Fluosol 43 intravascular persistence in mice measured by 19F nmr

Quantitative determination of the intravascular persistence of F-tri-n-butylamine (FC 43 as Fluosol 43) in mice was carried out using 19F nmr spectroscopy. The method allows the direct study of whole blood, neither separation nor extraction of the sample being required. Accuracy (reproducibility) is better than +/- 3%, and is comparable to that of the gas chromatographic (gc) method. The sensitivity of detection is less than that of the gc method but is sufficient for this biological study. It was observed that the intravascular elimination of F-tri-n-butylamine follows a non-linear kinetic and becomes faster about 40 h after the injection. This phenomenon may be explained by the size-increase of the FC 43 droplets in the emulsion. Indeed, at about 40 h after injection, the level of Pluronic F-68 in the bloodstream was no longer sufficient to maintain the stability of the FC-43 droplets. They therefore tended to coalesce forming larger droplets that were phagocytosed more rapidly by the histiocytes of the reticuloendothelial system.