional hazards models. Magnitudes of the PM10 associations for the males of this subgroup were similar to those for the males in the entire cohort although not statistically significant due to the smaller numbers. In single-pollutant models, for an interquartile range (IQR) increase in PM10 (29.5 microg/m3), the rate ratios (RRs) and 95% confidence intervals (CI) were 1.15 (0.94, 1.41) for ANC, 1.48 (0.93, 2.34) for CRC, and 1.84 (0.59, 5.67) for LC. For an IQR increase in PM2.5 (24.3 microg/m3), corresponding RRs (95% CI) were 1.22 (0.95, 1.58), 1.64 (0.93, 2.90), and 2.23 (0.56, 8.94), and for an IQR increase in PM2.5-10 (9.7 microg/m3), corresponding RRs (95% CI) were 1.05 (0.92, 1.20), 1.19 (0.88, 1.62), and 1.25 (0.63, 2.49), respectively. When both PM25 and PM2.5-10 were entered into the same model, the PM2.5 estimates remained stable while those of PM2.5-10 decreased. We concluded that previously observed associations of long-term ambient PM10 concentration with mortality for males were best explained by a relationship of mortality with the fine fraction of PM10 rather than with the coarse fraction of PM10.

Adult↗
PubMedDate not supplied

Butylated hydroxyanisole increases glutathione-S-transferase activity in hepatocyte culture.

The effect of butylated hydroxyanisole (BHA) on the activity of glutathione-S-transferase (GSH-S-T) in hepatocyte culture was determined. Hepatocytes from control rats and rats injected with 3-methylcholanthrene (3-MC) were isolated and cultured. The cultures were treated with various concentrations of BHA. Treatment of hepatocytes from both control and 3-MC-injected rats with 25 microM BHA for 24 or 48 hours increased GSH-S-T activity significantly. The results suggest that BHA may have a detoxifying effect against 3-MC-induced carcinogenesis, and that hepatocyte culture may be a fast and simple system to identify compounds which may potentially protect against development of cancer through induction of GSH-S-T.

Analysis of Variance↗