Double-labelled methyl-14C,5-3HCDPcholine has been synthesized and subjected to a pharmacokinetic analysis in several biological systems. In transport experiments with intact human erythrocytes no ...incorporation of radioactivity is observable. On the other hand the results obtained with perfused rat liver suggest a rapid cleavage of the pyrophosphate bridge of the molecule, followed by a rapid uptake of the hydrolytic products. The plasma half-lives of intravenously injected CDPcholine and of its metabolites have been evaluated within 60 sec range. Renal and fecal excretion of the injected radioactivity is negligible: only 2.5% of administered 14C- and 6.5% of the 3H- is excreted up to 48 hr after administration. Liver and kidney are the major CDPcholine metabolizing organs, characterized by a fast and extensive uptake of choline metabolites, followed by a slow release; conversely the rate of uptake of both 3H and 14C-labelled moieties by rat brain is significantly slower, reaching a steady-state level after 10 hr. The characterization of the labelled compounds detectable in the investigated organs provides some insights on the metabolism of the drug: the 3H-cytidine moiety in all the examined organs appears to be incorporated into the nucleic acid fraction via the cytidine nucleotide pool; the 14Ccholine moiety of the molecule is in part converted, at the mitochondrial level, into betaine which accounts for about 60% of the total 14C-radioactivity associated with liver and kidney 30 min after administration; 14Cbetaine in turn acts as methyl donor to homocysteine yielding 14Cmethionine subsequently incorporated into proteins; the time dependent increase in labelled phospholipids is indicative of a recycling of the choline methyl-groups in this lipid fraction via CDPcholine and/or S-adenosylmethionine; the rather extensive amount of labelled methionine detectable in brain probably arises from its uptake from the blood stream, since the enzyme catalyzing the conversion of betaine into methionine is lacking in brain.
In order to elucidate the reaction mechanism and the substrate-binding sites, CDPcholine:1,2-diacylglycerol cholinephosphotransferase (EC 2.7.8.2), prepared from rat liver microsomal fraction, has ...been subjected to kinetic analysis and substrate specificity studies. Kinetic evidence supports the hypothesis of a Bi-Bi sequential mechanism, involving a direct nucleophilic attack of diacylglycerol on CDPcholine during the reaction. To investigate the substrate requirements for recognition and catalysis, several CDPcholine analogs, modified in the nitrogen base or in the sugar or in the pyrophosphate bridge, have been synthesized, characterized and assayed as substrates and/or inhibitors of the reaction. The amino group on the pyrimidine ring, the 2'-alcoholic function of the ribose moiety as well as the pyrophosphate bridge have been identified as critical sites for enzyme-substrates interactions.
Objective: To determine the accuracy of an enzymatic assay of serum to measure blood ethanol levels in the emergency department. Methods: A blinded, prospective study of emergency department patients ...for whom a blood ethanol was ordered and performed. After skin prep with betadine, two blood samples were drawn into separate sodium fluoride-containing vacutainers. One sample was sent to the hospital laboratory for blood ethanol analysis. The other was centrifuged for 5 minutes and the serum was then assayed using the QED A350′ Saliva Alcohol Test. Values were then compared by kappa statistic and Pearson's correlation. Sensitivity and specificity calculations were determined for the QED device to detect a blood ethanol > 100 mg dL. Results: Sixty-six patients were enrolled. The kappa value for QED compared to lab blood ethanol was 0.93. The Pearson's correlation coefficient was 0.94. The QED, in general, tended to overestimate blood ethanol slightly. The QED was 100% sensitive and 82% specific in detecting a blood ethanol > 100 mg dL. Conclusions: Analysis of serum using a QED A350′ is a sensitive and accurate index of low to moderate increases in blood ethanol appropriate to emergency department, but not legal, interpretation.
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