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Biomedical subjects

G J Schmidt

Publications and source records attributed to G J Schmidt.

At least 19 recordsLinked to original sources
PubMed2000

Phylogeny and biogeography of Eupatorium (Asteraceae: Eupatorieae) based on nuclear ITS sequence data.

The classification of the predominantly Neotropical Eupatorieae depends upon the circumscription of the core genus Eupatorium. The recently proposed narrowing of Eupatorium to ∼42 species in eastern temperate North America, Europe, and eastern Asia was tested with phylogenetic analysis of nucleotide sequence variation in the internal transcribed spacer (ITS) region of nuclear ribosomal DNA. A total of 40 samples (36 species) of Eupatorieae was analyzed. Several species from North America, South America, and Eurasia that were formerly recognized within a large Eupatorium s.l. (sensu lato) were included in the study. Other taxa included were representative of the majority of the subtribes native to eastern temperate North America. Parsimony analysis supported the contention that Eupatorium be defined narrowly and suggested that Eupatoriadelphus is distinct. The tree topology suggested that Eupatorium and Eupatoriadelphus share a common North American ancestor with Liatris relative to other Eupatorieae. It was apparent that the presumed sister taxa in Eupatoriinae from South America belong to a different clade. These results suggest that, following initial divergence in North America, Eupatorium reached Europe via dispersal during the late Pliocene with subsequent radiation in Asia.

Journal Article↗
PubMed1998

The Singapore Youth Coronary Risk and Physical Activity Study.

The purpose of this study was to examine coronary risk factors and physical activity patterns of primary and secondary school children in Singapore. Children 6-18 yr (730 boys, 849 girls) were evaluated for anthropometry, percent body fat, resting blood pressure, fasting plasma lipids and lipoproteins and glucose. A physical activity and leisure pursuits self-reported survey was used to group children into five categories ranging from "inactive" to "vigorous" activity. The self-reported questionnaire also recorded individual responses to exercise behaviors, leisure activities, and participation in organized games and sports. Body weight, body mass index (BMI; kg x m[-2]), and percent body fat were compared by age and gender. The blood analysis showed no significant differences in boys' and girls' plasma lipid and lipoprotein concentrations. Physical activity was significantly correlated with total cholesterol (rs = -0.13, P = 0.018) and triglycerides (rs = -0.18, P = 0.001) for boys and between physical activity with body fat (rs = -0.22, P = 0.0001) and BMI (rs = -0.16, P = 0.01) for girls. Height, weight, BMI, percent body fat, and blood pressure were greater for each age to 14 yr, after which there was less recorded body fat for boys. Girls' body fat remained about the same after 14 yr. Comparing by gender and age, significant differences were found between physical activity groups and total cholesterol and body fat. Although few children were at risk for heart disease, this study provides baseline coronary risk and physical activity data for further longitudinal analysis in this population.

Adolescent↗
PubMed1997

Blood pressure, lipids, lipoproteins, body fat and physical activity of Singapore children.

OBJECTIVE: To determine body composition, coronary risk factors and physical activity and the inter-relationships of these variables in Singaporean school children. METHODOLOGY: This study examined 1681 children (784 boys and 897 girls) from eight primary and seven secondary schools to determine percentiles for body stature and composition, blood pressure, lipids/lipoproteins and blood glucose by gender for three age divisions. An exercise and leisure pursuit questionnaire was administered to ascertain self-reported physical activity patterns. Anthropometric data and blood pressure readings were taken. Capillary blood was drawn from each child via finger prick sampling following an overnight fast. The concentrations of total cholesterol (TCHOL), triglyceride (TG), high-density lipoprotein cholesterol (HDL-C) and glucose (GLU) were determined from plasma using a dry chemistry analyser. Low-density lipoprotein cholesterol (LDL-C), very low-density lipoprotein cholesterol (VLDL) and the TCHOL/HDL-C ratio were determined by calculation. RESULTS: While 47.7% of boys and 22.0% of girls disclosed active lifestyles, differences between the active and non-active children were found in coronary risk factors TCHOL, LDL-C, TG, TCHOL/HDL-C and per cent body fat. No differences were shown between the two groups in HDL-C, GLU and blood pressure. There was a high correlation between the various measures of body composition with the highest correlation (r = 0.806, P < 0.001) found between body mass index (BMI) and waist measurements. CONCLUSIONS: Children in this study who reported no activity or relatively little activity were found to have TCHOL, LDL-C, TG, TCHOL/HDL-C and per cent body fat that were higher than those who reported moderately high or vigorous physical activity patterns.

Adipose Tissue↗
PubMed1995

Muscular endurance and flexibility components of the Singapore National Physical Fitness Award.

The selection of fitness tests for national fitness test batteries has been a major concern over the last decade in many countries. The present study examined muscular endurance and flexibility components of the Singapore National Physical Fitness Award (NAPFA) Scheme and compared the results with other similar fitness test protocols. A total of 286 subjects (149 males, 137 females) voluntarily participated and were divided into six age and gender groups. Significant correlations and no statistical differences (p < .05) were found between abdominal endurance using different protocols indicating that any of the alternative tests could be substituted for the NAPFA sit up test which has been classified as a contraindicated exercise (MacFarlane, 1993). In upper body muscular endurance tests, secondary age boys and all adults showed a high correlation (p < .01) with alternative test protocols. Replacement of the pull up test with the Vermont modified pull up test was recommended for primary and secondary boys because of the low number and many zero scores from the present NAPFA test. From this study it was concluded that the sit-and-reach test measured using a zero reference point from the floor could replace the present sit-and-reach test because the alternative protocol accounted for arm and leg differences. These findings provide safer and relevant alternative protocols for a national battery of field fitness assessments.

Abdominal Muscles↗
PubMed1988

Preretinal oxygen changes in the rabbit under conditions of light and dark.

Preretinal oxygen measurements were made in pigmented rabbits under conditions of light and dark. The avascular rabbit retina was chosen to eliminate the effects of autoregulation by the retinal vasculature, thus more clearly defining the role of the photoreceptors on preretinal measurements of oxygen delivery from the choroid. Measurements were made 50-100 micron away from the retina using oxygen microelectrodes. An average preretinal oxygen value of 9.8 +/- 1.3 SE mm Hg (n = 12) was measured in room light under normoxic conditions. A change from light to dark conditions always resulted in a measured decrease in preretinal oxygen levels. During the first 30 min of dark adaptation, a 25.8% (+/- 5.5% SD) decrease was obtained. This oxygen decrease is reversible during sequential light adaptation, reaching plateau in approximately 15-20 min. These results indicate that the photoreceptors have a significant effect on choroidal oxygen transmission across the retina.

Animals↗
PubMed1987

A-protein catalyzes the ADP-ribosylation of G-protein from cow rod outer segments.

A 20-kilodalton adenosine nucleotide-binding protein (A-protein) extracted from rod outer segments is shown to catalyze the cholera toxin-mediated ADP-ribosylation of GTP-binding protein (G-protein) from the outer segment. Radiolabel from [adenylate-32P] NAD+ was associated specifically with both the alpha-subunit of G-protein and with A-protein in the presence of activated cholera toxin. In the absence of added A-protein, G-protein appears to undergo ADP-ribosylation at a slower rate. In the absence of G-protein, A-protein was found to be labeled following incubation with [adenylate-32P]NAD+ and cholera toxin. In the presence of G-protein, a light-dependent component of A-protein labeling was observed. A-protein is a labile component of rod outer segments and has an affinity for ADP. The findings suggest that A-protein may act as an ADP-ribosyltransferase in the cholera toxin-mediated ADP-ribosylation of G-protein.

ADP Ribose Transferases↗
PubMed1987

The intraocular environment and experimental anaerobic bacterial endophthalmitis.

Anaerobic bacteria are prevalent in conjunctival flora but have not been adequately investigated as possible causes of endophthalmitis. The mean oxidation-reduction potential (Eh) of the rabbit vitreous was found to be +25.1 mV, well within the limiting Eh value of many anaerobes. There was an oxygen pressure gradient in the vitreous ranging from 2.1 mm Hg immediately posterior to the lens to approximately 20 mm Hg adjacent to the medullary ray. Endophthalmitis was produced with pure cultures of Fusobacterium necrophorum, Propionibacterium acnes, and Peptostreptococcus magnus. Relatively small inoculates of F necrophorum caused severe, acute endophthalmitis with scleral perforation; P acnes and P magnus produced a self-limited endophthalmitis; and vitreoretinal fibrosis was a sequela of the Propionibacterium acnes infection.

Animals↗
PubMed1986

Endonuclease banding of isolated mammalian metaphase chromosomes.

Evidence is presented that endonuclease digestion of isolated, unfixed chromosomes results in the production of banding patterns similar to those produced by digestion of fixed, air-dried chromosomes. Mouse L cell chromosomes were isolated under acidic or relatively neutral pH conditions, exposed in situ (as wet mounts on glass slides) or in vitro (in suspension) to micrococcal nuclease, Alu I or Eco RI, treated with a buffered salt solution, and stained with Giemsa. After any of these endonuclease treatments in situ, the centromeric regions of the chromosomes were intensely stained, characteristic of the C-banding observed in fixed chromosomes exposed to the same treatments. Although the fixed chromosomes were morphologically well-preserved after endonuclease digestion, the morphology of chromosomes digested in situ was variable, ranging from normal to swollen to highly distorted chromosomes. In the latter, the endonucleases induced dispersion of non-C-band chromatin; however, C-bands were still apparent as condensed, differentially-stained regions. Exposure of isolated chromosomes to Alu I in vitro also resulted in well-defined C-banding and led to the extraction of about 70% of the chromosomal DNA. From these results, the mechanism of endonuclease-induced C-banding appears to involve the dispersion and extraction of digested chromatin.

Animals↗
PubMed1982

Rhodopsin-to-metarhodopsin II transition triggers amplified changes in cytosol ATP and ADP in intact retinal rod outer segments.

We have observed rapid, light-initiated changes in unbound cytosol ATP and ADP during the rhodopsin-to-metarhodopsin II transition in intact rod outer segments (ROS). Upon illumination of the ROS, ATP is rapidly removed from the unbound phase of ROS, accompanied by the concomitant release of ADP into the cytosol. The exchange process involves decreases of approximately equal to 0.5 mM ATP in ROS cytosol ATP content in response to a saturating flash. At levels of light well below saturation (less than 0.001% bleach), the process is highly amplified, with a decrease in cytosol ATP of approximately equal to 2,000 ATP molecules per absorbed photon per ROS. Rapid time-resolution techniques reveal that cytosol ATP content decreases rapidly, within 250 msec of a saturating flash. Bleaching rhodopsin to metarhodopsin II results in a decrease in cytosol ATP, accompanied by an increase in cytosol ADP, whereas photoreversal of metarhodopsin II by a blue flash reverses the process, increasing ATP concentration to its control level in the dark. The photoreversibility of the ATP decrease during the rhodopsin-to-metarhodopsin II transition establishes a direct link between the state of an early intermediate of photolyzed rhodopsin and the state of a nucleoside triphosphate in intact ROS. The results are consistent with a light-activated exchange of unbound ATP for bound ADP, and we propose, therefore, an ATP/ADP amplification cycle in which metarhodopsin II catalyzes the exchange of ATP for ADP on a nucleotide binding protein.

Adenosine Diphosphate↗
PubMed1980

Determination of urinary placental estriol by reversed-phase liquid chromatography with fluorescence detection.

Ww describe a liquid-chromatographic procedure for determining urinary estriol concentrations. The urine sample, after enzymatic hydrolysis to free the conjugated estrogen, is extracted with ether, and an aliquot of the resulting extraction residue is injected into the liquid chromatograph. Sample components are separated with a reversed-phase C18 column and isocratic elution with an acetonitrile/water mobile phase. Using a far-ultraviolet excitation wavelength, we measure the natural fluorescence of the eluted estrogen with a fluorescence detector. The procedure provides excellent sensitivity for determing near-term pregnancy concentrations of urinary estriol. The selectivity of the method limits the effect of potentially interfering compounds.

Chromatography, Gas↗
PubMed1979

Determination of phenylalanine in serum using reversed-phase liquid chromatography and fluorescence detection.

A liquid chromatography procedure is reported for determining phenylalanine in small volumes of serum. A 10-microliter volume of serum was deproteinized with ethanol and an aliquot was derivatized with dansyl chloride reagent. The dansylated phenylalanine and the norleucine internal standard were separated using reversed-phase chromatography and measured with a fluorescence detector. Linearity was excellent over the range 50-800 mg/l. Within-run precision was better than 4%. Total analysis time including chromatography was approximately 40 min. As little as 300 pg of dansylated phenylalanine was detected.

Chromatography, Liquid↗
PubMed1978

Determination of polyamines by liquid chromatography and precolumn labelling for fluorescence detection.

Procedures are described for the separation and detection of picomole quantities of putrescine, spermidine, and spermine by liquid chromatography. The polyamines are labelled by precolumn derivatization with dansyl chloride followed by reversed-phase chromatography with a methanol and water mobile phase. The derivatized polyamines are measured with a fluorescence detector using an excitation wavelength of 340 nm and emission wavelength of 515 nm. The polyamines are eluted within 12 min and 0.5 ng of each could be detected. Some preliminary data on urine samples is presented.

Chromatography, Liquid↗
PubMed1978

A micro liquid column chromatography procedure for twelve anticonvulsants and some of their metabolites.

Solvent extracts of 50 microliter volumes of serum were sufficient for the determination of twelve anticonvulsant drugs. The liquid chromatography procedure utilized a C-18 reversed-phase column and isocratic elution with 15% acetonitrile in water. No derivatization was required. Eluted anticonvulsants were detected by UV absorption at 195 nm and quantitated by drug--internal standard peak area ratios. The procedure provided linear working curves over the concentration range from 1 to 100 mg/l of drug in the serum. The procedure for serum provided recoveries of the drugs from 92 to 101%. Within-day precision was about 4% and day-to-day precision was about 6.5%. The procedures has been applied to urine samples to facilitate bioavailability studies. Data are also given for several metabolites. There is a discussion of many practical aspects of the procedure to improve the reliability of the results.

Anticonvulsants↗
PubMed1978

Estrogen determination using liquid chromatography with precolumn fluorescence labeling.

A liquid chromatography procedure is described for the determination of some estrogens using fluorescence detection. The estrogens are labeled by precolumn derivatization with 5-dimethylaminonaphthalene-1-sulfonylchloride (dansyl chloride) and chromatographed on a reversed-phase, C-18 column with a mobile phase consisting of methanol, water, and acetic acid. The eluted analytes are measured with a fluorescence detector using excitation and emission wavelengths of 350 and 540 nm, respectively. The chief advantage of this new procedure is its sensitivity, requiring smaller amounts of sample to detect and quantitate estrogens in biological materials. We could detect less than 400 pg of estriol. With our procedure, this corresponded to about 25 ng in the final reaction mixture, before derivatization. The use of smaller sample volumes could improve this limit. Linearity for dansylated estriol, estrone, and estradiol was excellent over the estrogen range below 100 micrograms in the sample. This corresponds to approximately 1.7 micrograms on the column. Within-run precision was better than 5% for the full extraction and derivatization procedure for estriol from pregnancy urine samples. Chromatography is complete within 10 min for dansylated estriol, estrone, and estradiol.

Chromatography, Liquid↗
PubMed1978

Hemoglobins Aida (alpha 64 Asp leads to Asn) and D-Los Angeles (beta 121 Glu leads to Gln) in an Asian-Indian family.

Hemoglobins D-Los Angeles (beta 121 Gln) and Aida (alpha 64 Asn) were encountered in an Asian Indian, unassociated with any clinical manifestations. These hemoglobins had normal oxygen affinities and were stable to heat and isopropanol. The ratio of alpha chain synthesis to beta chain synthesis was close to unity. The identical change in isoelectric points of the two variants produced an interesting electrophoretic pattern.

Amino Acids↗
PubMed1978

Liquid-chromatographic procedure for tricyclic drugs and their metabolites in plasma.

We describe a procedure for determining amitriptyline and imipramine and their active metabolites nortriptyline and desipramine, respectively, at therapeutic concentrations in human plasma by use of liquid chromatography. The drugs are extracted at pH 10.5 into hexane/isoamyl alcohol, which is evaporated and the residue chromatographed. Protriptyline is used as the internal standard. As little as 10 microgram of each drug per liter could be detected in plasma, the limit being established by variability in drug-free plasmas. The day-to-day coefficient of variation for each drug at a concentration of about 100 microgram/liter was about 7%. Doxepin and diphenhydramine interfere with the analysis of amitriptyline. Total analysis time for a single sample is 20 min.

Amitriptyline↗
PubMed1977

Ultramicro GC determination of amino acids using glass open tubular columns and a nitrogen-selective detector.

A glass open tubular (capillary) column together with a nitrogen-selective detector were evaluated for the analysis of amino acids by gas chromatography. Test samples included normal and abnormal human sera and urine and several hydrolysates of pure proteins. Amino acids in the biological samples were isolated by ion exchange pretreatment and derivatized to the n-propyl, N-acetyl derivatives. Protein hydrolysates were derivatized without pretreatment. Compared with a flame ionization detector, the nitrogen-selective detector gave a sensitivity enhancement of 80x-180x for the amino acid derivatives, depending on the particular amino acid. Long-term stability of the detector was excellent. Reproducibility studies gave a long-term precision of about 6% for serum or urine samples while a precision of 5% was obtainable on a day-to-day basis when analyzing protein hydrolyzates. The experiments showed that amino acids at the picomole level could be reliably analyzed with the system. The open tubular column coated with a mixture of Carbowax 20M and Silar 5 CP and having a very thin liquid phase film gave greatly improved thermal stability compared with a previously used packed column.

Amino Acids↗