Syngeneic fetal rat islets were isolated and transplanted into alloxan-diabetic inbred male Lewis rats. The effect of transplantation of islets into the cerebral ventricles on the diabetic state of the recipients was compared with that of the conventional transplantation of islets homeotypically into the liver via the portal vein. Fourteen of fourteen rats surviving after stereo-taxic implantation of islets into the ventricles returned to normoglycemia; normoglycemia has been maintained for up to 34 wk. Glucose tolerance tests revealed an improved, although not completely normalized, pattern. Histologie examination of the brains of these recipients revealed clusters of intact islets in the ventricle. These data provided a physiologic basis for further investigation of the immunologically privileged nature of the intraventricular space as a site for implantation of allogeneic pancreatic islets. Islets from Wistar-Furth rats (major histocompatibility difference) or Fischer 344 rats (minor histocompatibility difference) were transplanted into the ventricles of alloxan-diabetic Lewis rats. There were only small and unsus-tained changes in body weight and blood and urine glucose of any of the rats receiving the allogeneic islets. Histologie examination of the ventricles of these rats 3 wk after transplantation revealed only glial scar tissue. These data suggest that the cerebral ventricles cannot serve as a privileged site for islet transplantation, at least using the type of islet preparation employed in these experiments.

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