Chronically decreased oxygen tension in rat pancreatic islets transplanted under the kidney capsule

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.

The partial pressure of oxygen was measured in pancreatic islets transplanted beneath the renal capsule of diabetic and nondiabetic recipient rats with a modified Clark electrode (outer tip diameter 2-6 microm). The size of the graft (250 islets) was by purpose not large enough to cure the diabetic recipients. The oxygen tension in islets within the pancreas was also recorded. Blood perfusion was measured with the laser-Doppler technique.

Within native pancreatic islets, the partial pressure of oxygen was approximately 40 mm Hg (n=8). In islets transplanted to nondiabetic animals, the oxygen tension was approximately 6-7 mm Hg 1, 2, and 9 months posttransplantation. No differences could be seen between the different time points after transplantation. In the diabetic recipients, an even more pronounced 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 (approximately 15 mm Hg). Intravenous administration of glucose (0.1 gxkg(-1)x min(-1)) did not affect the oxygen tension in any of the investigated tissues. The islet graft blood flow was similar in all groups, measuring approximately 50% of the blood flow in the kidney cortex.

The oxygen tension in islets implanted beneath the kidney capsule is markedly lower than in native islets up to 9 months after transplantation. Moreover, persistent hyperglycemia in the recipient causes an even further decrease in graft oxygen tension, despite similar blood perfusion. To what extent this may contribute to islet graft failure remains to be determined.