Division of Nutrition Pathology, Institute of Animal Breeding, University of Berne, Switzerland.
The absorption of recombinant human insulin-like growth factor I(rhIGF-I), [125I]rhIGF-I, xylose and [3H]lysine, administered into a clamped jejunal segment in anesthetized neonatal calves, was studied by measuring their appearance in the mesenteric vein draining the gut segment. Only trace amounts of IGF-I and of [125I]rhIGF-I and/or 125I were absorbed following dissolution in saline, buffer or colostrum. The absorption rate of both [3H]lysine and/or 3H and of xylose was much greater than the absorption of rhIGF-I, [125I]rhIGF-I and/or 125I but was also transient. Biological effects of ingested IGF-I in neonatal calves should barely occur as a consequence of intestinal absorption even in 1-day-old calves, known to absorb various peptides and proteins.