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The testis has been suggested as an immune privileged site for islet transplantation. The present study evaluated this hypothesis by transplanting islets from Wistar Furth rats into (a) the testes; (b) the subcapsular space of the kidneys; or (c) the cryptorchid abdominal testes of streptozotocin-induced diabetic Swiss ND4 mice. Transplantation of 800 rat islets into the cryptorchid testes normalized blood glucose for 9.3 +/- 1.4 (Mean +/- SD) days, not significantly different from that of the scrotal testis site (12.4 +/- 1.3), or when the subcapsular space of the kidneys was used (11.5 +/- 1.2). When mouse islets were isotransplanted into the cryptorchid testes of diabetic mice, normoglycemia was maintained for the entire 3 month study period. Histologic examination of the islet xenograft-bearing cryptorchid testes at day 7 post transplantation and 2 days after returning to hyperglycemia revealed lymphocyte infiltration surrounding and inside the graft. No lymphocyte infiltration was seen in the isograft bearing-testes at 3 mo after transplantation. Cyclosporine A (CsA, 15 mg/kg/day) administration to the islet xenograft recipient slightly prolonged the normoglycemic period to 13.7 +/- 1.8 days (p < 0.01). Increasing CsA dose to 25 mg/kg induced a 66% (4/6) mortality, and did not further prolong the normoglycemic period. Using a lower number of rat islets (200 or 400 islets), prolonged graft survival was achieved in some (4 out of 20) animals when the cryptorchid testis was used. In contrast, transplantation of 400 rat islets into the subcapsular space of the kidneys was not associated with prolonged graft survival.(ABSTRACT TRUNCATED AT 250 WORDS)

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This study tested the hypothesis that normalization of glucose homeostasis after islet transplantation is correlated to the number of islets, and by increasing this number a complete normalization of glucose homeostasis could be achieved, 1,200 or 2,400 islets were transplanted into the left kidney subcapsular space in streptozotocin-induced diabetic rats. Intravenous glucose tolerance tests were performed at 10 days, 3 and 6 months after transplantation. Transplantation of both 1,200 and 2,400 islets normalized the basal blood glucose levels within 24-48 hours, which remained normal for the entire study period of 6 months. Basal plasma insulin levels and body weight were also normalized in both transplanted groups. Transplantation of 2,400 islets achieved normal glucose-induced insulin secretion at 10 days after transplantation and for the following 6 months. In contrast, glucose intolerance was present in rats transplanted with only 1,200 islets. It is concluded that complete glucose homeostasis after islet transplantation is dependent on the number of transplanted islets and can be achieved by increasing this number.