Concentration of insulin-like growth factors (IGF-I and IGF-II) in tissues of developing lean and obese pig fetuses

An ontogeny study of lean and pre-obese pig fetuses was conducted to evaluate the temporal and genetic influence on the relationship between growth and IGF production. At 70, 90 and 110 days of gestation, three fetal pigs were obtained from each of three obese and lean dams. The heart, kidneys, lungs, liver and one biceps femoris muscle were removed, weighed, frozen and extracts prepared. For all the organ and tissue weights, there were significant (P less than .001) main effects of genotype (G) and fetal age (A). At each fetal age, pre-obese fetuses had lighter organ and tissue weights. The content of IGF's in serum and various tissues and/or organs was also determined. Main effects of A and G were significant (P less than .05) for liver and lung IGF-I and muscle IGF-II concentrations. Main effects of G were significant (P less than .01) for liver IGF-II whereas muscle IGF-I and lung IGF-II concentrations were only affected by fetal age (P less than .01). Overall, liver IGF-I and II and muscle IGF-II concentrations were higher in lean fetuses (P less than .01). Serum IGF-I concentration increased (P less than .01) with fetal age and was independent of fetal strain. Serum IGF-II concentration increased with age (P less than .01) in lean but not pre-obese fetuses. Therefore, these studies demonstrate genotype dependent growth factor concentrations in tissues and organs of developing fetuses. Finally, serum concentration of IGF's were strongly correlated (positive) with overall growth but were not strongly correlated with tissue and organ concentration of IGFs.