Immunocytochemical study of pancreatic islet revascularization in islet isograft. Effect of hyperglycemia of the recipient and of in vitro culture of islets.

We studied the revascularization process of isogeneic islets grafted into the kidney subcapsular space of streptozotocin-induced diabetic and nondiabetic rats by a double-labeling, indirect immunofluorescence technique using a rabbit antiserum to human factor VIII-related antigen (which identifies endothelial cells) and a guinea pig anti-insulin antiserum (which labels pancreatic beta cells). Freshly isolated islets contained a network of capillary endothelial cells, whereas 1-week-cultured islets at 37 degrees C have completely lost their intra-islet endothelial cells. Overnight cultured islets contained only occasional endothelial cells. When these islets were grafted under the kidney capsule of nondiabetic rats, they rapidly acquired a new endothelial cell lining as demonstrated by the positivity of staining for factor VIII-related antigen at day 5 after implantation. On the other hand, 1-week-cultured islets failed to become fully revascularized until day 7 after transplantation. Streptozotocin-induced diabetic rats grafted with 1000 islets normalized their blood glucose values (< 11 mM/L) 2-4 weeks after implantation, whereas transplantation of 2500-3000 islets resulted in normoglycemia after 4.7 +/- 2 days (mean +/- SD). Nevertheless, hyperglycemia of the recipient did not adversely affect the process of revascularization of islet isografts which initiated at day 3 and was almost completed by day 5 after implantation.