Islet transplantation and glucose regulation.

Transplantation of isolated islets of Langerhans for treatment of diabetes has been developed through experimental research in several species and is now being applied to humans with some success albeit limited. A significant problem for human islet allotransplantation or autotransplantation (following pancreatectomy) is the relatively poor yield of islets available for transplantation. The metabolic function of islet transplant recipients that have achieved insulin independence reflects the relatively small mass of insulin-secreting tissue implanted and the fact that only the intraportal site of transplantation appears to allow sufficient graft function to achieve insulin independence. The long-term function of such grafts has been poor, with most grafts showing deterioration in function within 5 years. Studies of islet transplantation in other species showed a similar result, although other sites for islet graft implantation, such as the spleen or kidney capsule, may be associated with a better outcome. These studies, however, also suffer from problems of relatively limited islet mass. Only in the rodent model where isogeneic strains are available is it possible to transplant sufficient numbers of islets to obtain an equivalent functional islet mass similar to that found in the normal pancreas; and in this case near-normal glucose metabolism is obtained and is maintained for the life-span of the animal.