Ingestion of fluorescein-labeled hydroxyethyl starch by organ-bound and circulating cells of the reticuloendothelial system

Background: Intravenously administered hydroxyethyl starch (HES) is ingeste d and stored by organ-bound cells of the reticuloendothelial system (RES). Aim of the present study was to examine the transport mechanisms for HES be tween these organs of the RES. Material and Methods: Male Wistar rats were infused with 1 mi of a 1% fluorescein-labeled HES (FITC-HES). Before FITC-H ES infusion, lymphocyte, granulocyte and monocyte clusters were identified by now cytometry. Prior to as well as 180 and 360 min after FITC-HES infusi on, blood samples were collected and cell-bound fluorescence was examined b y now cytometry. For histochemical examinations, animals which had received the same FITC-HES infusion were sacrificed 180 and 360 min after infusion. Results: The infusion of FITC-HES increased the cell-bound fluorescence exp ression in peripheral blood. The highest fluorescence intensities could be located in the monocyte cluster of 1:he cytograms. Most of the cells with l ower increases of fluorescence expression were polymorphonuclear granulocyt es. In the lymphocyte cluster the fluorescence did not change. Splenic fluo rescence appeared in the marginal-zone macrophages, where circular structur es with high fluorescence intensities could be recognized. Additionally, we found intracellular fluorescence vesicles in Kupffer cells. Conclusions: The commonly suggested mechanism of the tissue storage of HES is a direct uptake of the intravascularly persisting colloid by sessile cel ls of the RES. The existence of clusters of circulating cells expressing si gnificantly increased fluorescence intensities after infusion of a fluoresc ence-labeled HES indicates that a further cellular transport system does ex ist for HES.