Influence of age and genetic background on in vivo fatty acid synthesis in obese (ob/ob) mice.

The relationship of developing obesity and hyperinsulinaemia to fatty acid synthesis in whole body and major tissues has been studied in two strains of genetically obese (ob/ob) mice using in vivo incorporation of 3H2O into fatty acids. Rates of fatty acid synthesis were not increased in pre-weaning C57BL/6J obese mice even though hyperinsulinaemia and obesity occurred. Post-weaning, rates of fatty acid synthesis increased to 5 weeks of age in adipose tissue, liver and carcass, the latter being the major site of synthesis. Synthesis then declined in carcass and adipose tissue, but remained unchanged in liver at 3 months. Increased fatty acid synthesis developed earlier in Imperial College obese mice as compared to the C57BL/6J strain and total rates of synthesis were 3--5 times greater. Adipose tissue was the major site of synthesis in Imperial College obese mice, while carcass was of only minor importance. Thus genetic background and age strongly affected rates of fatty acid synthesis and also the extent to which various tissues contributed.