ENHANCED GROWTH OF SMALL-BOWEL IN TRANSGENIC MICE OVEREXPRESSING BOVINE GROWTH-HORMONE

Background: Transgenic mice with a bovine growth hormone gene linked to a mouse metallothionein I promoter (growth hormone transgenics) are a model of chronic growth hormone excess. Methods: Growth of small bowel mucosa in ad libitum-fed growth hormone transgenics and wild type littermates and in growth hormone transgenics pair fed with wild-type littermates were compared. Results: In both groups, body weight and small bowel weight were greater in growth hormone transgenics. Similarly, mucosal mass was 50%-100% greater in growth hormone transgenics, and the effect was greatest in proximal bowel. Villus height, measured in jejunum, was also greater in growth hormone transgenics. Measurements of mucosal proliferation did not differ between the growth hormone transgenics and wild type. Abundance of insulinlike growth factor-I messenger RNA in bowel was greater in growth hormone transgenics. Conclusions: Chronic growth hormone excess results in increased growth of small bowel mucosa. This effect appears to be specific because it occurred in ad libitum-fed and diet-restricted growth hormone transgenics, influenced villus height, and was more pronounced in upper than lower small bowel. The effect of chronic growth hormone excess does not appear to be secondary to an increase in the rate of mucosal proliferation, suggesting an effect on lifespan of mucosal cells. © 1993.