Isomérisation des 5-bromo-5,6-dihydro-6-hydroxythymidines. Préparation des formes anomères de la thymidine et de la 1-(2-désoxy-D-érythro-pentofuranosyl)thymine

The trans 5-(R), 6-(R) and 5-(S), 6-(S) diastereoisomeric forms of 5-bromo-5,6-dihydro-6-hydroxythymidine were obtained by the action of bromine upon thymidine in aqueous solution. Treatment of these compounds with warm M hydrobromic acid both rearranges the sugar moiety and cleaves the glycosylamine bond; the yields of both processes were determined. Reduction of the halohydrins gave three isomeric compounds derived from thymidine : 1-(2-deoxy-α-D-erythro-pentofuranosyl)thymine, 1-(2-deoxy-β-D-erythro-pentopyranosyl)thymine and 1-(2-deoxy-α-D-erythro-pentopyranosyl)thymine. These isomerisations were also shown in the treatment of thymidine with hydrobromic acid, but, in the latter case, the process is less productive than in the former one. A mechanism for these reactions is discussed.     

Influence du piclorame sur l'activité phénylalanine-ammoniac lyase de Nicotiana tabacum induite par la réaction d'hypersensibilité au virus de la mosaïque du tabac

In Nicotiana tabacum var. Xanthi n.c. phenylalanine ammonia lyase (PAL) activity, which increases significantly during the hypersensitivity reaction to tobacco mosaic virus (TMV), is only partially affected when plants are treated with piclorame, which is known to be an inhibitor of PAL in vivo. Using piclorame together with TMV, it has been possible to distinguish between that increase in PAL activity due to the virus and that dependent on the photoperiod.     

Impact d’une réduction d’activité sur la mesure de la fraction d’éjection du ventricule gauche sur caméra D-SPECT

IntroductionRadionuclide ventriculography provides a reproducible measurement of the left ventricular fraction ejection (LVEF) but with a significant body radiation (effective dose of 5,9 mSv for the injection of 850 Mbq of ^99mTc). The highly sensitive semi-conductor (CZT) cameras could allow decreasing the injected activity by a factor 3, similarly to that of myocardial perfusion imaging. Our study was aimed to determine whether the LVEF measurement provided by radionuclide ventriculography on the CZT D-SPECT camera is impacted by a 70% reduction in recorded counts.Materials and methodsAfter the in vivo labeling of red blood cells with 850 MBq of ^99mTc, 49 patients completed a conventional 2D recording (Conv-2D) on Anger camera followed by a 3D recording on the D-SPECT camera (3D-100%). The CZT recordings of all projections were subsequently shortened to 30% of their initial durations (3D-30%) in order to assess the LVEF measured with a 70% reduction in recorded counts.ResultsMean LVEF values were 62.7 ± 11.1% on Conv-2D and higher on both 3D-100% (66.8 ± 14.8%, P < 0.001) and 3D-30% (66.3 ± 15.7%, P < 0.001). The correlation coefficients with the LVEF determined with the reference Conv-2D method were equivalents for 3D-100% (r² = 0.73) and 3D-30% (r² = 0.70) and with a similar level of overestimation for the highest LEVF values.ConclusionA 70% reduction in recorded counts does not significantly impact the LVEF measured with radionuclide ventriculography on the CZT D-SPECT camera. These values are coherent with those obtained with the reference 2D method but with a clear overestimation for the highest LVEF values.     

Influence de la rhTSH sur la fixation du 18 FDG dans une population de 42 patients avec cancer différencié de la thyroïde suspect de récidive

PurposeThe role of positron emission tomography with 18 fluoro-deoxy-glucose (FDG-PET) in case of differentiated thyroid carcinoma recurrence is established. However, the influence of TSH levels on 18 FDG is still discussed. Our study aims at comparing respective performances of FDG-PET performed at low TSH levels and under rhTSH stimulation, when a recurrence of a thyroid carcinoma is suspected.Material and methodsForty-two patients have been included, in a prospective way; each of them has been explored by FDG-PET at low (PET1) and high TSH levels with Thyrogen^® (PET2). The number of hypermetabolic foci, the intensity of uptake, both visual and with Standardized Uptake Values (SUV) have been compared.ResultsPET1: 82 foci were detected, including 75 true positive (TP) and seven false positive (FP). Sensitivity by lesion is 85.23 and 58.6% on a patient basis. Twelve pathological sites, not visualized (false negative) in PET1, were seen under stimulation. PET2: 89 foci were detected, including 87 TP and two FP; two tumoral sites visualized with PET1 are not detected. Sensitivity by lesion is 97.75 and 75.9% on a patient basis. SUV are significantly higher under stimulation. In three patients, therapeutic strategy has been modified, based on PET2 data.ConclusionStimulation by rhTSH improves FDG-PET performances. Therefore, it is justified to resort to it in case of recurrence of differentiated thyroid carcinoma, when the usual workup is negative.     

Datation par la méthode 40Ar / 39Ar de la couche de cendres volcaniques (couche VI) de Dmanissi (Géorgie) qui a livré des restes d'hominidés fossiles de 1,81 Ma

The exceptional prehistoric site of Dmanisi, in the South of Georgia, has yielded several hominid fossil remains, including three skulls and three mandibles assigned to Homo ergaster, in volcanic ashes and fluvio-lacustrine sands lying directly on a basalt flow. These levels also contain an archaic lithic industry consisting of pebble tools, cores and flakes, and large mammal remains attributed to the beginning of the Lower Pleistocene (Biharian). The basalt flow has been previously dated to about 1.85 Ma, but the overlying volcanic ash level had not yet been dated. In this paper, we present ⁴⁰Ar/³⁹Ar dating of plagioclase and glass from the volcanic ash level that has yielded Quaternary fauna, lithic artefacts and several human remains, which gives an age of 1.81±0.05 Ma. The subcontemporaneity of Hominid presence and volcanic ash deposition makes Dmanisi the oldest prehistoric site currently known in Europe and proves human presence at the gates of Europe 1.81 Ma ago. To cite this article: H. de Lumley et al., C. R. Palevol 1 (2002) 181–189.     

Cinétiques de la fixation du 18F-FDG dans les structures cérébrales : faisabilité et résultats préliminaires

ObjectDynamic positron emission tomography (dyn-PET) acquisitions using the radiotracer ¹⁸F-deoxyglucose (¹⁸F-FDG) are mainly developed in research studies of brain PET in kinetic modelling to determine the local glucose consumption rate. This procedure is difficult to establish, due to its requirement for blood sampling. Here, we propose a simple approach to constructing time–activity curves (TACs) for four different brain structures (the arterial & venous regions and grey & white matter) based on direct image measurements on chronologically reconstructed image volumes of regions of interest.Materials and methodsWe applied our processing on 14 control subjects to extract their physiological state. We defined the reference ¹⁸F-FDG kinetic curves as a “population averaged TAC” for four structures. To increase the curves accuracy, our method included the evaluation of two normalization based on the integral of the activity curve in the arteries and the veins.ResultsThe method showed discrimination between artery, venous, grey and white matters. The two normalization methods significantly reduce the dispersion for the grey and white matter curves and that venous normalization showed the best overall efficiency.ConclusionWe have designed and evaluated an approach for directly defining PopAv_TACs which are representative of given anatomical structures.     

Les carcinomes papillaires de la thyroïde révélés par examen TEP/TDM au 18F-FDG : à propos de deux cas et revue de la littérature

The authors report the cases of two patients followed up for Hodgkin lymphoma, whose control PET/CT during chemotherapy revealed incidental papillary thyroid carcinoma as hypermetabolic thyroid foci. These incidental uptakes of ¹⁸F-FDG in the thyroid gland are rarely encountered in day-to-day practice of oncological PET/CT. However, they deserve an exploration to determine their etiology.