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Biomedical subjects

R L Smith

Publications and source records attributed to R L Smith.

At least 415 records · Page 23Linked to original sources
PubMed1985

Experimental guinea pig ocular infection by Salmonella typhimurium.

The clinical, microbiologic, and cytologic features of the guinea pig model of keratoconjunctivitis with enterobacteria, Salmonella typhimurium were elucidated. Guinea pig eyes were instilled with S. typhimurium and the eyes were studied by biomicroscopy, culture, cytology, pathology, and electron microscopy. All animals developed moderate to severe conjunctivitis that was present in 18% of the animals on day 1. It became more intense, appearing in all of the eyes on day 10 and disappeared before day 30. The cultures for S. typhimurium were almost all positive on days 1 and 2, declined steadily to 10% on day 10, and were negative after that. A coarse, epithelial punctate keratitis was present in more than 90% of the infected eyes at some time during the experiment. The keratitis had a biphasic clinical course. The first peak correlated with the maximum culture results, but during the second peak only 10% of the cultures were positive. Electron microscopy of the cornea showed the S. typhimurium at the epithelial surface within surface epithelial cells during the early phases of infection. The later phase keratitis, with negative culture results, resembles the keratitis of Reiter's syndrome.

Animals↗
PubMed1985

Interreceptor junction in the double cone of the chicken retina.

The two elements of the double cones in the chicken retina (Gallus gallus domesticus) are joined by a specialized junction located at the level of the myoid of the principal cone and the perikaryon of the accessory cone, in close proximity to the outer limiting membrane. In thin sections, the plasma membranes of the two elements of the cones are seen to approach each other closely being separated by a cleft of 3 to 11 nm; short gap junctions are interposed. A layer of fine filamentous material is constantly present on the cytoplasmic side of the plasma membranes. In replicas of freeze-fractured retinas the junction appears as a fascia composed of small polygonal gap junctions connected to one another by linear gap junctions. Solitary arrays of gap junctional particles are also present. In close proximity to the gap junctions the membrane matrix appears devoid of intramembrane particles. We conclude that the elements of the double cones are connected to one another by gap junctions with associated intermediate junction. The presence of gap junctions suggests that the two elements of the double cones are electrically coupled.

Animals↗
PubMed1984

Dynamic structure of membranes by deuterium NMR.

Progress in our understanding of the dynamic structure of membrane lipids and proteins has recently been made possible by the advent of high-field "solid-state" nuclear magnetic resonance spectroscopic studies of specifically deuterium-labeled systems. Major features of lipid and protein dynamics have been deduced.

Amino Acids↗
PubMed1984

Insulin action in denervated rat hemidiaphragms. Decreased hormonal stimulation of glycogen synthesis involves both glycogen synthase and glucose transport.

Rat hemidiaphragms were denervated in vivo and then incubated in vitro to assess the ability of insulin to stimulate glycogen synthesis. Denervation for 1 day resulted in 50% decreases in the stimulation by insulin of [U-14C]glucose incorporation into glycogen, and in both the basal and the insulin-stimulated activity ratios (activity minus glucose-6-P/activity plus glucose-6-P) of glycogen synthase; however, the stimulation of 2-deoxyglucose uptake by insulin was not affected by 1 day of denervation. The hormonal stimulation of [U-14C]glucose into glycogen was decreased by 90% after 3 days of denervation. At this time, the stimulation of 2-deoxyglucose uptake by insulin was also reduced and the synthase activity ratios remained depressed. Consistent with its reduced effect on glucose transport, the hormone did not increase glucose-6-P in the 3-day denervated muscles. Furthermore, the Ka for activation of glycogen synthase by glucose-6-P was higher in denervated muscles, and denervation abolished the effect of insulin on decreasing the Ka. The results presented demonstrate that denervation rapidly reduces the extent to which glycogen synthase can be activated by insulin, and has a later effect on decreasing the stimulation of glucose transport. These two effects act synergistically to markedly decrease the hormonal stimulation of glycogen synthesis.

Animals↗
PubMed1984

The heparin-binding site of antithrombin III. Identification of a critical tryptophan in the amino acid sequence.

Chemical modification of a single tryptophan residue in antithrombin III with dimethyl(2-hydroxy-5-nitrobenzyl)sulfonium bromide blocks heparin binding and the heparin-enhanced inhibition of thrombin without altering the heparin-independent rate of thrombin inhibition (Blackburn, M. N., and Sibley, C. C. (1980) J. Biol. Chem. 255, 824-826). The labeled protein was reduced and carboxymethylated and then cleaved with cyanogen bromide. The peptide containing the hydroxynitrobenzyl-labeled tryptophan was isolated by gel filtration and ion exchange chromatography. Amino acid analysis of the labeled peptide indicates that it corresponds to residues 21 through 89 of human antithrombin III. The site of labeling corresponds to Trp 49, which is located within the disulfide-stabilized loops near the NH2-terminal end of the antithrombin III molecule.

Amino Acid Sequence↗
PubMed1984

Nuclear magnetic resonance studies of amino acids and proteins. Deuterium nuclear magnetic resonance relaxation of deuteriomethyl-labeled amino acids in crystals and in Halobacterium halobium and Escherichia coli cell membranes.

We have obtained deuterium (2H) Fourier transform nuclear magnetic resonance (NMR) spectra of zwitterionic L-[beta-2H3]alanine, DL-[gamma-2H6]valine, DL-[beta, gamma-2H4]threonine, L-[delta-2H3]leucine, and L-[alpha, beta, gamma, gamma', delta-2H10]isoleucine in the crystalline solid state and have determined the deuteriomethyl group spin-lattice relaxation rates as a function of temperature. The results yield the Arrhenius activation energies (delta E) for methyl rotation, and through use of a suitable mathematical model, rotational correlation times, tau c. For alanine, valine, threonine, leucine, and isoleucine at 37 degrees C, tau c and delta E values are 780, 100, 40, 38, and 18 ps and 22, 14.0, 17.6, 15.5, and 8.6 kJ, respectively. For L-[beta-2H3]alanine in the zwitterionic lattice, a spin-lattice relaxation time (T1) minimum of 2.1 +/- 0.3 ms is observed (at 0 degree C), in excellent agreement with the 1.92-ms prediction of the mathematical model. Similar tau c and delta E measurements are reported for bacteriorhodopsin in the purple membrane of Halobacterium halobium R1 and for Escherichia coli cell membranes. Overall, our results demonstrate a great similarity between the dynamics in amino acid crystals and in membrane proteins. However, threonine exhibits a nonlinear Arrhenius behavior in bacteriorhodopsin, and in the valine-, leucine-, and isoleucine-labeled membrane samples at higher temperatures (approximately greater than 37 degrees C), there is evidence of an additional slow side-chain motion. The lipid phase state in E. coli does not appear to influence, on the average, the dynamics of the valine side chains. These results indicate that the sensitivity of the deuterium NMR technique is now adequate to study in moderate detail the dynamics of most types of amino acids in a membrane protein and that adequate sensitivity, in some instances, should be available for the study of individual amino acids in suitably labeled membrane proteins.

Amino Acids↗
PubMed1984

Haloperidol differentially potentiates tonic immobility, the dorsal immobility response, and catalepsy in the developing rat.

The effects of a single subcutaneous injection of haloperidol (1 or 10 mg/kg) or the vehicle solution on three kinds of behavioral inhibition were investigated in rats of 10, 15, and 20 days of age. The behaviors measured were tonic immobility, a response induced by placing an animal on its back supported by a V-shaped trough; the dorsal immobility response, which can be elicited in young rodents by grasping the skin of the dorsal surface of the neck and lifting the animal into the air; and catalepsy, a form of immobility in which animals remain in unusual postures but are capable of righting themselves, and which can be elicited by drugs which block dopamine receptors. Haloperidol (10 mg/kg) significantly potentiated the duration of tonic immobility only at 10 days of age; potentiated catalepsy at all age levels, but significantly less in the 15-day-old rats than in the 10- or 20-day-old rats; and potentiated the duration of the dorsal immobility response in the 10- and 20-day-old animals but not in the 15-day-olds. These results are discussed with respect to the development of neurotransmitter systems in the brain.

Aging↗
PubMed1984

Keratan sulfate content and articular cartilage maturation during postnatal rabbit growth.

This article describes the macromolecular changes in keratan sulfate and proteoglycan that occur in rabbit articular cartilage during postnatal development. Articular cartilage glycosaminoglycans from femoral condyles and the tibial plateaus of rabbits at 8, 12, 18, and 26 weeks and 2 years of age were extracted, fractionated, and quantified. The predominant glycosaminoglycan present in articular cartilage at 8 weeks was chondroitin sulfate. During subsequent maturation the relative proportions of keratan sulfate and chondroitin sulfate varied inversely. The greatest increase in the amount of keratan sulfate present in cartilage was observed between 12 and 26 weeks of age. Hyaluronic acid content was measurable at 12 weeks; afterward the amount remained relatively constant with age. Proteoglycans, extracted from 6-, 12-, and 22-week-old rabbit femoral and tibial cartilage in the presence of protease inhibitors, were analyzed on columns of Sepharose CL-2B. Cartilage proteoglycans decreased in hydrodynamic size between 12 and 22 weeks, corresponding to the period of maximal change in content of keratan and chondroitin sulfate.

Age Factors↗
PubMed1984

Species differences in oxidative drug metabolism: some basic considerations.

Perhaps one of the single most important developments in the past 20 years in the understanding of chemical toxicity has been the realisation of the importance of metabolic transformation in this process. It is now widely appreciated that the toxic effects of many chemicals is a function of their metabolism rather than the substance itself. Of central interest to the toxicologist therefore is an understanding of the metabolism of a toxic chemical and the significance of this in the toxic process. The metabolic process itself however can be highly variable both between and within animal species. For this reason the toxicologist may have to consider both species and strain differences in metabolism when attempting to extrapolate findings to man in the safety evaluation process. For the past twenty years, work on species differences in metabolism has been largely of a descriptive nature and the cataloguing of differences. However, developments in the last few years in the understanding of the genetic diversity of species, including man, in terms of biotransformation and the nature and substrate preferences of the various multiple forms of the drug-metabolizing enzymes now give a better insight into the nature of species differences of metabolism. Furthermore, an understanding of this problem tempers expectations in terms of what may be hoped for in the extrapolation from other species. For example, the search for a species that metabolizes like man will be seen to be ill-conceived and ill-advised. The presentation deals with some of the fundamental aspects of species and strain differences in oxidative metabolism in particular and the implications that this has for the toxicologist in the safety evaluation process.

Animals↗
PubMed1984

Metabolism of anethole. I. Pathways of metabolism in the rat and mouse.

The metabolic fate of the naturally occurring food flavouring trans-anethole has been investigated in rats and mice. A single 50-mg/kg dose of trans-[methoxy-14C]anethole was given orally to female Wistar albino rats and by ip injection to male CD-1 mice. The major routes of elimination of 14C were the urine and expired air (as 14CO2). Excretion of 14C in the faeces and as volatile compounds in the expired air was very low (total less than 2% of the dose). Urinary metabolites were separated by solvent extraction, TLC and HPLC and were characterized by MS and GC-MS directly and following methylation or trimethylsilylation, the results being compared where possible with authentic standards. Eleven 14C-containing urinary metabolites were identified in the rat and ten in the mouse. These compounds arose from side-chain oxidation, side-chain cleavage and various conjugations. The major urinary metabolites were two isomers of 1-(4'-methoxyphenyl)propane-1,2-diol, 2-hydroxy-1-methylthio-1-(4'-methoxyphenyl)propane and 4-methoxyhippuric acid, the first three all being excreted as glucuronides. In addition to these 14C-labelled metabolites, 4-hydroxypropenylbenzene, the unlabelled product of oxidative O-demethylation of trans-[14C]anethole, was excreted extensively in urine as the glucuronide.

Allylbenzene Derivatives↗
PubMed1984

Metabolism of anethole. II. Influence of dose size on the route of metabolism of trans-anethole in the rat and mouse.

The effect of dose size on the metabolism of trans-anethole was investigated in rodents over the dose range 0.05-1500 mg/kg. trans-[methoxy-14C]Anethole was administered to female Wistar rats by gavage and to male CD-1 mice by ip injection. Urine, faeces and 14CO2 in expired air were collected and their 14C content was measured. Urinary metabolites were separated as described by Sangster et al. (Fd Chem. Toxic. 1984, 22, 695) and quantitated by radioHPLC and TLC. The major route of metabolism of trans-anethole in rodents is via oxidative O-demethylation and the importance of this route was found to decrease with increasing dose from 56 and 72% of the dose at 0.05 mg/kg to 32 and 35% of the dose at 1500 mg/kg in rats and mice, respectively. Over this dose range the elimination of 14C-labelled urinary metabolites increased significantly in both species. There was a species-specific regioselectivity in the side-chain oxidation of anethole. The rat favoured the epoxidation route, resulting in the elimination in the urine of two 1-(4'-methoxyphenyl)propane-1,2-diol isomers, elimination of which together rose from 2 to 15% of the dose over the dose range studied. In contrast the mouse favoured omega-oxidation, yielding cinnamyl compounds and 4-methoxybenzoic and 4-methoxyhippuric acids, the elimination of the latter two rising from 10 to 42% of the dose over the dose range studied. The species differences in metabolism, and the significance of the effect of increasing dose on the metabolic route are discussed with reference to the guidance these results could give in the assessment of the risk to man from dietary exposure to trans-anethole and related compounds.

Allylbenzene Derivatives↗
PubMed1984

Rapid and short-term adaptation in auditory nerve responses.

The peristimulatory adaptation of auditory nerve responses in Mongolian gerbil was studied. Constant-intensity tone bursts were used as stimuli. The time decay of the firing rate following the response peak at stimulus onset was described by fitting two exponentially-decaying components and a constant term to the resulting peri-stimulus-time histograms. The slower (short-term) component had an amplitude which was proportional to the driven-steady-state rate (the portion of the constant term in excess of the spontaneous rate). The short-term time constant was on the order of 60 ms and was independent of intensity. The rapid component grew more quickly with intensity and exhibited a greater dynamic range than did the short-term and steady-state components. The time constant of the rapid component was on the order of 1-10 ms, and decreased with increasing intensity in most units. At a constant intensity above unit threshold, the rapid time constant measured at CF was larger for units with low characteristic frequency (CF) than for units with high CF. These results indicate that as intensity increases, the auditory nerve fiber responds more vigorously and with greater time resolution to the onset of tonal stimuli.

Acoustic Stimulation↗
PubMed1984

Hyperinsulinemia in rats with ventromedial hypothalamic lesions: role of hyperphagia.

The relation of hyperinsulinemia to hyperphagia was examined in rats with lesions of the ventromedial hypothalamus (VMH). Plasma insulin and glucose levels were assayed after a 4-hr fast and 17 min after the initiation of a meal (6 ml of sweetened milk in 7 min) in animals with sham lesions, VMH animals maintained at preoperative body weight by food restriction, and VMH animals fed ad lib. Both VMH groups displayed basal and postabsorptive hyperinsulinemia, compared with the sham-operated control group, but insulin levels were greatest under the ad lib feeding condition. It is suggested that VMH hyperinsulinemia is due both to a primary effect of the lesion and to hyperphagia and that marked obesity can result in the absence of basal hyperinsulinemia as a result of hyperphagia with consequent postabsorptive hyperinsulinemia.

Animals↗
PubMed1984

Genetic aspects of the polymodally distributed sulphoxidation of S-carboxymethyl-L-cysteine in man.

Interindividual variation in the sulphoxidation of S-carboxymethyl-L-cysteine (750 mg p.o.) was investigated in 200 healthy volunteers. Nearly a 100-fold difference was observed between individuals with respect to the amount of sulphoxide metabolites detected in their 0-8 h urine (0.6 to 59.1% recovery). Such a difference was shown to be reproducible over several months in 40 subjects who spanned the entire range of capacities. Cumulative plots and maximum likelihood analysis of the distribution indicated that a bimodal model was most probable. Analysis of pedigree data obtained from 12 families suggested a genetic effect with overlying environmental influences.

Adolescent↗
PubMed1984

Denitrification in san francisco bay intertidal sediments.

The acetylene block technique was employed to study denitrification in intertidal estuarine sediments. Addition of nitrate to sediment slurries stimulated denitrification. During the dry season, sediment-slurry denitrification rates displayed Michaelis-Menten kinetics, and ambient NO(3) + NO(2) concentrations (</=26 muM) were below the apparent K(m) (50 muM) for nitrate. During the rainy season, when ambient NO(3) + NO(2) concentrations were higher (37 to 89 muM), an accurate estimate of the K(m) could not be obtained. Endogenous denitrification activity was confined to the upper 3 cm of the sediment column. However, the addition of nitrate to deeper sediments demonstrated immediate N(2)O production, and potential activity existed at all depths sampled (the deepest was 15 cm). Loss of N(2)O in the presence of C(2)H(2) was sometimes observed during these short-term sediment incubations. Experiments with sediment slurries and washed cell suspensions of a marine pseudomonad confirmed that this N(2)O loss was caused by incomplete blockage of N(2)O reductase by C(2)H(2) at low nitrate concentrations. Areal estimates of denitrification (in the absence of added nitrate) ranged from 0.8 to 1.2 mumol of N(2) m h (for undisturbed sediments) to 17 to 280 mumol of N(2) m h (for shaken sediment slurries).

Journal Article↗
PubMed1984

Responses of Sorghum and Pennisetum Species to the N(2)-Fixing Bacterium Azospirillum brasilense.

Three field inoculation experiments, two in Florida and one in New Mexico, were conducted with Azospirillum brasilense Cd. Each of the Florida experiments evaluated two crop species. One species in each of the Florida experiments responded to inoculation with a significant dry matter yield increases of 11 to 24% and nitrogen yield increases of 9 to 39%. No inoculation response was noted in the New Mexico experiment. The responding species were Sorghum bicolor (L.) Moench (sorghum) and the interspecific hybrid between Pennisetum americanum (L.) K. Schum. (pearl millet) and P. purpureum Schumach. (napiergrass). Nonresponding species were pearl millet (Florida) and Sorghum sudanense (Piper) Staph. (New Mexico). Acetylene reduction activity of inoculated plots in Florida was low, showing no increase over the natural uninoculated background rates and, in one case, was negatively correlated with yield. Acetylene reduction activity was not measured in New Mexico. In Florida, A. brasilense populations were found to decline from 5 x 10 to 5 x 10 bacteria g of soil in about 3 weeks (quadratic regressions). Continued decline to less than 10 by week 5 indicated that the inoculated bacteria did not become established in the soil in high numbers. The A. brasilense population declined at about the same rate in the New Mexico experiment. The erractic inoculation responses in these experiments are similar to those observed in earlier work at the University of Florida. The lack of acetylene reduction activity response to inoculation and the rapid population decline of the inoculated bacteria suggest that N(2) fixation is not the major mechanism causing yield responses after inoculation.

Journal Article↗
PubMed1984

Effect of organic contamination upon microbial distributions and heterotrophic uptake in a Cape Cod, Mass., aquifer.

Bacterial abundance, distribution, and heterotrophic uptake in a freshwater aquifer contaminated by treated sewage were determined from analyses of groundwater and sediment-core samples. The number of free-living (unattached) bacteria in contaminated groundwater declined steadily with increasing distance from the source of sewage infiltration, from 1.94 (+/- 0.20) X 10(6) ml-1 at 0.21 km to 0.25 (+/- 0.02) X 10(6) ml-1 at 0.97 km. Bacterial abundance in groundwater sampled at 0.31 km correlated strongly with specific conductance and increased sharply from 4.0 (+/- 0.3) X 10(4) ml-1 at a depth of 6 m to 1.58 (+/- 0.12) X 10(6) ml-1 at 14 m, then declined at 20 and 31 m to 1.29 (+/- 0.12) X 10(6) and 0.96 (+/- 0.12) X 10(6) ml-1, respectively. A majority of the bacteria in contaminated and uncontaminated zones of the aquifer were bound to the surfaces of particulates, less than 60 micron in diameter. The glucose uptake rate, assayed at in situ and 5 microM concentrations, declined steadily in contaminated groundwater sampled along a transect. A preparative wet-sieving technique for use in processing core samples for bacterial enumeration is described and evaluated.

Bacteria↗