Effect of jejunoileal bypass in the rat on the enteroinsular axis.

The effect of jejunoileal bypass (JIB) on the enteroinsular axis was studied in vivo and in vitro in the rat. Glucose, insulin and GIP responses to oral glucose were compared in JIB and control rats. The effect of glucose and GIP on insulin release from the isolated perfused pancreas of the same animals was investigated to determine if JIB altered the sensitivity of the beta cell. Immunocytochemical studies of gut and pancreas were also carried out. Glucose, insulin and GIP responses to a glucose load were blunted after JIB, although basal GIP levels were elevated in these animals. The insulin response of the perfused JIB pancreas to GIP was 70% reduced from controls although the insulin response to glucose appeared normal. The size and area of JIB islets were unchanged from controls as was the distribution of insulin, glucagon, somatostatin and pancreatic polypeptide. GIP immunoreactive cells were present in all regions of the intestine including the JIB blind loop. This study confirms the findings of others that a relationship exists between reduced GIP and insulin response to oral glucose after JIB, and indicates that a decrease in sensitivity of the beta cell to GIP occurs following JIB that is not rapidly reversible. GIP secreted from blind loop mucosa may contribute to the high basal GIP found in JIB rats and may be causally connected to the fall in beta cell sensitivity.