Measurement of salicylic acid in human serum using stable isotope dilution and gas chromatography-mass spectrometry

A simple, highly selective, and sensitive method using stable isotope dilution and gas chromatography-mass spectrometry has been developed to quantify salicylic acid (SA) at concentrations naturally occurring in biological fluids, such as in the serum of subjects not taking aspirin. After extraction of liquid-liquid with diethyl ether and ethyl acetate and preparation of the tert-butyldimethylsilyl derivative, SA content was detected using deuterated SA as internal standard. The mean recovery of SA from serum was 85 +/- 6%. Intra- and interday precision and % relative error were <15% in all cases.With a detection limit of 0.6 ng and a quantification limit of 2 ng, the method is therefore also adequate for population studies because of the small amount of blood necessary to perform the analyses.     

Occurrence,distribution and neurochemical features of small intestinal neurons projecting to the cranial mesenteric ganglion in the pig

The small intestine of the pig has been investigated for its topographical distribution of enteric neurons projecting to the cranial mesenteric ganglion, by using Fast Blue or Fluorogold as a retrogradely transported neuronal tracer. Contrary to the situation in small laboratory animals such as rat and guinea-pig, the intestinofugally projecting neurons in the porcine small intestine were not restricted to the myenteric plexus, but were observed in greater numbers in ganglia of the outer submucous plexus. The inner submucous plexus was devoid of labelled neurons. Retrogradely labelled neurons were mostly found, either singly or in small aggregates, in ganglia located within a narrow border on either side of the mesenteric attachment. For both nerve networks, their number increased from duodenum to ileum. All the retrogradely labelled neurons exhibited a multidendritic uniaxonal appearance. Some of them displayed type-III morphology and stained for serotonin. This study indicates that, in the pig, not only the myenteric plexus but also one submucous nerve network is involved in the afferent component of intestino-sympathico-intestinal reflex pathways. The finding that some of the morphologically defined type-III neurons participate in these reflexes is in accord with the earlier proposal that type-III neurons are supposed to fulfill an interneuronal role, whether intra- or extramurally.     

A low-temperature heteronuclear NMR study of two exchanging conformations of metal-bound pyoverdin PaA from Pseudomonas aeruginosa

Under iron-deficient conditions, the Gram-negative bacterium Pseudomonas aeruginosa ATCC 15692 secretes a peptidic siderophore, pyoverdin PaA, composed of an aromatic chromophore derived from 2,3-diamino-6,7-dihydroxyquinoline and a partially cyclized octapeptide, D-Ser-L-Arg-D-Ser-L-FoOHOrn-(L-Lys-L-FoOHOrn-L-Thr-L-Thr) (FoOHOrn: delta N-formyl-delta N-hydroxyornithine), in which the C-terminal carboxyl group forms a peptidic bond with the primary amine of the L-Lys side chain. Ferric iron is chelated by the catechol group on the chromophore and the two hydroxyornithine side chains. In aqueous solution, the (1)H-NMR spectrum of pyoverdin PaA-Ga(III), in which Ga(III) is used instead of Fe(III) for spectroscopic purposes, showed clear evidence of exchange broadening, preventing further structural characterization. The use of cryo-solvents allowed measurements to be made at temperatures as low as 253 K where two distinct conformations with roughly equivalent populations could be observed. (13)C and (15)N labeling of pyoverdin PaA enabled complete assignment of both forms of pyoverdin PaA-Ga(III) at 253 and 267 K, using triple-resonance multidimensional NMR experiments commonly applied to doubly labeled proteins.     

Comparison of folate quantification in foods by high-performance liquid chromatography-fluorescence detection to that by stable isotope dilution assays using high-performance liquid chromatography-tandem mass spectrometry

A comparison study on folate quantitation was carried out between the recently developed stable isotope dilution assay using liquid chromatography-tandem mass spectrometry (LC-MS-MS) and the frequently used HPLC with fluorimetric detection (LC-FD). By applying LC-MS-MS, spinach, wheat bread, beef, and blood plasma were found to contain 159.2, 19.8, 1.2, and 5.6 microg/100 g total folates, respectively, whereas the respective quantitative data obtained by LC-FD were 95.5, 16.2, 0.7, and 6.8 microg/100 g. In all samples, LC-MS-MS revealed superior selectivity and precision and circumvented the shortcomings of conventional LC techniques, i.e., ambiguous peak assignment as well as high detection limits for 5-formyltetrahydrofolate, 10-formylfolic acid, and folic acid. The affinity chromatography columns used in this study showed excellent cleanup performance and permitted detection limits as low as 0.1, 0.5, 0.1, 0.08, and 0.1 microg/100 g for tetrahydrofolate (H(4)folate), 5-methyl-H(4)folate, 5-formyl-H(4)folate, 10-formylfolate, and pteroylglutamic acid, respectively. Thus, a 10-fold higher sensitivity compared to solid-phase anion-exchange cartridges was achieved. However, affinity chromatography columns revealed a significantly higher affinity toward the natural vitamers than to the racemic isotopomeric standards, which has to be considered when applying the latter in stable isotope dilution assays.     

Regional variation in soil carbon and δ<Superscript>13</Superscript>C in forests and pastures of northeastern Costa Rica

Recent studies suggest that the direction and magnitude of changes in soil organic carbon (soil C) pools following forest-to-pasture conversion in the tropics are dependent upon initial soil conditions and local factors (e.g. pre-conversion soil C content, soil texture, vegetation productivity, and management practices). The goal of this study was to understand how landscape-scale variation in soil-forming factors influenced the response of soil C pools to forest clearing and pasture establishment in northeastern Costa Rica. We measured soil C and its stable isotopic composition in 24 paired pasture and reference forest sites distributed over large gradients of edaphic characteristics and slope throughout a 1400 km² region. We used the large difference in stable C isotopic signatures of C3 vegetation (rain forest) versus C4 vegetation (pasture grasses) as a tracer of soil C dynamics. Soil C pools to 30 cm depth ranged from 26% lower to 23% higher in pastures compared to paired forests. The presence of non-crystalline clays and percent slope explained between 27 and 37% of the variation in the direction and magnitude of the changes in soil C storage following pasture establishment. Stable carbon isotopes (¹³C) in the top soil (0–10 cm) showed a rapid incorporation of pasture-derived C following pasture establishment, but the vegetation in these pastures never became pure C4 communities. The amount of forest-derived soil C in pasture topsoils (0–10 cm) was negatively correlated to both pasture age and the concentrations of non-crystalline iron oxides. Together these results imply that site factors such as soil mineralogy are an important control over soil C storage and turnover in this region.     

Differential field response of two Mediterranean tree species to inputs of sewage sludge at the seedling stage

Land degradation and desertification is a common feature in Mediterranean landscapes due to extensive and intensive land use and natural or man induced disturbances. The ecosystem may need external inputs to recover its composition and function as soils are often impoverished and vegetal key stone species lost. We evaluated the effects of the application of fresh and air-dried biosolids in the establishment and morphological and physiological performance of seedlings of Pinus halepensis and Quercus ilex under dry Mediterranean field conditions. Seedling survival was not affected by biosolid treatments in any of the studied species both two and ten years after planting. During the first two years, growth was enhanced by the two biosolid treatments in relation to control, although the change in the biomass allocation pattern differed between species. Rooting depth was significantly enhanced by liquid biosolid in Q. ilex and marginally reduced in P. halepensis as well as the exploration of soil. As a consequence, root-to-shoot ratio reduced significantly with dry and liquid sludge due to promoted aboveground growth while maintaining and even reducing belowground fractions. An improvement of the nutritional status, of fertilized seedlings especially of phosphorus, is the explanation for the better field performance. Vector analysis revealed an important phosphorus limitation for both species that was overcome with the application of liquid (both species) and air-dried biosolid (pine). The higher growth of pine seedlings attained in the liquid biosolid treatment was coupled with a significant decrease in foliar δ¹³C, suggesting lower water use efficiency. The significant increase in foliar δ¹⁵N in the biosolid treatments in both species suggested that a large proportion of the total nitrogen uptake came from the applied biosolids. Instead, with regard to the low biosolid application rate used in the study, treatments had an overall positive effect as a restoration tool by improving nutritional status and promoting growth of planted seedlings.     

Primitivity and convergence to stability

An exact expression for the index of primitivity g of a Leslie matrix is obtained, which applies also to time-varying matrices which share an incidence matrix. Elapsed time (not time intervals) to primitivity is shown to depend only weakly on the discretization scheme used. A lower bound for speed of convergence to the stable (fixed or time-dependent as appropriate) state is given which depends sensitively on g.     

Carbon and nitrogen isotope ratios in different compartments of a healthy and a declining Picea abies forest in the Fichtelgebirge,NE Bavaria

Summary Natural carbon and nitrogen isotope ratios were measured in different compartments (needles and twigs of different ages and crown positions, litter, understorey vegetation, roots and soils of different horizons) on 5 plots of a healthy and on 8 plots of a declining Norway spruce (Picea abies (L.) Karst.) forest in the Fichtelgebirge (NE Bavaria, Germany), which has recently been described in detail (Oren et al. 1988a; Schulze et al. 1989). The ¹³C values of needles did not differ between sites or change consistently with needle age, but did decrease from the sun-to the shade-crown. This result confirms earlier conclusions from gas exchange measurements that gaseous air pollutants did no long-lasting damage in an area where such damage was expected. Twigs (¹³C between-25.3 and-27.8) were significantly less depleted in ¹³C than needles (¹³C between-27.3 and-29.1), and ¹³C in twigs increased consistently with age. The ¹⁵N values of needles ranged between-2.5 and-4.1 and varied according to stand and age. In young needles ¹⁵N decreased with needle age, but remained constant or increased in needles that were 2 or 3 years old. Needles from the healthy site were more depleted in ¹⁵N than those from the declining site. The difference between sites was greater in old needles than in young ones. This differentiation presumably reflects an earlier onset of nitrogen reallocation in needles of the declining stand. ¹⁵N values in twigs were more negative than in needles (-3.5 to-5.2) and showed age- and stand-dependent trends that were similar to the needles. ¹⁵N values of roots and soil samples increased at both stands with soil depth from-3.5 in the organic layer to +4 in the mineral soil. The ¹⁵N values of roots from the mineral soil were different from those of twigs and needles. Roots from the shallower organic layer had values similar to twigs and needles. Thus, the bulk of the assimilated nitrogen was presumably taken up by the roots from the organic layer. The problem of separation of ammonium or nitrate use by roots from different soil horizons is discussed.     

Asymptotic properties of infinite Leslie matrices

The stable population theory is classically applicable to populations in which there is a maximum age after which individuals die. Demetrius [1972. On an infinite population matrix. Math. Biosci. 13, 133-137] extended this theory to infinite Leslie matrices, in which the longevity of individuals is potentially infinite. However, Demetrius had to assume that the survival probability per time step tends to 0 with age. We generalise here the conditions of application of the stable population theory to infinite Leslie matrix models and apply these results to two examples, including or not senescence.     

δ13C and δ15N changes after dietary shift in veliger larvae of the slipper limpet Crepidula fornicata: an experimental evidence

δ¹³C and δ¹⁵N measurements are still poorly conducted in benthic invertebrate larvae. To assess the δ¹³C and δ¹⁵N changes occurring after a dietary shift, experiments were conducted on veliger larvae of Crepidula fornicata fed with two cultured microalgae (Isochrysis galbana and Pavlova lutheri) of known isotopic composition, ¹³C-enriched and ¹⁵N-depleted compared to the initial values of the larvae. Rapid changes in larval δ¹³C and δ¹⁵N were observed after the dietary shift, with an increase in δ¹³C and a decrease in δ¹⁵N. After 19 days of feeding, isotopic equilibrium was still not reached, a period which is close to the duration of the pelagic life of the larvae. This implies that the isotopic composition measured in field-collected larvae might only partly reflect actual larval feeding but also the parental isotopic signature, especially during the early developmental stages. Isotopic measurements in marine invertebrate larvae should thus be interpreted cautiously. In planktonic food web investigations, the study of field-collected larvae of different size/developmental stage may reduce potential misinterpretations.