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Biomedical subjects

J C Smith

Publications and source records attributed to J C Smith.

At least 199 records · Page 11Linked to original sources
PubMed1996

Relaxation: mapping an uncharted world.

Nine hundred and forty practitioners of massage, abbreviated progressive muscle relaxation (PMR), yoga stretching, breathing, imagery meditation, and various combination treatments described their technique experiences on an 82-item wordlist. Factor analysis yielded 10 interpretable relaxation categories: Joyful Affects and Appraisals (Joyful), Distant, Calm, Aware, Prayerful, Accepted, Untroubled, Limp, Silent, and Mystery The relaxation response and cognitive/somatic specificity models predict Calm and Limp, which account for only 5.5% of the variance of relaxation experience. Unlike much of previous relaxation research, we found important technique differences. PMR and massage are associated with Distant and Limp; yoga stretching, breathing, and meditation with Aware; meditation with Prayerful and all techniques except PMR with Joyful. Results are consistent with cognitive-behavioral relaxation theory and have implications for relaxation theory, treatment, training, assessment, and research. We close with a revised model of relaxation that posits three global dimensions; tension-relief, passive disengagement, and passive engagement.

Adult↗
PubMed1996

Calcium, magnesium, and phosphorus content of hair from two populations of rhesus monkeys.

The use of hair for the assessment of human mineral nutritional status is controversial, yet has potential because of the ease of collection and storage, and the high concentration of minerals in hair. This study generated baseline values for hair macromineral content in the most commonly used primate model for human nutrition and disease, the rhesus monkey. Hair digests from monkeys in Maryland (n = 98) and Puerto Rico (n = 208) were analyzed by inductively coupled plasma atomic emission spectrometry (ICP-AES). Significant differences existed between the two populations for hair calcium (Ca), magnesium (Mg), and phosphorus (P) (P < 0.01, P < 0.001, P < 0.02). Male hair had higher concentrations of Mg in specimens from the Puerto Rican population (P < 0.001), whereas hair phosphorus was higher in female hair (P < 0.02). There were no significant differences attributable to pregnancy status. Differences in hair content attributable to categorical age were found for Ca and Mg (P < 0.001, P < 0.01). Significant location differences paralleled dietary differences. These values therefore can be considered reference ranges for hair Ca, Mg, and P for free-ranging and caged rhesus monkeys.

Age Factors↗
PubMed1996

Copper, iron, manganese, and zinc content of hair from two populations of rhesus monkeys.

The concentrations of the elements copper (Cu), iron (Fe), manganese (Mn), and zinc (Zn) in hair of caged (in Maryland) and free-ranging (in Puerto Rico) rhesus monkey populations were determined. Significant chronological age-related decreases were evident for the trace elements Mn and Zn in both populations (P < or = 0.01) and for Cu and Fe in free-ranging monkeys (P < or = 0.005). The only overall gender difference was higher hair Mn concentration in free-ranging males than in females (P < 0.03). There were no significant differences in hair Cu, Fe, or Mn related to pregnancy status. Hair Zn was lower in samples from pregnant than from nonpregnant monkeys from the caged monkeys (P < or = 0.05), but did not differ in the free-ranging monkeys. Comparison of the two populations revealed that hair Zn levels were significantly higher in caged vs free-ranging animals (P < 0.001). We attribute this higher hair Zn in the caged monkeys to contact and ingestion of Zn from their galvanized enclosures. Hair iron levels were significantly higher (P < 0.001) in free-ranging monkeys, possibly as a result of Fe-rich soil ingestion from their environment. These data support continued investigation of the use of hair as an indicator of the exposure of large groups or populations to potentially high levels of specific minerals, and the use of nonhuman primates as models for the study of trace element deficiency and/or toxicity in humans.

Age Factors↗
PubMed1996

Uptake of drugs by catheters: the influence of the drug molecule on sorption by polyurethane catheters.

The sorption of drugs by indwelling intravenous catheters may have clinical consequences both by alteration of the dose received by the patient and by physically affecting the catheter materials themselves which may lead to changes in mechanical properties and biocompatibility. Studies of drug sorption to new catheter materials are therefore important. Pellethane, a polyurethane increasingly used in vascular access catheters, is as yet little studied in terms of its capacity for drug sorption. In this work a range of drugs known to be sorbed by PVC infusion sets were studied with respect to their sorption by Pellethane catheters. Standard lengths of catheter were incubated with solutions of drugs and samples of the solution were taken at intervals, assayed spectrophotometrically and compared with control solutions incubated without catheter. Losses from solution of up to 93% were found after 24 h. A series of highly sorbing and clinically relevant drugs was identified and their uptake was studied until equilibrium had been reached. A correlation was evident between the octanol/water partition coefficient and the fraction of drug taken up from solution at equilibrium, with the more hydrophobic drugs being taken up to a greater extent by the catheter.

Adsorption↗
PubMed1996

Thermodynamic stability of water molecules in the bacteriorhodopsin proton channel: a molecular dynamics free energy perturbation study.

The proton transfer activity of the light-driven proton pump, bacteriorhodopsin (bR) in the photochemical cycle might imply internal water molecules. The free energy of inserting water molecules in specific sites along the bR transmembrane channel has been calculated using molecular dynamics simulations based on a microscopic model. The existence of internal hydration is related to the free energy change on transfer of a water molecule from bulk solvent into a specific binding site. Thermodynamic integration and perturbation methods were used to calculate free energies of hydration for each hydrated model from molecular dynamics simulations of the creation of water molecules into specific protein-binding sites. A rigorous statistical mechanical formulation allowing the calculation of the free energy of transfer of water molecules from the bulk to a protein cavity is used to estimate the probabilities of occupancy in the putative bR proton channel. The channel contains a region lined primarily by nonpolar side-chains. Nevertheless, the results indicate that the transfer of four water molecules from bulk water to this apparently hydrophobic region is thermodynamically permitted. The column forms a continuous hydrogen-bonded chain over 12 A between a proton donor, Asp 96, and the retinal Schiff base acceptor. The presence of two water molecules in direct hydrogen-bonding association with the Schiff base is found to be strongly favorable thermodynamically. The implications of these results for the mechanism of proton transfer in bR are discussed.

Amino Acid Sequence↗
PubMed1996

The Oxford Laser Prostate Trial: a double-blind randomized controlled trial of contact vaporization of the prostate against transurethral resection; preliminary results.

OBJECTIVE: To compare the results of contact laser vaporization and transurethral resection of the prostate (TURP) in a double-blind randomized controlled clinical trial. PATIENTS AND METHODS: The study comprised 148 patients with clinical benign prostatic hypertrophy (BPH) who were recruited and allocated randomly to undergo either TURP (72 patients) or laser ablation of the prostate (76 patients). The outcome was assessed using the American Urological Association (AUA -7) symptom score after 1 and 3 months as the primary measure and by urinary flow rates, haematological factors and the duration of hospital stay and length of catheterization. RESULTS: With 90% statistical power, the results at 3 months showed no clinical or statistical difference between the treatments in change in AUA symptom score. A lower blood loss, hospital stay and duration of catheterization significantly favoured the laser treatment, although the failure rate of trial without catheter and the rate of re-operation were higher after laser treatment. CONCLUSIONS: These early data are encouraging for this technique, although the outcome after one year requires evaluation before advocating the widespread uptake of this method.

Aged↗
PubMed1996

Comparison of methods of assessing vitamin A status in children.

OBJECTIVE: A study of children (2-8 years; n = 613) in Belize, Central America, was conducted to determine what proportion of the children might be at risk of vitamin A (vit A) deficiency. The data provide an opportunity to compare results of three methods of assessing vit A status in a population which was not severely malnourished. Serum retinyl ester concentrations were also determined; their relevance to one of the tests, the relative dose response (RDR) test, is discussed. METHODS: The three methods of assessing vit A status were: RDR test, fasting serum retinol concentration, and conjunctival impression cytology (CIC). Retinol-binding protein (RBP), serum retinyl esters and serum zinc concentrations were also determined. RESULTS: Inadequate vit A status was indicated for 17% of subjects by the RDR test (14% cutoff), for 24% by fasting serum retinol concentration (< 0.87 mumol/L), and for 49% by "abnormal" CIC score. Retinyl esters constituted 24% of serum retinoids at the time (5 hours after a retinyl palmitate dose) at which the second blood sample is taken for the RDR test. Regression tree analyses (CART) indicated ethnicity was a predictor of RDR score; ethnicity, stunting and age were predictors of fasting serum retinol concentration; ethnicity and stunting were predictors of 0-hour retinyl ester concentration. CONCLUSION: The three indices of vit A status did not identify the same individuals nor indicate the same percentage of the population to be at risk for vit A deficiency. Increased concentrations of retinyl esters at 5 hours compared to those at 0 hours suggest that insufficient retinol may have been taken up by the liver at 5 hours to release all accumulated retinol-binding protein (RBP) in deficient individuals; prevalence of vit A deficiency might therefore be underestimated by the RDR test. The selection of ethnicity as a predictor of RDR score and of 0-hour retinol and retinyl ester concentrations suggests that factors other than vit A status affect vit A metabolism and may affect the RDR test.

Belize↗
PubMed1996

Reproducibility of relative dose response (RDR) test and serum retinol and retinyl ester concentrations in children after a 2-week interval.

OBJECTIVE: Reproducibility of the relative dose response test (RDR), a test designed to measure vitamin A status, was tested in 23 Belizean children, 5-8 years after 2-week interval during which no treatment was given. METHODS: As required for the RDR test, serum retinol concentrations were determined before and 5 hours after an oral dose of vitamin A. An RDR score > 14% was used as the criterion of inadequate vitamin A status. The HPLC method used to measure serum retinol concentrations also determined the concentrations of four retinyl esters. RESULTS: The RDR test was reproducible for 17 of 23 subjects: 3 scored > 14% on both tests; 14, < 14% on both. Six subjects scored > 14% on only one test. The concordance correlation coefficient (rc) for the percent change in the two tests was 0.24; for fasting serum retinol concentration, rc = 0.81. For retinyl palmitate and stearate, the esters present in highest concentrations at 5 hours, concordance correlation coefficients were 0.75 and 0.59, respectively. CONCLUSION: The failure of the RDR test to classify 26% of the subjects reproducibly reduces the usefulness of the test. In addition, the reproducibility of the retinyl ester concentrations in serum 5 hours after the retinyl palmitate dose and the relatively high concentrations in some subjects suggests that some individuals may not metabolize sufficient retinol in 5 hours to cause a maximal increase in serum retinol, resulting in an underestimation of deficiency in a population in which the RDR test is used.

Anticarcinogenic Agents↗
PubMed1996

Serum carotenoid concentrations and their reproducibility in children in Belize.

Suggestions that carotenoid-containing foods are beneficial in maintaining health have led to several studies of circulating carotenoid concentrations of adults. Because few data are available for children, we report serum carotenoid concentrations of 493 children in Belize. Carotenoid concentrations were determined as part of a survey of vitamin A status of children, most between 65 and 89 mo of age. Reproducibility was tested by collecting a second blood sample 2 wk after the first collection from a subset of children (n = 23) who consumed their habitual diet with no treatment during the interim. Predominant serum carotenoids were lutein/zeaxanthin and beta-carotene, which accounted for 26% and 24% of median total carotenoids, respectively. The three provitamin A carotenoids, alpha- and beta-carotene and beta-cryptoxanthin, constituted 51% of median total carotenoid concentrations. Partial correlations of each carotenoid with fasting retinol concentration indicated that beta-carotene had the highest correlation. Concordance correlation coefficients (rc) for fasting carotenoid concentrations determined 2 wk apart were > or = 0.89 for lycopene, beta-cryptoxanthin, and alpha- and beta-carotene. The rc for lutein/zeaxanthin and total carotenoids was lower, 0.59 and 0.68, respectively, because of higher lutein/zeaxanthin concentrations at the second sampling than at the first. The reproducibility of the concentrations suggests both that individuals have characteristic profiles and that serum carotenoid concentrations can be measured randomly over > or = 2 wk without significant bias.

Belize↗
PubMed1996

The epidemiology of rotavirus diarrhea in the United States: surveillance and estimates of disease burden.

The decision to develop rotavirus vaccines was predicated on the extensive burden of rotavirus disease among children worldwide. US reports on nationwide hospitalizations (1979-1992) and deaths (1968-1991) due to diarrhea and weekly reports of rotavirus infection by 74 laboratories were reviewed to estimate the burden of rotavirus disease, identify epidemiologic trends, and consider methods for evaluating an immunization program when a vaccine becomes available. From 1968 to 1985, diarrhea-related deaths among US children <5 years old declined from 1100 to 300/year. This decline was associated with the disappearance of winter peaks for diarrhea-related deaths previously associated with rotavirus infection among children 4-23 months old. From 1979 to 1992, however, hospitalizations for diarrhea averaged 186,000/year and retained their winter peaks, which have been linked to rotavirus infections. Each year an estimated 54,000-55,000 US children are hospitalized for diarrhea, but <40 die with rotavirus. A rotavirus vaccine program will require improved surveillance, including the timely collection of data from sentinel hospitals, in which a diagnosis of rotavirus can be established or ruled out for all children hospitalized for diarrhea.

Child↗
PubMed1996

Beta-carotene and lutein protect HepG2 human liver cells against oxidant-induced damage.

Numerous epidemiological studies support a strong inverse relationship between consumption of carotenoid-rich fruits and vegetables and the incidence of some degenerative diseases. One proposed mechanism of protection by carotenoids centers on their putative antioxidant activity, although direct evidence in support of this contention is limited at the cellular level. The antioxidant potential of beta-carotene (BC) and lutein (LUT), carotenoids with or without provitamin A activity, respectively, was evaluated using the human liver cell line HepG2. Pilot studies showed that a 90-min exposure of confluent cultures to 500 mumol/L tert-butylhydroperoxide (TBHP) at 37 degrees C significantly (P < 0.05) increased lipid peroxidation and cellular leakage of lactate dehydrogenase (LDH), and decreased the uptake of 3H-alpha-aminoisobutyric acid and 3H-2-deoxyglucose. Protein synthesis, mitochondrial activity and glucose oxidation were not affected by TBHP treatment, suggesting that the plasma membrane was the primary site of TBHP-induced damage. Overnight incubation of cultures with > or = 1 mumol/L dl-alpha-tocopherol protected cells against oxidant-induced changes. In parallel studies, overnight incubation of HepG2 in medium containing micelles with either BC or LUT (final concentrations of 1.1 and 10.9 mumol/L, respectively), the cell content of the carotenoids increased from < 0.04 to 0.32 and 3.39 nmol/mg protein, respectively. Carotenoid-loaded cells were partially or completely protected against oxidant-induced changes in lipid peroxidation, LDH release and amino acid and deoxyglucose transport. These data demonstrate that BC and LUT or their metabolites protect HepG2 cells against oxidant-induced damage and that the protective effect is independent of provitamin A activity.

Aminoisobutyric Acids↗
PubMed1996

Deliberations and evaluations of approaches, endpoints and paradigms for determining zinc dietary recommendations.

The work group considered past and future Recommended Dietary Allowances (RDAs) for zinc. Past RDAs were based in large part on metabolic balance data. Balance measurements are technically difficult and it is uncertain that they reflect true requirements. Therefore other methods should be used to determine requirements and the RDA. The best approach at this time is the factorial method. In the future, data from measurements of zinc kinetics, in relation to diet and physiological functions will provide useful insights. Future RDAs should provide for at least three levels of bioavailability: low, moderate and high. Whether adjustments should be made in the RDA to account for life style factors is a matter of philosophy. The importance of the differences (gaps) between the RDA and usual intakes of zinc by persons who are apparently in good health, or between the RDA and other dietary guidelines, is an issue for consideration.

Adolescent↗
PubMed1996

Photoperiod control of the melatonin rhythm and reproductive maturation in the juvenile Djungarian hamster: 60-Hz magnetic field exposure effects.

Photoperiodic regulation of the melatonin rhythm was studied in juvenile Djungarian hamsters to test the hypothesis that magnetic field (MF) exposures disrupt sexual maturation. Juveniles in long or short days postweaning were exposed each day to a 1-gauss 60-Hz MF (15 min, 2 h before lights-off). At age 25 days, nighttime duration of the melatonin rise in the pineal gland and circulation of sham-treated controls (adjacent coil system but without current) was < 8 h in long-day juveniles and nearly 13 h in short-day hamsters. This is the first study in juveniles to demonstrate that the melatonin rhythm duration is regulated by photoperiod and that reproductive development was not disrupted by daily or acute MF exposures; puberty was initiated in long days but arrested by short days, irrespective of MF treatment. In a replicate study, MF exposures had no effect on the duration of increased melatonin. In the initial and the replicate study, amplitude differences in the nighttime pineal or serum melatonin rise possibly reflected inherent variability in repetitive melatonin rhythms. In addition, effects of daily melatonin injections to arrest puberty were not blocked by daily MF exposures. The findings support the conclusion that MF exposures fail to disrupt photoperiodic time measurement or the neuroendocrine mechanism regulating reproductive maturation in the juvenile Djungarian hamster.

Animals↗
PubMed1996

Modulation of respiratory rhythm in vitro: role of Gi/o protein-mediated mechanisms.

Slice preparations from neonatal rat medulla that generate respiratory rhythm in vitro were used to test for Gi/o protein-mediated mechanisms affecting breathing rhythm in mammals. The frequency of inspiratory motor discharge recorded from hypoglossal (XII) nerve roots decreased with bath application of gamma-aminobutyric acid (GABA) and norepinephrine, as well as agonists specific for GABAB, alpha 2-adrenergic, and mu-opioid receptors; 5-hydroxytryptamine had little effect on frequency. Microinjection of these specific agonists into the pre-Bötzinger complex, the site of respiratory rhythm generation in vitro, also decreased frequency. In contrast, substance P (SP) increased frequency when it was bath applied or microinjected into the pre-Bötzinger complex. To test for involvement of Gi/o proteins, pertussis toxin (PTX) was injected into the cerebrospinal fluid of newborn rats, and slices from these animals were tested 48 h later for block of drug effects on rhythm. In PTX-treated slices the frequency decrease due to GABAB, mu-opioid, and alpha 2-adrenergic receptor activation was attenuated (P < or = 0.05), whereas the SP receptor-mediated response was unaltered. To test for involvement of K+ conductances linked to Gi/o proteins Ba2+ (0.2 mM) was added to the bath before application of drugs. Ba2+ attenuated the decrease in frequency associated with GABAB (P < or = 0.05) and mu-opioid (0.10 < or = P < or = 0.05) receptor activation, whereas the alpha 2-adrenergic and SP responses were unaltered. We conclude that GABAB and mu-opioid, but not alpha 2-adrenergic and SP, receptor activation modulates respiratory frequency via a Gi/o protein-dependent Ba(2+)-sensitive ionic conductance mechanism on neurons within the medullary locus for rhythm generation. This mechanism may be a convergent pathway for control of respiratory frequency.

Analgesics↗
PubMed1996

Blood-lipid and lactation-stage factors affecting serum vitamin E concentrations and vitamin E cholesterol ratios in dairy cattle.

The distribution of cholesterol and vitamin E among the various lipoprotein density fractions in bovine blood was measured. The percentage of total plasma vitamin E and cholesterol in the various lipoprotein fractions was very-low-density lipoprotein, 2% and 2%, respectively; low-density lipoprotein, 17% and 22%, respectively, and high-density lipoprotein. 77% and 72%, respectively. Only 3% of plasma vitamin E was not associated with the lipoproteins. Vitamin E cholesterol ratios were not significantly different among lipoprotein fractions (P = 0.3). These results indicate that vitamin E and cholesterol are distributed in equal proportions among lipoprotein fractions. Moreover, the results suggest that variation in the proportions of lipoproteins in the different density fractions would not affect the overall vitamin E cholesterol ratio of plasma. The results further imply that the total plasma vitamin E cholesterol ratio is a valid relative estimator of the vitamin E concentration per lipoprotein particle, regardless of the density distribution of particles. Total serum vitamin E and cholesterol concentrations and their ratio were then determined in commercial diary cattle in various phases of the lactation cycle. There was a significant lactation-stage effect on the serum concentration of each analyte, as well as on their ratio. However, the magnitude of the effect was much less for the ratio than for either vitamin E or cholesterol alone. These results imply that lactation stage affects serum vitamin E concentrations by influencing both the concentration of lipoprotein particles and the concentration of vitamin E within individual particles.

Animals↗
PubMed1996

Bone morphogenetic protein-4 (BMP-4) acts during gastrula stages to cause ventralization of Xenopus embryos.

Injection of RNA encoding BMP-4 into the early Xenopus embryo suppresses formation of dorsal and anterior cell types. To understand this phenomenon, it is necessary to know the stage at which BMP-4 acts. In this paper, we present three lines of evidence showing that BMP-4 misexpression has no effect on the initial steps of mesoderm induction, either dorsal or ventral, but instead causes ventralization during gastrulation. Firstly, activation of organizer-specific genes such as goosecoid, Xnot, pintallavis and noggin occurs normally in embryos injected with BMP-4 RNA, but transcript levels are then rapidly down-regulated as gastrulation proceeds. Similarly, BMP-4 does not affect the initial activation of goosecoid by activin in animal caps, but expression then declines precipitously. Secondly, embryos made ventral by injection with BMP-4 RNA cannot be rescued by grafts of Spemann's organizer at gastrula stages. Such embryos therefore differ from those made ventral by UV-irradiation, where the defect occurs early and rescue can be effected by the organizer. Finally, the dorsalizing effects of the organizer, and of the candidate dorsalizing signal noggin, both of which exert their effects during gastrulation, can be counteracted by BMP-4. Together, these experiments demonstrate that BMP-4 can act during gastrulation both to promote ventral mesoderm differentiation and to attenuate dorsalizing signals derived from the organizer.

Animals↗