ORIENTATION OF MICROVASCULAR BLOOD-FLOW IN PANCREATIC-ISLET ISOGRAFTS

There is evidence that intraislet cellular communication and hormone d elivery within the islets of Langerhans is controlled via capillary pe rfusion directed from the B cell core to the A/D cell mantle (intraisl et portal system). To determine whether vascularization of freely tran splanted islets repeats this ''coreto-mantle'' capillary perfusion, ha mster islets were isolated by collagenase digestion and transplanted i nto a skinfold chamber of syngeneic animals (n = 12). 14 d after trans plantation, the microvasculature of the islet grafts was analyzed by i n vivo fluorescence microscopy. The capillary glomerulum-like network of the islet grafts (n = 109) was found supplied by individual arterio les, which regularly pierced the islet and broke into capillaries with in the graft (96/109 [88.1%]), resulting in capillary flow directed fr om the core to the islet's periphery. Only in 13 of 109 islets (11.9%) arterioles broke into capillaries at the outside margin of the islet and capillary flow was directed simultaneously to vessels located with in the core, as well as the periphery of the graft. The islet's capill ary network was drained by individual venules and intercapillary anast omoses between the newly formed islet capillaries and the preexisting capillaries of the host muscle tissue. Immunohistochemical staining re vealed B cells located within the core, and A and D cells scattered in the periphery of the islets, indicating reestablishment of sequential B --> A/D cellular perfusion of the grafts. Thus, freely transplanted islets develop an intra-islet portal system, similarly to that of pan creatic islets in situ.