Chronically decreased oxygen tension in rat pancreatic islets transplantedunder the kidney capsule

Background A factor of potential importance in the failure of islet grafts is poor or inadequate engraftment of the islets in the implantation organ. This study measured the: oxygen tension and blood perfusion in 1-, 2-, and 9-month-old islet grafts. Methods. The partial pressure of oxygen was measured in pancreatic islets t ransplanted beneath the renal capsule of diabetic and nondiabetic recipient rats with a modified Clark electrode (outer tip diameter 2-6 mu m) The siz e of the graft (250 islets) was by purpose not large enough to cure the dia betic recipients. The oxygen tension, in islets within the pancreas was als o recorded. Blood perfusion was measured with the laser-Doppler technique. Results. Within native pancreatic islets, the partial pressure of oxygen wa s approximate to 40 mm Hg (n=8), In islets transplanted to nondiabetic anim als, the oxygen tension was approximate to 6-7 mm Hg 1, 2, and 9 months pos ttransplantation. No differences could be seen between the different time p oints after transplantation. In the diabetic recipients, an even more prono unced decrease in graft tissue oxygen tension was recorded. The mean oxygen tension in the superficial renal cortex surrounding the implanted, islets was similar in all groups (approximate to 15 mm Hg), Intravenous administra tion of glucose (0.1 g x kg(-1) x min(-1)) did not affect the oxygen tensio n in any of the investigated tissues. The islet graft blood now was similar in all groups, measuring similar to 50% of the blood flow in the kidney co rtex. Conclusion. The oxygen tension in islets implanted beneath the kidney capsu le is markedly lower than in native islets up to 9 months after transplanta tion. Moreover, persistent hyperglycemia in the recipient causes an even fu rther decrease in graft oxygen tension, despite similar blood perfusion. To what extent this may contribute to islet graft failure remains to be deter mined.