silicon and Hypoxia

The syntheses of new nitroimidazole compounds using silicon-[(18)F]fluorine chemistry for the potential detection of tumor hypoxia are described. [(18)F]silicon-based compounds were synthesized by coupling 2-nitroimidazole with silyldinaphtyl or silylphenyldi-tert-butyl groups and labeled by fluorolysis or isotopic exchange. Dinaphtyl compounds (6, 10) were labeled in 56-71% yield with a specific activity of 45 GBq/μmol, however these compounds ([(18)F]7 and [(18)F]11) were not stable in plasma. Phenyldi-tert-butyl compounds were labeled in 70% yield with a specific activity of 3 GBq/μmol by isotopic exchange, or in 81% yield by fluorolysis of siloxanes with a specific activity of 45 GBq/μmol. The labeled compound [(18)F]18 was stable in plasma and excreted by the liver and kidneys in vivo. In conclusion, the fluorosilylphenyldi-tert-butyl (SiFA) group is more stable in plasma than fluorosilyldiphenyl moiety. Thus, compound [(18)F]18 is suitable for further in vivo assessments.

Topics: Animals; Fluorine Radioisotopes; Humans; Hypoxia; Nitroimidazoles; Positron-Emission Tomography; Rats; Rats, Wistar; Silicon; Tissue Distribution

Anoxic degradation of sedimentary biogenic debris using closed incubation experiments was studied at two sampling stations in the Gulf of Trieste (northern Adriatic). Production rates of dissolved inorganic carbon (DIC), NH4+, PO(4)3- and dissolved Si (dSi), and reduction rates of SO(4)2- were measured and anoxic mineralization rates were modeled using a first order G-model and multi-G approach. The depth profiles of these rates revealed an exponential decrease indicating that the largest fraction of mineralization of biogenic debris and SO(4)2- reduction occurs in the surficial sediment layer and on the sediment surface. Comparing the depth-integrated anoxic mineralization rates at both stations with benthic fluxes of DIC, NH4+, PO(4)3- and dSi measured at the in situ temperature in the dark, it appears that the DIC and PO(4)3- fluxes are higher because the mineralization mostly occurs at the sediment-water interface, and that besides SO(4)2- reduction, other electron acceptors are involved in the organic matter decomposition pathway in these surficial sediments. The NH4+ production was higher than the benthic fluxes because of NH4+ oxidation. The production of dSi was in good agreement with benthic fluxes implying that temperature is the main factor of dSi production and benthic fluxes in these sediments.

Topics: Carbon; Environmental Monitoring; Geologic Sediments; Hypoxia; Nitrogen; Organic Chemicals; Oxidation-Reduction; Phosphorus; Quaternary Ammonium Compounds; Silicon

Hypoxic pulmonary vasoconstrictor (HPV) responses were measured with repeated intermittent hypoxic challenges in eight non-traumatized closed chest dogs anesthetized with pentobarbital. The right lung was ventilated continuously with 100% O2 while the left lung was either ventilated with 100% O2 (control) or ventilated with a gas mixture containing 3-4% O2 (hypoxia). Mean per cent left lung blood flow for all four normoxic periods was 43.1 +/- 1.5% (mean +/- SE) of the total blood flow by the SF6 excretion method and 40.8 +/- 1.1% by the differential CO2 excretion method, corrected for the Haldane effect. With hypoxic ventilation, flow diversion from the hypoxic lung was maximal with the first exposure and did not change subsequently with a total of four alternating exposures to normoxia and hypoxia. Flow diversion during hypoxia was approximately 50.5 +/- 2.4% by the SF6 method and 50.3 +/- 3.5% by the VCO2 method. This result contrasts with the increasing flow diversion response with intermittant hypoxic exposure that has been reported in animals exposed first to thoracotomy and surgical dissection. It is concluded that in the absence of surgical trauma the initial response to hypoxia is maximal and is not potentiated by repeated hypoxic stimulation.

Topics: Anesthesia, Intravenous; Animals; Dogs; Female; Fluorides; Hypoxia; Pulmonary Circulation; Respiration, Artificial; Silicic Acid; Silicon; Time Factors; Vasoconstriction