EFFECT OF MICROENCAPSULATION ON OXYGEN DISTRIBUTION IN ISLETS ORGANS

In islet transplantation, limitation of oxygen supply may restrict gra ft function, particularly when encapsulated tissue is used. Therefore, oxygen tensions (PO2) in isolated islet organs (Brockmann bodies) of Osphronemus gorami were measured. In a thermostatically (37 degrees C) controlled measuring chamber, PO2 values were recorded at subsequent microelectrode positions on a radial track toward the center of the or gan. In 2 independent groups, we studied the effect of fluid convectio n (n=12) and microencapsulation (n=12). In both groups, sigmoidal PO2 profiles were found, which permit differentiation in an oxygen deplete d zone surrounding the surface, a steep decline inside the tissue corr esponding to the oxygen-consuming rim, and a plateau in the center wit hout oxygen consumption which reflects necrosis. The PO2 values decrea sed (P<0.001) when convection was stopped. Compared with starting valu es, PO2 levels at the surface were 61+/-3% with and 41+/-4% without co nvection. Surface values for encapsulated tissue were 44+/-5% compared with 64+/-4% in nonencapsulated tissue. In the tissue, center oxygen dropped to 27+/-5% with convection and to 6+/-3% without, and to 11+/- 3% for encapsulated tissue compared with 22+/-4% for nonencapsulated t issue. The thickness of the outer oxygen-depleted zone was 81+/-16 mu m with and 196+/-57 mu m without convection (P<0.001), and 188+/-16 mu m for encapsulated and 94+/-14 mu m for nonencapsulated tissue (P<0.0 01). The oxygen-consuming rim was 295+/-22 mu m with and 235+/-36 mu m without convection (NS), and 216+/-15 mu m for encapsulated and 315+/ -24 mu m for nonencapsulated tissue (P<0.01). These results illustrate the special distribution of oxygen in isolated islet tissue and indic ate that barium alginate encapsulation may worsen oxygenation mainly b y expanding the ''unstirred water layer'' surrounding the tissue.