LUMINAL PROCESSING OF EPIDERMAL GROWTH-FACTOR IN MOUSE GASTROINTESTINAL-TRACT IN-VIVO

To test the stability of epidermal growth factor (EGF) in the gastrointestinal lumen 125I-labeled EGF was administered to the lumen of isolated stomach, duodenum, jejunum, midjejunum, and ileum of anesthetized mice (14-day-old neonatals and 8-week-old adults). Radioactivity extracted from luminal contents and tissues of gastrointestinal segments was analyzed by binding to C18 isolation cartridges followed by reversed-phase high performance liquid chromatography (RP-HPLC). At 10 min, 74-97% of administered radioactivity was present in the isolated segments (luminal contents + segment tissue). Major portions (60-88%) of radioactivity recovered from luminal contents and segment tissues bound to C18 cartridges, except for lower values (40-54%) recorded in segment tissues of adult mice. RP-HPLC identified > 90% of C18-extracted radioactivity from gastric luminal contents of neonatal and adult mice as intact [125I]EGF (30-min retention time). In adult mice, 46-51% of radioactivity extracted from midjejunal luminal contents was identified as intact [125I]EGF, whereas only 3-5% was intact [125I]EGF in neonatal mice. On the contrary, in extracts of duodenal, jejunal, and ileal luminal contents, 14-30% of radioactivity was intact [125I]EGF in neonatal mice, whereas < 3% was intact [125I]EGF in adult mice. Considerable amounts of intact [125I]EGF were present in the adult mouse gastric tissue and neonatal mouse gastric and duodenal tissues. The remainder of C18-extracted radioactivity from different luminal contents and segment tissues eluted as three major C-terminally truncated EGF derivatives. These three [125I]EGF derivatives, eluted with retention times of 35, 21, and 24 min, respectively, were identified as 125I-labeled EGF(1-52), EGF(1-48), and EGF(1-47). Proportions of different [125I]EGF derivatives formed depended on the segment of the gastrointestinal tract and the age of the animal. These C-terminally truncated [125I]EGF derivatives were fully immunoreactive and bound to EGF-specific receptors. However, receptor binding abilities were altered by C-terminal truncation. [125I]EGF(1-52) showed a greater receptor binding ability, whereas [125I]EGF(1-48) and [125I]EGF(1-47) showed lower bindings. These studies show that a significant portion of EGF delivered in gastrointestinal secretions may remain stable in the gastrointestinal lumen, and that EGF undergoes C-terminal truncation, producing three major EGF derivatives in the gastrointestinal lumen. The present studies also suggest that developmental differences may exist in the overall stability of EGF and amounts of different truncated EGF derivatives produced in the gastrointestinal lumen. © 1995.