Stability of fluorescein labeled dextrans in vivo and in vitro.

Fluorescein thiocarbamoyl dextrans (FITC-dextrans) were studied with respect to their potential use as tracer substances in circulatory research. It was found that the preparations did not contain any detectable free fluorescein. FITC-dextrans could conveniently be determined by fluorometry in the concentration range of 0.05–30 μg/ml. Gel filtration experiments demonstrated that the fluorescein label was evenly distributed in the molecular weight range of the dextran molecules, and the carbamoyl-dextran linkage was found to be perfectly stable both in in vitro and in vivo conditions. Intravenous infusion of FITC-dextran into rabbits resulted in plasma disappearance curves similar to those obtained with corresponding unlabeled dextran preparations. Consequently, FITC-dextrans should prove valuable as tracers for the study of many aspects of circulation.