IGF-I and IGF-II receptors are expressed in the small intestine of mammalian species,
as are the genes to synthesize both peptides. IGF binding proteins are also expressed
in the intestine. IGF-I and IGF-II mRNA are highest in fetal and newborn tissues and
decrease with age. IGF-I mRNA is present in the adult small intestine, and is associated
with the submucosal regions and crypt cells. IGF-I and IGF-II receptor binding to
the small intestine is higher in newborn animals and decreases with age. Both receptors
are more concentrated in the crypt than villus regions, but IGF-II binding is higher
than IGF-I in all regions. IGF-I receptors are associated with the submucosal region
of the small intestine, whereas IGF-II receptors are more abundant in the mucosal
cells. Administration of IGF-I either orally or by osmotic pump generally has no affect
on small intestinal weight or length, but does increase mucosal cellularity. LR3-IGF-I administration by osmotic pump affects the small intestine similarly to IGF-I,
although with a higher potency. In the few studies in which IGF-II was administered,
increased gut mass was observed in adult rats, but not newborn rats or pigs. Significant
effects on mucosal expression of disaccharidases was achieved with either oral or
subcutaneous IGF-I or oral IGF-II. Administration of IGF in models of intestinal hypertrophy
and atrophy are also reviewed.
Key words
Receptors - Disaccharidases - Mucosal Cells - Bowel Resection - Parenteral Feeding
- Transgenic - Development
