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ABSTRACTThe 18O content of CO2 is a powerful tracer of photosynthetic activity at the ecosystem and global scale. Due to oxygen exchange between CO2 and 18O-enriched leaf water and retrodiffusion of most of this CO2 back to the atmosphere, leaves effectively discriminate against 18O during photosynthesis. Discrimination against 18O (Δ18O) is expected to be lower in C4 plants because of low ci and hence low retrodiffusing CO2 flux. C4 plants also generally show lower levels of carbonic anhydrase (CA) activities than C3 plants. Low CA may limit the extent of 18O exchange and further reduce Δ18O. We investigated CO2–H2O isotopic equilibrium in plants with naturally low CA activity, including two C4 (Zea mays, Sorghum bicolor) and one C3 (Phragmites australis) species. The results confirmed experimentally the occurrence of low Δ18O in C4, as well as in some C3, plants. Variations in CA activity and in the extent of CO2–H2O isotopic equilibrium (θeq) estimated from on-line measurements of Δ18O showed large range of 0–100% isotopic equilibrium (θeq = 0–1). This was consistent with direct estimates based on assays of CA activity and measurements of CO2 concentrations and residence times in the leaves. The results demonstrate the potential usefulness of Δ18O as indicator of CA activity in vivo. Sensitivity tests indicated also that the impact of θeq < 1 (incomplete isotopic equilibrium) on 18O of atmospheric CO2 can be similar for C3 and C4 plants and in both cases it increases with natural enrichment of 18O in leaf water. [ABSTRACT FROM AUTHOR]

Concentration and isotopic composition (δ13C and δ18O) of ambient CO2 and water vapour were determined within a Quercus petraea canopy, Northumberland, UK. From continuous measurements made across a 36-h period from three heights within the forest canopy, we generated mixing lines (Keeling plots) for δa 13CO2, δa C18O16O and δa H2 18O, to derive the isotopic composition of the signal being released from forest to atmosphere. These were compared directly with measurements of different respective pools within the forest system, i.e. δ13C of organic matter input for δa 13CO2, δ18O of exchangeable water for δa C18O16O and transpired water vapour for δa H2 18O. [CO2] and δa 13CO2 showed strong coupling, where the released CO2 was, on average, 4 per mil enriched compared to the organic matter of plant material in the system, suggesting either fractionation of organic material before eventual release as soil-respired CO2, or temporal differences in ecosystem discrimination. δa C18O16O was less well coupled to [CO2], probably due to the heterogeneity and transient nature of water pools (soil, leaf and moss) within the forest. Similarly, δa H2 18O was less coupled to [H2O], again reflecting the transient nature of water transpired to the forest, seen as uncoupling during times of large changes in vapour pressure deficit. The δ18O of transpired water vapour, inferred from both mixing lines at the canopy scale and direct measurement at the leaf level, approximated that of source water, confirming that an isotopic steady state held for the forest integrated over the daily cycle. This demonstrates that isotopic coupling of CO2 and water vapour within a forest canopy will depend on absolute differences in the isotopic composition of the respective pools involved in exchange and on the stability of each of these pools with time. [ABSTRACT FROM AUTHOR]

Circulating food antibodies, intestinal permeability and HLA status were studied in twelve blood donors previously identified as being selectively IgA deficient from screening 10 000 donations by means of a latex agglutination inhibition test, and confirmed by laser nephelometry. Assessment of intestinal function also included clinical history and standard laboratory tests. The donors proved to be healthy with no evidence of autoimmune disease or allergy. Nine donors (75%) had precipitins to food antigens. None had increased intestinal permeability as measured by the cellobiose/mannitol absorption test, HLA-A, B and DR antigen distribution was normal, IgG sub-class distribution was normal with the exception of an IgG2 level slightly below normal in one donor (0.9 g/l). An unexpected finding was a return of IgA levels to normal in four donors (33%) within 6 months. [ABSTRACT FROM AUTHOR]

The contribution which (photo)respiration makes to carbon isotope discrimination (Δ13C) was examined by conducting simultaneous gas exchange measurements and isotopic analysis of carbon dioxide passing over leaves of Triticum aestivum and Phaseolus vulgaris, via manipulations of the carbon isotope composition (δ13C) of source CO2 during growth and measurement. Dark respiration only altered net Δ13C (Δobs) at tow CO2 assimilation, and was sensitive to source CO2 δ13C during measurement. Photorespiration reduced Δobs relative to Δ13C predicted from p[subi]/pa (Δi) over the full range of CO2 assimilation, to a greater degree under elevated oxygen partial pressure (pO2), indicating fractionation during photorespiration (f) in T. aestivum. For P. vulgaris, Δobs was insensitive to elevated pO2 at higher assimilation rates, suggesting that f was minimal. A model was developed to calculate gross discrimination (Δps), independent of (photo)respiration, from which estimates of f were obtained for T. aestivum (3.3‰) and P. vulgaris (0.5‰). Because photorespiratory fractionation varies interspecifically, and influences net Δ13C which is directly reflected in leaf δ13C, consideration of (photo)respiratory fractionation is necessary when interpreting δ13C of leaf material, especially under conditions where (photo)respiratory CO2 losses make a large relative contribution to total plant carbon budgets. [ABSTRACT FROM AUTHOR]

In an attempt to correlate host and parasite-related events occurring during the course of a primary Giardia infection in the mouse we have measured epithelial cell kinetics, enzymes, and intraepithelial lymphocytes at different stages of the infection. New methods were developed for the accurate measurement of parasite numbers and distribution within the gut. In jejunum a modest decrease in villus length and intraepithelial lymphocytes at week 1 preceded a pronounced disaccharidase deficiency at week 2, the time of maximum trophozoite numbers, whereas crypt lengthening and increased cell production became maximal at week 3. As trophozoite numbers fell the intraepithelial lymphocyte count and disaccharidase values rose. With the exception of the intraepithelial lymphocyte count, which followed the same pattern as in jejunum but two weeks later, the changes seen in the ileum were the opposite of those in jejunum, suggesting rapid ileal adaptation. The results indicate that the disaccharidase deficiency associated with giardiasis is likely to represent a direct effect of the parasite on the brush border rather than enterocyte immaturity, whereas the intraepithelial lymphocyte response reflects host immunity to the parasite. Profound adaptive changes occur throughout the small intestine in response to a relatively localised insult. [ABSTRACT FROM PUBLISHER]

Corticosteroid therapy is known to be hazardous in patients with occult infection but the mechanism by which the host parasite relationship is altered by steroids is not known.We have used an intestinal protozoal parasite, Giardia muris, to examine the effects of corticosteroids on the number of parasites in the intestine in the course of a primary infection. A single injection of cortisone acetate, subcutaneously, one day before oral inoculation of CBA mice with 1000 cysts of Giardia muris, resulted in significantly higher trophozoite counts in animals studied at one, two, three, four, and eight weeks post-infection, when they were compared with saline injected controls. Recrudescence of occult infection was also achieved by cortisone acetate treatment of mice which had been infected with Giardia muris eight months previously. Clinical studies are required to establish if recrudescence of occult protozoal infection is an important cause of morbidity when immunosuppressive therapy is given to patients in areas where giardiasis is endemic. [ABSTRACT FROM PUBLISHER]

Seven patients with hypoalbuminaemia and extensive jejunoileal Crohn's disease were treated with an elemental diet for 28 to 56 days. Over this time there was an increase in total plasma proteins from mean of 49.1 to 59.0 g/l and a mean rise in serum albumin from 20.7 to 30.0 g/l (P less than 0.05). In addition, there was a 47% mean reduction in plasma protein loss into the gastrointestinal tract and a rise in blood lymphocyte count in all patients (P less than 0.05). These results suggests that, as well as providing nutritional support, elemental diets reduce protein and lymphocyte loss from the diseased intestine. [ABSTRACT FROM PUBLISHER]

Pneumatosis cystoides intestinalis (PCI) is an uncommon condition of unknown aetiology. Bacterial gas production may be an important aetiological factor, but experimental evidence in humans has been lacking. We have studied breath hydrogen excretion as an index of bacterial gas production in 12 patients with PCI and have shown that four out of five with demonstrable cysts produced unusually high levels of hydrogen while fasting. This abnormality has not been previously reported. One patient showed resolution of PCI after antibiotic treatment. These findings confirm the importance of bacterial gas production in the pathogenesis of PCI. [ABSTRACT FROM PUBLISHER]

Reports several issues related to medical science as of February 1987. Education of elusive orthopaedic senior house officers; Comparison of the ulcerogenicity of piroxicam problems and non-steroidal anti-inflammatory drugs; Analysis of lung cancer and passive smoking.

A series of benzodioxolyl carbamates has been prepared and evaluated in the laboratory for insecticidal activity against a range of ten species. The results indicated that this was optimal with the 4-benzodioxolyl carbamates with a 2,2-dialkyl substitution. The most promising of these on the basis of cost-effectiveness was 2,2-dimethyl-1,3-benzodioxol-4-yl methylcarbamate, bendiocarb, which is being developed commercially for the control of household pests. [ABSTRACT FROM AUTHOR]

Oxygen administration via a nasal cannula incorporating a small collapsible reservoir (Oxymizer, Chad Therapeutics Inc, California) was compared with delivery via a standard nasal cannula. Twelve patients with chronic, stable hypoxaemia (arterial oxygen tension less than 60 mm Hg (8.0 kPa)) were studied. Transcutaneous oxygen and carbon dioxide tensions were recorded by skin electrodes and oxygen saturation by ear oximetry. Baseline measurements during the breathing of air were compared with those made during the breathing of oxygen at flow rates of 0.5, 1.0, and 2.0 l/min via each device. Increases in saturation and transcutaneous oxygen tension were significantly greater at each flow rate with the reservoir device than with the conventional cannula. To produce similar improvements in oxygenation the reservoir device required an oxygen flow rate about half that of the conventional cannula. Use of the reservoir device may reduce the inconvenience and perhaps the cost of supplying domiciliary oxygen, and prolong the time during which patients may rely on a portable cylinder. [ABSTRACT FROM AUTHOR]