Localized magnetic resonance spectroscopy measurement of brain lactate during intravenous lactate infusion in healthy volunteers.

Proton magnetic resonance spectroscopy (1H MRS) localized to the left temporal-parietal region in 8 healthy volunteers detected a 2.1-fold +/- 0.7-fold increase (all values +/-SD) in brain lactate during intravenous infusion of 0.5 molar (M) sodium lactate (5 meq/kg over 20 minutes). Significant increases in brain lactate occurred within 5-10 minutes after starting lactate infusion, progressively rose during the infusion, then decreased towards baseline levels during 30 minutes post-infusion. Venous lactate concentration increased from 0.8 +/- 0.2 mM to 10.9 +/- 4.1 mM or 13.6-fold during the infusion. Flow phantom findings in vitro suggest attenuation of 1H MRS blood lactate signal from arteries and veins as a result of flow velocity effects. Correlations between paired blood and brain lactate measurements at each sampling time indicate a non-linear relationship between compartments during lactate infusion.     

Influence of adsorption time, rocking, and soluble proteins on the plaque assay of monodispersed poliovirus

Factors that could affect adsorption of monodispersed poliovirus to cell culture monolayers were evaluated. These included varying the virus adsorption period under static and nonstatic (rocked) conditions and altering the rocking rate. The effects of several soluble proteins on plaque formation, enumeration, and size were also evaluated. Rocking involved the mechanical spread of viruses over cell culture monolayers for 1 to 4 h. Rocked cultures exhibited significantly higher (P less than 0.05) plaque counts than corresponding static cultures. Optimal plaque counts were obtained after a 2-h adsorption period with rocking; increasing the period to 4 h did not significantly increase PFU. Optimal counts were not obtained until greater than or equal to 4 h with static adsorption. Plaque counts were not affected by increasing the rocking rate above one oscillation per minute, but a slower rocking rate resulted in a significant decrease in plaques. Adsorption of poliovirus in the presence of 3% solutions of beef and meat extracts, acid-precipitated oyster protein, two brands of skim milk, and 3 and 10% fetal bovine serum was compared with adsorption in protein-free controls. Significant reductions (P less than 0.05) in plaque counts occurred with one brand of skim milk, whereas 3% beef extract yielded highly significant reductions (P less than 0.01) in plaque counts and appreciable decreases in plaque sizes. Salinities of protein-containing virus inocula were high for beef and meat extracts but somewhat below physiological levels for the remaining inocula. Beef extract-associated reductions in PFU were eliminated after the extracts were dialyzed. Plaque reductions were associated with dialyzable components of the beef extract but not with the inoculum salinity.     

Mechanism of action of adenosylcobalamin: 3-fluoro-1,2-propranediol as substrate for propanediol dehydrase--mechanistic implications.

3-Fluro-1,2-propanediol has been found to be a substrate for propanediol dehydrase and has very similar binding and catalytic constants compared to the natural substrate. The only isolable products of the reaction are acrolein and inorganic fluoride; with 3-fluoro-3,3-dideuterio-1,2-propanediol as substrate, only 3,3-dideuterioacrolein is obtained. These results indicate that the primary product of the reaction is 3-fluoropropionaldehyde which spontaneously loses hydrogen fluoride to yield acrolein. The similar kinetic parameters for the fluorinated as compared to the normal substrate suggest that significant charge does not develop on the fluorinated or, by implication, the natural substrate during any rate-limiting steps of the reaction. These results support a radical, as contrasted to an ionic pathway for reactions involving adenosylcobalamin and diol dehydrase.