Variation in Plasma Concentration of Insulin-like Growth Factor-l and its Covariation with Liveweight in Mice

Abstract

Three experiments were undertaken to examine the degree and causes of variation in plasma concentrations of insulin-like growth factor-l (IOF-I) in mice. The relationship between IOF-l concentrations and liveweight was also examined. In all three experiments, a number of non-genetic factors were found to contribute significantly to the variation in IOF-l concentrations, the most important of these being sex and litter size. In one experiment, where pups from 16 litters were cross-fostered to avoid the confounding of maternal and direct genetic effects, a heritability of 0'40 ± 0·27 was estimated for plasma IOF-l concentration at 35 days of age. To examine further the existence of genetic variation in plasma concentrations of IOF-l and the genetic covariation between plasma IOF-l levels and other body traits, a selection experiment with mice has been initiated. Moderate to strong phenotypic correlations between IOF-l concentrations and weight at an early age have been found in all three experiments.