Insulin Secretion by Rat Islet Isografts of a Defined Endocrine Volume After Transplantation to Three Different Sites

We have analysed the graft function of rat islet isografts of identical and well-defined endocrine volumes after transplantation to three different sites (kidney, liver and spleen). Graft endocrine mass was determined by measuring the total islet volume prior to transplantation and was chosen to be similar to the endocrine volume in the normal adult rat pancreas. Graft function was tested in unanaesthetized, unstressed rats by the responses to glucose infusion and to a meal. All transplanted animals returned to normoglycaemia within one week after transplantation. At one month, basal glucose and insulin levels were similar to controls in rats with grafts to the spleen, but higher in rats with grafts to the kidney or liver. Irrespective of the transplantation site, recipients had higher glucose and lower insulin levels than controls in response to glucose infusion, but in response to a meal these differences from normal were less obvious. Finally, recipients showed both an acute insulin response to glucose infusion as well as a pre-absorptive insulin release after food ingestion, irrespective of the transplantation site. Our findings indicate that the insulin response to glucose infusion and to a meal is quantitatively reduced, but qualitatively intact after transplantation to the kidney, liver or spleen.