In‐vivo analysis of angiogenesis and revascularization of transplanted pancreatic islets using confocal microscopy

A technique to measure angiogenesis and revascularization in pancreatic islets transplanted at the renal subcapsular site in the rat has been developed. In‐vivo imaging of the microcirculation of transplanted pancreatic islets was conducted using a confocal scanning laser microscope (CSLM) to achieve optical sectioning through the graft in order to perform a computer reconstruction of the three‐dimensional neovascular morphology. Individual islets were harvested by enzymatic digestion of excised pancreas from Fischer 344 rats. Isolated islets were cultured for 24 h, and approximately 300–350 islets were transplanted at the renal subcapsular site of the left kidney in an anaesthetized rat. Six to 14 days post‐transplantation, the animal was anaesthetized and prepared for in‐vivo imaging of the microvasculature on a Zeiss LSM‐10. Optical contrast of the microvasculature was enhanced by the administration of fluorescein‐labelled dextran into the circulating blood. The transplant site was identified and serial sections were obtained through the vascular bed at varying z‐intervals. Complementary fluorescence video images were also obtained via a silicon intensifier tube camera mounted on the CSLM. At completion of the imaging procedure, the kidney was returned into the body cavity, the area was sutured and the animal was allowed to recuperate for subsequent examinations. Image processing algorithms, such as grey‐level thresholding, median filtering, skeletonization and template matching, were applied to compute the vessel density and diameters and extrapolated to measure 3‐D vessel lengths and the tortousity index of the neovasculature.