Markedly decreased oxygen tension in transplanted rat pancreatic islets irrespective of the implantation site

In this study, we syngeneically transplanted islets to three different impl antation sites of diabetic and nondiabetic rats, then 9-12 weeks later we m easured the blood perfusion and compared the tissue partial pressure of oxy gen (Po-2) levels of these transplanted islets to endogenous islets. Modifi ed Clark microelectrodes (outer tip diameter 2-6 mum) were used for the oxy gen tension measurements, and islet transplant blood perfusion was recorded by laser-Doppler flowmetry (probe diameter 0.45 mm). The islet graft blood perfusion was similar in all islet grafts, irrespective of the implantatio n site. In comparison, the three implantation organs (the kidney cortex, li ver, and spleen) differed markedly in their blood perfusion. There were no differences in islet graft blood perfusion between diabetic rand nondiabeti c recipients. Within native pancreatic islets, the mean Po-2 was similar to 40 mmHg; however, all transplanted islets had a mean Po-2 of similar to5 m mHg. The oxygen tension of the grafts did not differ among the implantation sites. In diabetic recipients, an even lower Po-2 level was recorded in th e islet transplants. We conclude that the choice of implantation site seems less important than intrinsic properties of the transplanted islets with r egard to the degree of revascularization and concomitant blood perfusion. F urthermore, the mean Po-2 level in islets implanted to the kidney, liver, a nd spleen was markedly decreased at all three implantation sites when compa red with native islets, especially in diabetic recipients. These results ar e suggestive of an insufficient oxygenization of revascularized transplante d islets, irrespective of the implantation site.