Pyrus calleryana extracts reduce germination of native grassland species, suggesting the potential for allelopathic effects during ecological invasion

Invasive plant species' success may be a result of allelopathy, or the release of secondary metabolites that are harmful for surrounding plant species. Allelopathy can be mediated through the abiotic environment by chemical sorption or transformation, so the substrate on which interactions occur can lead to differential outcomes in allelopathic potential. One aggressive invader, Pyrus calleryana, has become dominant in many ecosystems throughout Eastern US, and has reduced the abundance of native species where it invades. Thus, our goal was to identify if P. calleryana had allelopathic potential by testing the impact of leaf and flower leachate on gemination of six common grassland species (three grasses and three forbs) in either sterilized sand or field collected soils. Germination of five out of six tested species was reduced by P. calleryana leaf litter, with weaker impacts from flower leachate. This suggests that allelopathy is one mechanism driving the success of P. calleryana and that allelopathic effects may change with plant phenology. For instance, P. calleryana has late leaf senescence in the fall and copious blooming in the spring that may elongate the timeframe that allelopathic inhibition can occur. Further, germination was higher in sand than in soil, suggesting that the context of the abiotic environment can mediate this relationship. In our study, two grass species that could be overabundant in restored grasslands had higher germination rates in soil than sand and one was not altered by P. calleryana suggesting that this relationship could further promote the overabundance of grass species. Taken together, P. calleryana likely inhibits the germination of native species where it invades, but there is context dependency of this relationship with both soil chemistry and seasonality.

Termite sensitivity to temperature affects global wood decay rates

Deadwood is a large global carbon store with its store size partially determined by biotic decay. Microbial wood decay rates are known to respond to changing temperature and precipitation. Termites are also important decomposers in the tropics but are less well studied. An understanding of their climate sensitivities is needed to estimate climate change effects on wood carbon pools. Using data from 133 sites spanning six continents, we found that termite wood discovery and consumption were highly sensitive to temperature (with decay increasing >6.8 times per 10°C increase in temperature)-even more so than microbes. Termite decay effects were greatest in tropical seasonal forests, tropical savannas, and subtropical deserts. With tropicalization (i.e., warming shifts to tropical climates), termite wood decay will likely increase as termites access more of Earth's surface.

Accounting for local adaptation in ectomycorrhizas: a call to track geographical origin of plants, fungi, and soils in experiments

Local adaptation, the differential success of genotypes in their native versus foreign environments, can influence ecological and evolutionary processes, yet its importance is difficult to estimate because it has not been widely studied, particularly in the context of interspecific interactions. Interactions between ectomycorrhizal (EM) fungi and their host plants could serve as model system for investigations of local adaptation because they are widespread and affect plant responses to both biotic and abiotic selection pressures. Furthermore, because EM fungi cycle nutrients and mediate energy flow into food webs, their local adaptation may be critical in sustaining ecological function. Despite their ecological importance and an extensive literature on their relationships with plants, the vast majority of experiments on EM symbioses fail to report critical information needed to assess local adaptation: the geographic origin of the plant, fungal inocula, and soil substrate used in the experiment. These omissions limit the utility of such studies and restrict our understanding of EM ecology and evolution. Here, we illustrate the potential importance of local adaptation in EM relationships and call for consistent reporting of the geographic origin of plant, soil, and fungi as an important step towards a better understanding of the ecology and evolution of EM symbioses.

Isolation of megakaryocytes from human placentae

Shedding of cytoplasm from circulating megakaryocytes (MKs) within the pulmonary vasculature suggests the lungs are an important site for normal platelet production. Fetal lungs receive only a minor fraction of the circulating blood volume. The placenta may act as a site for intrauterine platelet formation. Isolation of MKs from fetal vessels within the placenta has not been previously reported. Immediately after delivery, 3 human placentae were subjected to forward and retrograde perfusion across the placental capillary bed on the fetal side. MKs in perfusates were harvested by 'whole blood filtration' and identified by morphological and immunochemical methods. All perfusates yielded MKs. Qualitatively MKs with copious cytoplasm were more commonly found in perfusates collected from fetal arteries compared with those from fetal veins. This is consistent with filtration of MKs and fragmentation of their cytoplasm within the placental microcirculation to produce platelets. Perfusion of human placentae followed by filtration of perfusates is a useful technique for harvesting fetal MKs and permitting further elucidation of their physiological role.

Evolution of virulence in Fusarium oxysporum f. sp. vasinfectum using serial passage assays through susceptible cotton

Fifty strains of Fusarium oxysporum, recovered from rhizosphere soil around native Gossypium species and found to be mildly virulent on cotton (Gossypium hirsutum), were used to assay the propensity for evolution of virulence using serial passage assays through cotton. Only one lineage A strain, 2613, successfully completed 10 successive passages, while all others lost the ability to cause foliar disease symptoms at various stages during this process. Based on 46 amplified fragment length polymorphism (AFLP) markers generated with four EcoRI x MseI primer combinations, mutants were identified in offspring isolates from strain 2613 regardless of whether serial passages occurred in cotton or on water agar, suggesting the occurrence of spontaneous mutations. Significantly increased virulence was observed in the offspring isolates generated on cotton, while no increasing virulence was found in those obtained on water agar, suggesting that the evolution of virulence in F. oxysporum f. sp. vasinfectum is associated with the presence of cotton. No clear correlation was observed between the AFLP mutations and increased virulence in this study.

Radionuclide calibrator comparisons and quality improvement in nuclear medicine

The traceability of activity measurements performed during the development phase of the radiopharmaceutical and in its clinical application is essential for establishing the comparability of clinical results reported in the nuclear medicine field. This paper presents and discusses the evaluation over time of the quality of activity measurement results obtained in Cuban nuclear medicine, on the basis of statistical samples taken during the radionuclide calibrator comparison program. An attempt is also made to evaluate the role played by such comparisons in quality measurement improvement in nuclear medicine, on the basis of results obtained in a number of countries and published by several authors over a period of time. Specifically, improvements of the measurement performance over time assessed by such exercises were found dissimilar in magnitudes for different countries. Two phases could be distinguished in the improvement process over time. Firstly, a fast improvement can be obtained resulting from the improvement in measurement accuracy of devices. After that, the achievement of new and sustained improvements goes slowly and requires an application of quality assurance programs where the qualification upgrading of personnel become an essential point.

International guidance on the establishment of quality assurance programmes for radioactivity measurement in nuclear medicine

A new guidance document for the implementation of quality assurance (QA) programmes for nuclear medicine radioactivity measurement, produced by the International Atomic Energy Agency, is described. The proposed programme is based on the principles of ISO 17025 and will enable laboratories, particularly in developing countries, to provide consistent, safe and effective radioactivity measurement services to the nuclear medicine community.

Comparison of strontium-89 solution sources in UK hospitals, 2003

Concerns have been raised within the nuclear medicine field about the accuracy of measurements of 89Sr. The 85Sr impurity present in the 89Sr solution has a significant effect on the response of radionuclide calibrators used in hospitals. A comparison was conducted between the National Physical Laboratory (NPL) and the UK hospital physics community. Only 58% of the results were within 5% of the NPL value. Work at NPL has resulted in correction factors for the NPL secondary standard radionuclide calibrator and for Capintec calibrators, which will produce a significant improvement in performance.

Some results of a simulated test for administration of activity in nuclear medicine

This paper describes the results obtained using a simulated test for administration of activity in nuclear medicine between 2002 and 2004. Measurements in the radionuclide calibrator are made during the different stages of the procedure. The test attempts to obtain supplementary information on the quality of the measurement, with the aim of evaluating in a more complete way the accuracy of the administered activity value compared with the prescribed one. The participants' performance has been assessed by means of a statistical analysis of the reported data. Dependences between several attributes of the simulated administration tests results are discussed. Specifically, the proportion of satisfactory results in the 2003-2004 period was found to be higher than in 2002. It reveals an improvement of the activity administration in the Cuban nuclear medicine departments since 2003.

Comparison of radioactivity measurements with radionuclide calibrators in the Republic of Korea

Recognizing the importance of comparisons of radionuclide calibrators in nuclear medicine and the need to provide access to activity standards that are traceable to the international measurement system, the Korea Food & Drug Administration (KFDA) as a national secondary standard dosimetry laboratory (SSDL), started a comparison program in 2002. The first two comparisons were conducted with (131)I (71 participants) and (99m)Tc (72 participants). The results indicated that only 61% of reported activities for (131)I and 65% for (99m)Tc were within +/-5% of the correct value. These numbers increased to 84% for (131)I and 83% for (99m)Tc when a +/-10% limit was applied. Follow-up action on those calibrators with results outside the +/-10% limits only produced a small improvement. There was also a marked difference in performance between the various calibrator types used. The results have shown that such comparisons are necessary to improve the quality of the measurements and to identify those radionuclide calibrators that are not functioning correctly.

Half-life data--a critical review of TECDOC-619 update

An accurate knowledge of selected nuclear decay data is critical to a wide range of processes involving radionuclides. An IAEA publication in 1991 was dedicated to the evaluation of half-lives and specific gamma-ray emission probabilities for 39 selected radionuclides considered to be important for detector efficiency calibrations. A new exercise was initiated in December 1998 to update this previous evaluation and to include a number of new radionuclides of interest; 62 radionuclides were considered along with specific parent-daughter combinations (to give a total of 64 radionuclides). That work is now being completed and a new set of recommended data is being prepared for publication. A critical comparison of the 1991 and 2003 half-life data suggests that there has not been any significant improvement in the accuracy of the recommended data. The possible reasons for this situation are discussed together with the evaluation procedure and the quality of the available data. Proposals are made for concerted actions that could lead to a significant improvement in these recommended half-life data.

MRA calibration and measurement capabilities--radioactivity

The practical realisation of the Mutual Recognition Arrangement relies on its two main Appendices, B and C. Appendix B relates to the equivalence of national measurement standards. The dissemination of these standards is achieved by the provision of physical standards and measurement services, where the associated measurement values are traceable to the SI. Appendix C specifies the quantities and ranges for which participating institutes recognise the validity of calibration and measurement certificates issued by other participating institutes and these are detailed in the database devoted to these standards and services, commonly referred to as calibration and measurement capabilities. Each participating institute has the opportunity to submit entries, via its Regional Metrology Organisation (RMO), to the database but, in order for users to be able to make informed choices, it is important that the data are entered to a common standard. The Joint Committee of the RMOs and the Bureau International des Poids et Mesures is responsible for the coordination of data provided by the RMOs. It is for individual RMOs to ensure the correctness of their own entries and to review and comment on those from others. This paper details that process and describes the various entries in the tables. It also addresses some of the remaining issues that still need to be resolved, in particular, the magnitudes of uncertainties and the need for supporting comparisons, both of which still present some significant problems.

Secondary standardisation of 95mTc

The radionuclide 95mTc, which has a half-life of 61(2)days and emits a number of gamma-rays, may be used in radiochemical analysis as a yield tracer for the long-lived fission product 99Tc. In this work, we present (i) the production of 95mTc via an (alpha, 2n) reaction with stable 93Nb (a method which does not result in the production of any 97mTc, 98Tc or 99Tc), (ii) the chemical separation of 95mTc from niobium via coprecipitation, liquid-liquid extraction and liquid chromatography, and (iii) the secondary standardisation of 95mTc with high-resolution gamma-ray spectrometry and an ionisation chamber system.

Establishing equivalence for activity standards of short-lived radionuclides using the NPL secondary standard radionuclide calibrator

Conventional comparison techniques used between National Metrology Institutes are not practicable for short-lived radionuclides because of geographical separations and transport difficulties. The NPL Secondary Standard Radionuclide Calibrator provides an alternative approach and a comparison was conducted with 18F to investigate its feasibility. The exercise was successful and the paper details the protocol used, the quality assurance mechanisms introduced to underpin the comparison and an analysis of the results. It was also demonstrated that this approach could be linked to the BIPM SIR system. Recommendations are presented for the extension of this work to other suitable, short-lived radionuclides.

Primary standardisation of 204Tl using the efficiency tracing method

The electron-capture and beta(-) -emitting radionuclide 204Tl has been known from previous experience to show discrepancies between different methods of standardisation. Source preparation is also difficult due to the complex chemistry of thallium. The Bureau International des Poids et Mesures (BIPM) intercomparison held in 1997, showed discrepancies of up to 10% between measurements of solid sources and liquid scintillation methods. These problems have been the subject of a BIPM CCRI(II) working group since 1999. This paper presents the results from a primary standardisation of a 204Tl solution using 4pibeta-gamma coincidence counting and liquid scintillation counting. The tracer technique was used for the 4pibeta-gamma coincidence counting, where 204Tl was traced with 134Cs and 60Co. The extrapolation to 100% beta-efficiency was performed by three different approaches: foiling, adding carrier and measuring sources of different initial masses. The results showed that tracing with 60Co and using external foiling gave the same result as obtained by liquid scintillation counting. A comparison of the results achieved by the different methods of measurement, tracers and methods for extrapolation is presented and discussed in this paper.

Syringe calibration factors for the NPL Secondary Standard Radionuclide Calibrator for selected medical radionuclides

Before a radiopharmaceutical is administered to a patient, its activity needs to be accurately assayed. This is normally done via a radionuclide calibrator, using a glass vial as the calibration device. The radionuclide is then transferred to a syringe and it is now becoming common practice to re-measure the syringe and use this value as the activity administered to the patient. Due to elemental composition and geometrical differences, etc. between the glass vial and the syringe, the calibration factors are different for the two containers and this can lead to an incorrect activity being given to the patient unless a correction is applied for these differences. To reduce the uncertainty on syringe measurements, syringe calibration factors and volume correction factors for the NPL Secondary Standard Radionuclide Calibrator have been derived by NPL for several medically important radionuclides. It was found that the differences between the calibration factors for the syringes and glass vials depend on the energies of the photon emissions from the decay of the radionuclides; the lower the energy, the greater the difference. As expected, large differences were observed for 125I (70%) and only small differences for 131I. However, for radionuclides such as 99mTc and 67Ga, differences of up to 30% have been observed. This work has shown the need for the use of specifically derived syringe calibration factors as well as highlighting the complexity of the problem with regard to syringe types, procurement, etc.

NPL secondary standard radionuclide calibrator. Syringe calibration factors for radionuclides used in nuclear medicine. National Physical Laboratory

The measurement of the activity of a radiopharmaceutical administration to a patient is normally achieved via the use of a radionuclide calibrator. Although these radionuclides are normally measured initially in a standard glass vial, an aliquot of the solution is then usually withdrawn into a syringe prior to the administration. Both for general quality assurance good practice and for additional guarantees for patient safety, a confirmatory measurement of the syringe is almost obligatory Because of the different geometries and elemental compositions between plastic syringes and glass vials, the calibration factors for syringes may well be significantly different from those for the glass containers. The magnitude of these differences depends on the energies of the emitted photons. A variety of syringes typically used in hospital administrations, and covering a range of volumes and manufacturers, were obtained. The results obtained were compared to those for glass vials and show the large errors that can be produced by ignoring these differences in container format.

Standardization and decay data of 237Np

This paper reports contributions from participants in the EUROMET project (No. 416) which was entitled "237Np research into problems relating to purification, characterization and standardization". Primary standardizations were made by the defined low solid angle, coincidence, 4pi alpha, 2pi alpha and liquid scintillation counting methods. Secondary standardizations were made with calibrated gamma-ray spectrometers. Absolute X-ray, gamma-ray and alpha-particle emission probabilities were also determined. The results for the successful conclusion of both primary and secondary standardization are presented together with the values for alpha-particle and gamma-ray emission probabilities determined in this exercise. Several significant inconsistencies remain with the gamma-ray emission probabilities, and these are highlighted.

Standardisation of 11C

The increasing use of positron emission tomography for medical imaging and the availability of short-lived positron emitters has raised concerns about the accuracy of calibration of secondary standard measurement systems and the viability of using a single long-lived positron emitter as a reference calibration source for all positron emitters. Potential problems arise because the 511 keV quanta arising from positron annihilation are not generally produced at the same point as the original disintegration. In addition, the secondary standard may also be responsive to the associated bremsstrahlung radiation. The magnitude of both effects depends on the positron end-point energy. In order to resolve these problems, it is necessary to produce absolute standards of these positron-emitting radionuclides and the work presented here details the results of such work with 11C.

Calibration of the NPL secondary standard radionuclide calibrator for 125I seeds used for prostate brachytherapy. National Physical Laboratory

In the therapeutic use of radionuclides, by far the most rapid growth in recent years is that of 125I seeds used for the treatment of prostate cancer. Large numbers of these seeds are used in each treatment and there is a need for a simple but accurate means of confirming their dose rates. This mechanism requires a transfer device for which the calibration factors are traceable to national standards. The NPL secondary standard radionuclide calibrator, because of its guaranteed reproducibility and traceable calibration procedure, is ideally suited for this purpose. A series of characterisation measurements have been performed on the NPL radionuclide calibrator in order to estimate the uncertainty levels that can be achieved and these are presented together with the relevant calibration factors for some typical seeds.

Thorium in the workplace: results from a European-based measurement comparison project

A Series of comparisons were conducted to test the capabilities of a range of metrological techniques and analytical laboratories engaged in the assay of thorium in the workplace. The results of these exercises are presented together with the decision criteria used to determine whether results are significantly different from the true value. The discussion highlights those aspects which warrant closer and further attention.

Nuclear data used in the analysis of thorium in the workplace

The analysis of thorium in the workplace can be achieved using a variety of metrological techniques. The uncertainty on the final measured values will include components that arise from the uncertainties in the nuclear data that are used. These data include half-lives, branching ratios and gamma ray emission probabilities. It is important that a common, consistent and reliable data set is used in order to minimise the potential differences between analytical results. With particular reference to the problems associated with thorium analysis, some of the various sources of nuclear data are discussed and a recommended set of data is proposed.

The EC Thematic Network on the Analysis of Thorium and its isotopes in Workplace Materials

Accurate measurements of workplace exposure to 232Th and its progeny are required to estimate internal radiation doses received by persons working with thorium-containing materials. However, a small intercomparison carried out in the mid-nineteen nineties raised doubts about the reliability of results obtained by methods available for measurement of thorium. An EC-funded thematic network was therefore established to bring together experts in the field of thorium analysis in order to coordinate research activity and identify best analytical practice. requirements for reference materials. etc. This network has now successfully completed its work programme. which included a survey to determine future research needs; a series of intercomparisons to test the performance of methods for measuring thorium in workplace materials, and a workshop held to promote best practice and transfer information to regulatory authorities and industry. Results of the work have been used to make various recommendations concerning future needs in this field.

Thorium in the workplace: the preparation and validation of comparison samples for a European-based measurement comparison project

The quality of any comparison exercise depends critically on the quality. accuracy and fitness for purpose of the comparison samples. The comparisons were designed to move progressively from the testing of the analysis capabilities for relatively simple. aqueous solutions through to the more complex natural matrix materials encountered in the workplace. In each case, it was imperative that the comparison samples were prepared and validated in such a way as to ensure traceability of their activity values to national and international standards of radioactivity, to enable a reasonable estimate to be made of the uncertainty on those values and to ensure homogencity both within and between samples. The processes involved are discussed.

Thorium in the workplace measurement intercomparison

The monitoring of radionuclides in the nuclear industry has been recognized as the most straightforward way of assessing health and safety issues associated with the exposure of the workforce to potentially harmful radiation doses. Much of this is achieved by measurements in the workplace itself and by the bioassay and monitoring of workers in the industry. However, there also exists a significant 'non-nuclear' industry where workers are exposed to radioactive materials, for example where this involves thorium, which is made wide use of in the aerospace and other high technology industries. As such work involves the processing of thorium bearing materials, the workforce is potentially exposed to 232Th and its daughter nuclides. Thus, to monitor the workforce effectively, it is important to be able to measure both 232Th and the decay products of 232Th where they are in an unknown state of radioactive equilibrium and this is where monitoring laboratories may experience some difficulty. Accordingly, the Health and Safety Laboratory in the UK has organized a EC wide project on the monitoring of thorium in the 'non-nuclear' workplace; this project is currently ongoing. We report the results of the first intercomparison of this project involving two solutions of 232Th, one in radioactive equilibrium and one not in equilibrium with its daughters. The results are presented with some comments on how this intercomparison has progressed and how these first results will inform the rest of the project.

Standardisation of 210Pb

The standardisation of 210Pb is complicated by the presence of the daughters, 210Bi and 210Po. In addition, the low energies of the beta emissions from 210Pb make it difficult to obtain high detection efficiencies in an atmospheric proportional counter and hence produce the need for large extrapolations with consequential large uncertainties when extrapolating to unit efficiency with the conventional 4pi(PC)-gamma-coincidence technique. In order to produce a reliable standardisation, it is necessary to remove the daughter products. A solution of 210Pb was therefore chemically separated from its daughters and then standardised using the conventional 4pi(LS)-gamma-coincidence technique. The low energy (46 keV) and low emission probability (4%) of the associated photon emissions effectively rules out the possibility of using ionisation chambers as secondary standard transfer instruments for this nuclide. A germanium spectrometer therefore was calibrated for this purpose using 241Am as a normalising agent. The results of this work are presented together with an analysis of the standardisation uncertainties that can be achieved in practice.

Equivalence in radionuclide metrology

The harmonization of different National Measurement Systems depends on the ability to demonstrate Equivalence between them. The responsibility for establishing a procedure to achieve this lies with the International Committee of Weights and Measures (CIPM) and its associated Consultative Committees. In pursuit of these ends, a series of general recommendations and procedures have been developed by BIPM in order to achieve these objectives. Central to these recommendations is the concept of Key Comparisons which involve a series of comparison exercises both within and between the regional metrology organizations, such as EUROMET, NORAMET and APMP. Because of the unique nature of radioactivity standardization, this generalized procedure is, for practical purposes, impossible to apply in the field of radionuclide metrology. The remedy has been the development of a protocol which optimizes both the current effort available within existing National Metrology Institutes (NMIs) and the considerable amount of data from previous intercomparisons. This paper details this novel approach, provides practical examples, discusses potential problems and examines the way in which the programme will continue and expand.

Multiple forms and locations for the peripheral-type benzodiazepine receptor

The pharmacological effects of benzodiazepines are mediated through a class of recognition sites associated with the neuronal gamma-aminobutyric acidA (GABAA) receptor. A second class of benzodiazepine binding sites is found in virtually all mammalian peripheral tissues, in blood cells, and in glial cells in the brain, but its functions remain unclear. Although these peripheral-type benzodiazepine binding sites (PBBS) have been localized to the mitochondrial outer membrane in many tissues, a growing body of evidence suggests that they may also exist on the plasma membrane. Plasma membrane PBBS have been described in heart, liver, adrenal, and testis and on hemopoietic cells. In rat liver, the two subcellular forms of PBBS are found separately in two different subpopulations of cells. The discovery of a plasma membrane fraction of PBBS clearly has implications for some of its putative functions, including steroidogenesis, mitochondrial respiration, heme metabolism, calcium channel modulation, cell growth, and immunomodulation. This commentary reviews the evidence for two locations for the PBBS and discusses the relevance of mitochondrial and plasma membrane forms with regard to structure, molecular biology, and proposed roles.

Synthesis, biological activity, and SARs of pyrrolobenzoxazepine derivatives, a new class of specific "peripheral-type" benzodiazepine receptor ligands

The "peripheral-type" benzodiazepine receptor (PBR) has been reported to play a role in many biological processes. We have synthesized and tested a novel series of PBR ligands based on a pyrrolobenzoxazepine skeleton, in order to provide new receptor ligands. Several of these new compounds proved to be high affinity and selective ligands for PBR, and benzoxazepines 17f and 17j were found to be the most potent ligands for this receptor to have been identified to date. The SAR and the molecular modeling studies detailed herein delineated a number of structural features required for improving affinity. Some of the ligands were employed as "molecular yardsticks" to probe the spatial dimensions of the lipophilic pockets L1 and L3 in the PBR cleft and to determine the effect of occupation of L1 and L3 with respect to affinity, while other C-7 modified analogues provided information specifically on the hydrogen bonding with a putative receptor site H1. The new pyrrolobenzoxazepines were tested in rat cortex, a tissue expressing high density of mitochondrial PBR, and exhibited IC50 and Ki values in the low nanomolar or subnanomolar range, as measured by the displacement of [3H]PK 11195 binding. A subset of the highest affinity ligands was also found to have high affinities for [3H]PK 11195 and [3H]Ro 5-4864 binding in rat adrenal mitochondria. All the ligands in this subset are stimulators of steroidogenesis having similar potency and extent of stimulation as PK 11195 and Ro 5-4864 of steroidogenesis in the mouse Y-1 adrenocortical cell line.

Two cellular and subcellular locations for the peripheral-type benzodiazepine receptor in rat liver

Determination of ligand binding properties of the peripheral benzodiazepine receptor (PBBS) in liver, in hepatocytes, and in nonparenchymal cells demonstrated the presence of receptor-specific high-affinity binding in both hepatocyte and nonhepatocyte cells. Density gradient centrifugation showed that the high-affinity receptor in hepatocytes was localised to mitochondria, whereas in nonhepatocytes it was not mitochondrial, but with a possible biliary epithelial cell plasma-membrane location. Both receptors showed the peripheral-type specific high-affinity binding of PK 11195 and Ro5 4864 and could be photolabelled as 18 kDa proteins with [3H]PK 14105. Immunocytochemistry showed the presence of acyl-CoA binding protein, a putative endogenous ligand for the receptor, in both cell locations. Some other properties of the PBBS were investigated in liver. Diphosphatidyl glycerol had a strong inhibitory effect on receptor binding in both liver and adrenal, with Ro5 4864 more sensitive to inhibition than PK 11195. However, whereas soybean lipid and phosphatidyl serine increased the binding of both ligands to adrenal receptor, these lipids had no effect on liver, suggesting that liver PBBS may differ from the well-characterised adrenal PBBS in some of its protein conformation. Modulators of mitochondrial respiration that also influence intermembrane contact site formation were found to elicit no marked stimulatory or inhibitory effects on PBBS ligand binding in liver, a result also found for adrenal mitochondria, suggesting that the extent of contact site formation does not influence ligand binding and that the hepatocyte receptor may not play a role in regulating mitochondrial respiration. These two cellular and subcellular locations of the PBBS in liver and the different effect of phospholipids compared to other peripheral tissues may be important for the role(s) of PBBS in liver and also for the multiple roles ascribed to the receptor and to peripheral-type benzodiazepine ligands.

The fate of circulating megakaryocytes during cardiopulmonary bypass

Megakaryocytes with intact cytoplasm normally leave the bone marrow, enter central venous blood, and are filtered in the lungs. During cardiopulmonary bypass, large megakaryocytes are not filtered by the lungs and may not be removed in the extracorporeal circuit by arterial line filters. In such circumstances, they could enter the systemic circulation and block smaller cerebral vessels, resulting in neurologic impairment. To investigate the fate of circulating megakaryocytes during cardiopulmonary bypass, central venous blood and oxygenated blood samples before and after arterial line filtration (40 microns polyester screen filter) were obtained from 10 patients undergoing cardiopulmonary bypass. Megakaryocytes were isolated by whole blood filtration and identified by their characteristic structure after May-Grunwald-Giemsa staining. In preliminary studies, megakaryocyte identification was verified by immunolabeling. All samples contained megakaryocytes with copious cytoplasm. Their frequencies in central venous blood and oxygenated blood before and after the arterial line filtration (corrected for hemodilution) were 23.4 +/- 9.3 per milliliter (mean +/- standard error of the mean, range 3.1 to 89.7 per milliliter), 21.0 +/- 8.2 per milliliter (2.0 to 84.2 per milliliter) and 17.1 +/- 7.4 per milliliter (3.1 to 80.4 per milliliter), respectively. Megakaryocytes with scant or no visible cytoplasm were also observed. The results confirm that circulating megakaryocytes are a normal physiologic component. During cardiopulmonary bypass, megakaryocytes with copious cytoplasm (mean diameter 42.7 microns, range 22 to 78 microns) can pass through the extracorporeal circuit. In the absence of filtration by the lungs, these large cells have access to the systemic circulation. This study supports a possible role for circulating megakaryocytes in the development of cerebral dysfunction after cardiopulmonary bypass.

Calibration of the NPL secondary standard radionuclide calibrator for 192Ir brachytherapy sources

Safe and effective treatment with brachytherapy sources requires an accurate knowledge of the local tissue absorbed dose rate derived from the source reference air kerma rate. It is desirable that these air kerma rate measurements be traceable to national standards. The NPL has embarked on a programme that will enable the user to assay brachytherapy sources in a convenient manner prior to treatment. Calibration figures have been derived for the NPL secondary standard radionuclide calibrator for 192Ir brachytherapy sources manufactured by Amersham International plc. The calibration figures enable the user to accurately estimate the reference air kerma rate and activity of such sources by measuring the ionization chamber response. Calibration figures for other brachytherapy sources are also being derived.

Isolation of circulating megakaryocytes in man

Recovery of the small numbers of megakaryocytes (MKs) known to be present in normal blood is difficult because of their low frequency. Isolation of circulating MKs was achieved using a modified filtration system in which untreated blood was passed through 5 microns polycarbonate membranes. MKs were retained while most other blood cells passed through the membranes. Four groups of MKs were identified in May Grünwald-Giemsa stained filters of blood from peripheral, central and umbilical veins and umbilical arteries. Type 1 MKs were nuclei with no visible cytoplasm. Types 2, 3 and 4 were nuclei with increasing amounts of cytoplasm. Type 4 MKs, possessing copious cytoplasm, were rarely isolated from peripheral venous blood but were more regularly encountered in central venous and cord blood. Filtration of whole blood through polycarbonate membranes is a useful technique for the isolation of circulating MKs, which are a normal physiological occurrence. Their presence is consistent with the production of platelets in the placenta during intra-uterine life, and subsequently in the pulmonary circulation.

Electrical impedance assessment of muscle changes following exercise

Electrical impedance measurements have been assessed as a method of detecting changes in striated muscle following vigorous exercise. Transverse and longitudinal resistivities of the calf and thigh have been measured before and after four subjects ran a half marathon (21 km). No changes were observed in longitudinal resistivity but transverse resistivity rose by an average of 7% following the race. These results are consistent with changes in the muscle fibre membranes or interstitial fluid content.

Megakaryocyte ploidy in thrombocytosis: improved microdensitometric measurements with a new image analysis system

Megakaryocyte (MK) nuclear deoxyribonucleic acid (DNA) content was measured on a new image analysis system. Feulgen-stained bone marrow aspirate smears were analysed from 9 patients with thrombocytosis. Average optical density (OD) of stained nuclei was evaluated by pixel discrimination over 128 grey levels. Projected nuclear area was delineated manually. The product of these two parameters gave an index of nuclear DNA content. Neutrophils were used as 2N reference cells. Reproducibility of OD, nuclear area and their product was excellent for individual cells (CV less than 2.0% for MKs, less than 4.0% for neutrophils). The average CV for DNA content of 18 groups of 10 neutrophils was 5.5% (range 3.0-9.7%). A significant linear regression existed between MK nuclear area and DNA content (p much less than 0.001) for 627 MKs in essential thrombocythaemia (ET) and 346 MKs in reactive thrombocytosis (RT). Compared with RT, more 8N and 64N MKs were seen in ET (p less than 0.05). 128N MKs were unique to ET. Image analysis of MK ploidy may assist the clinical discrimination between primary and secondary thrombocytosis.

Two subcellular locations for peripheral-type benzodiazepine acceptors in rat liver

Subcellular fractionation of rat liver by differential centrifugation showed the mitochondrial fractions to have the greatest enrichment of 'peripheral-type' benzodiazepine acceptor. Two peaks of acceptor sites were found on isopycnic density-gradient centrifugation, one peak (rho = 1.19 g/ml) corresponding to the peak of mitochondria as judged by marker enzyme distribution and by transmission electron microscopy, and the other peak (rho = 1.17 g/ml) which is not mitochondrial as judged by the lack of mitochondrial enzyme markers. Whereas the density of the mitochondrial acceptor was sensitive to sonication and was shown to have an outer-membrane location, the density of the non-mitochondrial acceptor was insensitive to sonication. The non-mitochondrial acceptor was shown not to be associated with Golgi, lysosomes, rough endoplasmic reticular microsomes, peroxisomes, or some types of plasma membranes, as judged by differences in the distribution of marker activities. No enrichment of benzodiazepine acceptor was found in the purified nuclear fraction. Both acceptors were shown to be peripheral-type high-affinity acceptors as judged by ligand specificities and by photoaffinity labelling.

The accuracy of surface-contamination measurements; survey of UK hospitals, 1986

In response to a number of concerns expressed at both national and international levels, the National Physical Laboratory (NPL) conducted a survey of UK hospitals and associated Regional Radiation Protection Services. Sources of surface contamination were distributed and participants were requested to measure these and interpret the relevant responses in terms of emission and activity per unit area. The analysis of the returns demonstrates that the vast majority of results was significantly in error and that the quality of radiation protection may be impaired.

A partial decay scheme study of 82Rb and consequences for radiation dose measurements

Measurements of the relative emission rates of the 776 keV gamma ray, the positrons and the K x-rays in the decay of 82Rb have been repeated. This has led to the finding that the gamma ray to positron ratio is 0.1578 +/- 0.0019 and that the 776 keV gamma-ray probability per decay is (15.12 +/- 0.18)%.

Intercomparison of radionuclide calibrator measurements in U.K. hospitals

The Life Sciences Working Group of the International Committee for Radionuclide Metrology had received various reports of users of radionuclide calibrators experiencing problems in obtaining accurate measurements of radionuclide activity. Working Group members were encouraged to initiate surveys in their own countries to assess the magnitude of these problems. The results of the survey in the United Kingdom are given.

Radioassay problems associated with the clinical use of a 82Rb radionuclide generator

The short-lived positron emitting radionuclide 82Rb (t1/2 1.27 min) is conveniently available from a 82Sr/82Rb generator system. The parent nuclide (t1/2 25.5d) produced from the spallation of molybdenum, has associated with it varying quantities of other long-lived strontium radionuclides, namely 85Sr, 89Sr and 90Sr. It is important therefore in the clinical use of such material that the levels of strontium radionuclides being administered to patients is carefully assayed and controlled. The problems associated with these measurements are discussed with special reference to the radiation dose received by the patient and the problems in resolving overlapping peaks with different FWHMs.

Kinetic mechanism of the aliphatic amidase from Pseudomonas aeruginosa

The kinetic constants for hydrolysis and transfer (with hydroxylamine as the alternate acceptor) of the aliphatic amidase (acylamide amidohydrolase, EC 3.5.1.4) from Pseudomonas aeruginosa were determined for a variety of acetyl and propionyl derivatives. The results obtained were consistent with a ping-pong or substitution mechanism. Product inhibition, which was pH dependent, implicated an acyl-enzyme compound as a compulsory intermediate and indicated that ammonia combined additionally with the free enzyme in a dead-end manner. The uncompetitive activation of acetamide hydrolysis by hydroxylamine and the observation that the partitioning of products between acetic acid and acetohydroxamate was linearly dependent on the hydroxylamine concentration substantiated these conclusions and indicated that deacylation was at least partially rate limiting. With propionamide as the acyl donor apparently anomalous results, which included inequalities in certain kinetic constants and a hyperbolic dependence of the partition ratio on the hydroxylamine concentration, could be explained by postulating a compulsory isomerisation of the acyl-enzyme intermediate prior to the transfer reaction.