Growth Allometry of the Organs in Giant Transgenic Mice*

We have analyzed the absolute and relative (allometric) growth of a series of internal organs in giant transgenic (MTrGH) and littermate control mice to determine the general and organ-specific effects of the altered hormonal environment on growth in these rodents. Comparison of cross-sectional growth allometries of organ weights and external body dimensions between the two samples was based on analyses of covariance. We report significantly increased growth in all of the organs and measurements examined except for the brain. Coefficients of growth allometry differ significantly from isometric values in a number of cases, and thus, the adult transgenic mice exhibit body proportions different from those of the adult controls. Most of these shape differences reflect general allometric size increase, but the liver and spleen of the transgenics undergo special enlargement or growth. These results indicate that the primary effect of elevated GH and IGF-I levels is increased overall growth, but in the relative proportions set by the intrinsic controls of individual organs and body regions.