Islet transplantation in diabetic Lewis rats--a comparison of the transplantation sites kidney and spleen capsule.

Animal studies have been used to investigate different transplantation (Tx) sites to find best conditions for Tx in humans. A few long-term experiments of comparisons of different Tx-sites have been published. Therefore the aim of our study was to compare islet grafts transplanted under the kidney capsule (KTx) of male Lewis rats with grafts transplanted under the spleen capsule (STx) and to observe these animals over a period of 6 months. Diabetes was induced by Streptozotocin and rats were each transplanted with 2000 syngeneic islets under the kidney respectively the spleen capsule. 2 weeks after Tx all animals were normoglycemic. Over the following 6 months nearly normal plasma glucose levels could be maintained in the KTx group whereas the STx animals already became diabetic after 3 months. An oral glucose load after 2 months showed slightly elevated plasma glucose levels in the KTx group which only gained statistical significance in a similar test after 6 months. In the STx group definitely impaired glucose tolerance already prevailed at 2 months. An i.v. glucose tolerance test performed 6 months after Tx showed a loss of first phase insulin release in both Tx groups but an increased second phase release and a preserved response to L-arginine compared to controls. Insulin content remained unchanged in the KTx group, but was markedly reduced in the STx group after 6 months. In conclusion we may say that KTx is able to establish near-normoglycemia in streptozotocin-diabetic Lewis rats which can be maintained over a long period of time despite abnormal glucose tolerance and impaired insulin secretion STx could normalize plasma glucose only up to 3 months showing early impairment of glucose and insulin regulation. If KTx has immunological or local advantages (islet vascularization, innervation) compared to STx with higher dispersion of islets in spleen and portal vascular system remains unclear.