The effect of total parenteral nutrition (TPN) on the enteroinsular axis in the rat.

The effect of 6 days of total parenteral nutrition (TPN) on the enteroinsular axis was studied in vivo and in vitro in the rat. During the TPN period, blood samples were taken from control and TPN animals to determine the comparative pattern of GIP release. Glucose, insulin and GIP responses to oral glucose (OGTT) were compared in TPN 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 TPN altered the sensitivity of the beta cell. In conjunction with these studies the number and distribution of GIP-containing cells were compared in control and TPN animals. TPN resulted in no change in basal levels of glucose, insulin and IR-GIP. An exaggerated insulin response to OGTT occurred after TPN whereas the glucose response was reduced. The IR-GIP response to glucose was normal following TPN. The isolated perfused pancreas showed a 30% increase in insulin release in response to GIP after TPN. The insulin response to glucose appeared normal as did the number and distribution of GIP cells. Fluctuations in GIP and insulin levels in control animals were diurnal in nature, whereas IR-GIP levels in TPN animals remained near fasting levels. It was hypothesized that the increase in beta cell sensitivity to GIP may be causally connected to the exposure of the pancreas to chronically low levels of GIP during TPN.