An investigation into the value of hydroxyethyl starch as a cryoprotectant for purified human and rat islets of langerhans.

The purpose of the work described in this thesis was to determine whether hydroxyethyl starch (HES) could be used either alone or in combination with dimethyl sulphoxide (DMSO) for the cryoprotection of purified human and rat islets of Langerhans. The introduction to this thesis comprises two parts. Chapter 2 discusses the pathophysiology of diabetes mellitus and its present day treatment by both conventional means and the transplantation of insulin-producing tissue is reviewed. Chapter 3 discusses the theoretical basis of cryobiology and the application of cryopreservation to the transplantation of purified islets is reviewed. There follows an account of the probable mechanism of cryoprotection provided by HES and a description of the method by which the theoretical minimum concentration of HES required to cryoprotect islets can be calculated. Five experimental chapters are then presented. The first describes the techniques used to isolate human and rat islets. The next experimental chapter describes the development of a microfluo- rometric viability assay for isolated human and rat islets. The third experimental chapter describes experiments to determine the cause of slow-freezing injury to human and rat islets and thereafter the theoretical minimum concentration of HES required for the cryoprotection of islets is calculated. In the next chapter the results of freezing bath experiments to examine the cryoprotective properties of the 3 types of HES currently available are presented. Islets were frozen at -10°C and thawed either rapidly or slowly and their viability measured. A further section of this chapter is concerned with the cryoprotectant properties of HES in combination with DMSO. The final experimental chapter examines the cryoprotective properties of HES/DMSO combinations for islets frozen at -10°C and then cooled to -196°C. In the final chapter the experimental results are reviewed and possible avenues of further investigation are discussed.