Changes in the molecular composition of circulating hydroxyethyl starch.

1. Hydroxyethyl starch (HES) of molecular weight 450,000 has been extensively investigated as a plasma volume expander and HES of molecular weight 60,000 has been proposed for use as a cryoprotective agent in the freezing for preservation of red blood cells. In these applications considerable amounts of HES may be injected intravenously and it is therefore desirable to understand its behaviour in vivo.2. After intravenous injection into rabbits, plasma levels of HES and clinical dextrans were determined using anthrone. HES persisted longer in the circulation than did the dextrans.3. HES was recovered from the bloodstream of rabbits and shown by gel filtration to be of a narrower molecular size distribution than the injected material. Smaller molecules were removed, presumably by filtration at the glomerulus. Larger molecules may have been removed by cells of the reticuloendothelial system or possibly through the action of amylase.4. The amylase in saliva was shown to break down HES into molecules of intermediate size with very little production of maltose units.