Growth hormone treatment increases transmural colonic growth in GH-deficient dwarf rats

Growth hormone (GH) has been implicated as an important factor in the growth regulation of several visceral organs including the gastrointestinal tract. Our aim was to study the effects of GH administration on colonic growth in dwarf rats with an isolated GH deficiency. Dwarf rats were treated with recombinant human growth hormone (rhGH; 2.0 mg/kg/day) for four weeks and compared with saline treated dwarf rats and rats with normal pituitary function. The colonic wall composition was measured by means of stereological techniques. RhGH treatment of the dwarf rats increased body weight by 80% and proximal and distal colon weight by 63% and 90%, when compared with placebo treated dwarf rats (P< 0.01). The weight of the proximal colonic mucosa increased by 83% (P< 0.01), submucosa by 78% (P< 0.05), and the muscularis propria by 51% (P< 0.001) in rhGH treated dwarf rats compared with dwarf controls. The weight of the distal colonic mucosa increased by 88% (P< 0.01), submucosa by 88% (P< 0.05) and the muscularis propria by 58% (P< 0.05) compared with dwarf controls. The growth of mucosa involved all mucosal layers, with a 73 and 92% increase in the proximal and distal colon luminal surface area respectively (P< 0.001, P< 0.01). The food consumption, expressed as g/day/100 g BW was 13% higher in dwarf rats receiving rhGH than in placebo treated rats (P< 0.05) and normal control rats (P< 0.05). When weights of the GI tract compartments are corrected for the increase in body weight the effects of GH treatment were small or non-significant. RhGH administration in GH deficient dwarf rats induces visceral growth with a pronounced increase in colonic luminal surface area and growth of all layers of the colonic wall. These findings confirm the important role of GH in the regulation of intestinal growth.