Effects of insulin-like growth factor I (IGF-I) on the small intestine: A comparison between oral and subcutaneous administration in the weaned rat

Several studies have suggested that growth factors play an important role in the development and the maintenance of the gastrointestinal tract, Colostrum and normal breast milk as well as intestinal secretion are reported to contain IGF-I, Thus, the objective of this study was to investigate whether the route of administration of IGF-I, subcutaneously and orally, was important for the may of influencing the gastrointestinal tract in the weaned rat and further to observe if this effect was affected by different feed regimens. Well nourished weaned rats subcutaneously administered IGF-I (2 mg/kg body weight and day during 14 days) were found to have significantly increased relative weights of the small intestine, increased duodenal crypt depths and villi heights compared with control rats, The same dose given orally in bovine milk had no effect, Furthermore, a study was performed with the same dose of IGF-I given for 7 days together with a restricted feed regimen, Similar observations; although of a slightly smaller magnitude, were found, These observations indicate that the effect of IGF-I on gastrointestinal renewal in the weaned rat is not depending on an IGF-I supply through the gastrointestinal fluids but rather through a supply via the circulation or by a local intestinal production,The effects were statistically significant both in well fed and malnourished conditions.