Amniotic fluid: Source of trophic factors for the developing intestine

Table 4 Roles of various trophic factors found in amniotic fluid in intestinal development and the location of their receptors

Trophic factor	Location of receptors	Role in intestinal growth
EGF	Basolateral intestinal membrane	Stimulates cell mitosis and differentiation
		Stimulates intestinal epithelial cell proliferation
HGF	Intestinal crypt epithelial cells and in the muscle layers of the intestine	Intestinal cell proliferation in vitro and has been demonstrated to induce intestinal growth in rats
TGF-α and TGF-β	Basolateral intestinal membrane	Primary role may be intestinal mucosal repair
IGF-1	Crypt cells, basolateral membrane and in the distal intestine	Primary mediator of both intrauterine and postnatal growth in mammals
		May be important for growth of muscle growth of distal small intestine
EPO	Apical surface of intestinal epithelial cells	Increased villus height, villus area, crypt depth and crypt epithelia cell proliferation in rat pups. In vitro, recombinant EPO has been shown to protect cells against mucosal injury
G-CSF	Apical regions of the intestine	Role in epithelial cell maintenance
IL family	Intestinal epithelial cells	Enhances intestinal epithelial cell restitution. Enhances the integrity of the intestinal epithelial cell junctions. Intestinal epithelial cell proliferation and increased nutrient uptake

IGF-1: Insulin like growth factor-1; EGF: Epidermal growth factor; TGF: Transforming growth factor; HGF: Hepatocyte growth factor; EPO: Erythropoietin; G-CSF: Granulocyte colony stimulating factor; IL: Interleukin.