Syngeneic transplantation of fetal rat pancreas. II. Effect of insulin treatment on the growth and differentiation of pancreatic implants fifteen days after transplantation.

Eight 18-days-postcoitum fetal pancreases were transplanted to isogenic alloxan-diabetic male rats. Some recipients were treated with insulin for seven days immediately after transplantation. Eight animals in both the insulin-treated group and control group were killed 15days after transplantation for morphologic and hormonal studies of the transplanted tissue. Using the morphometric technique of linear scanning, the insulin, glucagon, and somatostatin immunocytochemically positive, cell masses of the fetal pancreatic implants were quantitated. The beta cell mass of the implants from the control animals increased roughly eightfold from the time of transplant; insulin treatment resulted in a further two- to threefold increase. The insulin content of the implants increased more than did the beta cell mass, resulting in the fivefold increase in insulin per beta cell. The alpha cell and delta cell masses did not change during the transplant site, the mass of functional beta cells, and the cell-to-cell content of the implanted tissue. These results are discussed in relation to previous quantitative studies of pancreatic islet cell growth. The relationships of the transplant site, the mass of functional beta cell, and the cell-to-cell interaction within the islet to the maintenance of glucose homeostasis are also discussed.