MEASUREMENTS OF OXYGEN-TENSION IN NATIVE AND TRANSPLANTED RAT PANCREATIC-ISLETS

This study was performed to measure the oxygen tension before and afte r revascularization of pancreatic islets transplanted beneath the rena l capsule and to investigate to what extent this was affected by acute and chronic hyperglycemia. In addition, the oxygen tension in islets within the pancreas was determined. Po-2 was measured with a modified Clark electrode (tip 2-6 pm o.d.). Within native pancreatic islets, th e mean Po-2 was higher (31-37 mmHg) than within the exocrine pancreas (20-23 mmHg). The mean oxygen tension in the transplanted islets the d ay after implantation was half of that recorded in native islets (14-1 9 mmHg) and did not differ between normoglycemic and diabetic recipien ts. At 1 month after transplantation, when revascularization had occur red, the mean Po-2 in the islet grafts was 9-15 mmHgf in normoglycemic animals but was lower (6-8 mmHg) in diabetic animals, whereas the blo od perfusion of the transplants, as measured with laser-Doppler flowme try (probe diameter 0.45 mm), was similar in both groups. The mean oxy gen tension in the superficial renal cortex surrounding the implanted islets was similar in all groups and remained stable at 13-21 mmHg. In travenous administration of D-glucose (1 g/kg) did not affect the oxyg en tension in any of the investigated tissues. We conclude that the me an Po-2 in islets implanted under the renal capsule is markedly lower than in native islets, not only in the immediate posttransplantation p eriod but also 1 month after implantation, i.e., when revascularizatio n has occurred. Furthermore, persistent hyperglycemia in the recipient leads to a further decrease in graft oxygen tension. To what extent t his may contribute to islet graft failure is at present unknown.