Secretion of insulin-like growth factor-II into bile of rats of different ages

Bile from rats of different ages (suckling 10-12 days; weanling 30-33 days, and adult 60-70 days) was collected and studied for the presence of immuno - and receptor-assayable insulin-like growth factor-II (IGF-II) concentrati ons. Concentrations of RIA IGF-II in bile were highest in suckling rats (23 0 +/- 38 ng/ml) and lowest in adults (47 +/- 7 ng/ml). These concentrations were approximately twice those of the bile IGF-I concentration in suckling s, as measured in a previous study. Selected bile samples were also assayed using a competitive binding assay with a crude preparation of adult rat li ver membranes bearing the IGF-II receptor. These studies confirmed the pres ence of receptor- (as well as immuno-) active IGF-II in bile. Since bile fl ow rates increased dramatically after the suckling period, bile delivery ra tes of IGF-II were normalized as picograms per gram body weight per hour. W hen such calculations were done, bile IGF-II delivery rates to the small in testine were highest in sucklings and weanlings in comparison to adult rats . Thus non-enterically derived (milk- and bile-borne) IGF-II delivery to th e suckling small intestine can be approximated at roughly 1 mu g/day. Unlik e IGF-I, intravenously injected IGF-II could not be detected in suckling bi le, suggesting a predominantly hepatic origin. From this study we conclude that there exists a significant delivery of receptor-active IGF-II to the g astrointestinal tract of rats of all ages. Copyright (C) 2000 S. Karger AG, Basel.