EXPRESSION OF MUTANT BOVINE GROWTH-HORMONE GENES IN MICE PERTURBS AGE-RELATED NUTRIENT UTILIZATION PATTERNS

Three lines of transgenic mice expressing mutant bovine growth hormone (bGH) genes and displaying small (G119K), near normal (M11) or large (M4) phenotypes and nontransgenic control (NTC) mice were used to dete rmine GH-associated, age-specific changes in empty body composition. T he single amino acid substitution in G119K mice reduced the quantities (P < 0.001) and early rates (P < 0.05) of deposition for water, prote in and ash but resulted in similar quantities of fat as the NTC mice. The change in relative quantities of empty body components indicated t he G119K analogue altered nutrient partitioning, basal metabolism and (or) nutrient availability to effect the differential observed in body composition. The two amino acid substitutions in the bGH gene express ed by the M11 mice caused only a small change in phenotype, but age-re lated changes in the accretion of protein, fat and ash indicated these mice were not mature by 68 d of age. The bGH analogue produced by the M4 mice resulted in a doubling (P < 0.001) of body weight in comparis on with the NTC mice, a result of the increasing (P < 0.001) rate of w eight gain. Empty body component gain of the M4 mice also indicated th ey had not yet matured by 68 d of age. The G119K and M4 mutant forms o f bGH altered rates and composition of growth, possibly through redire ction of tissue nutrient utilization, modification of nutrient metabol ism, and(or) nutrient availability.