Regulation of bone characteristics by altered body composition in bGH transgenic mice.
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Effects of mutant bGH genes (G119K, Mil, M4) expressed in mice on bone, lipid and protein deposition, and their relationships were compared to control mice (NTC). The G119K mutant deposited less protein and equal quantities of adipose as NTC. The Mil line was similar to NTC, whereas M4 mice were larger (P < 0.01), and deposited more protein and fat than NTC. The most interesting relationships were for tibia weight, ratio of tibia weight:empty body weight, deformation to flexure, and modulus of elasticity (MOE). In NTC, Mil and M4 mice, tibia weight increased with protein gain (P < 0.001). For G119K, tibia weight increased slightly with protein gain, but the increase with fat gain was similar to NTC mice (P < 0.001). The ratio of tibia weight:empty body weight increased equally in response to protein and fat gain in NTC mice. In all transgenics, this ratio increased with protein gain and decreased with fat gain (P < 0.002). Deformation to flexure was negatively affected by protein gain in NTC and Mil mice. In comparison, the decline with protein gain in G119K and M4 mice was small, with the least deformation occurring with maximum fat weight (P < 0.02). MOE increased with protein gain, but declined with small increases in fat weight in NTC mice. Declines occurred with near maximum fat weights for the Mil, G119K, and M4 mice. In Mil and G119K mice, MOE increased with protein gain. However, MOE declined with protein gain in M4 mice (P < 0.001). The data suggested either a differential effect on specific tissue types by the bGH analogs, or an alteration in patterns of nutrient utilization, especially to meet the increased soft tissue demands in M4 mice. Key Words: Transgenic Mice, bGH, Composition, Skeleton.