Effect of maturation and senescence on carbohydrate utilization and insulin responsiveness of rat adipose tissue

The aim of the present investigation was to study the effect of aging upon the metabolism and the responsiveness to insulin of epididymal adipose tissue from rats (6 weeks, 6 and 24 months). Basal glucose metabolism by these tissues and adipocytes was positively related to cell size, for each age group. But age per se plays an important role: for the same diameter, the U-14C-glucose oxidation to CO2 and its incorporation into triglycerides described markedly between 6 weeks and 6 months, as reported peviously, and decreased still further between 6 months and 24 months, for any diameter. In contrast, insulin responsiveness of adipose tissue fragments and fat cells was negatively correlated to adipose cell size, when we analyzed the role of cell diameter for a group of given age. When comparing the sensitivity to hormone for a given cell volume but at different ages, it appeared that insulin resistance increased considerably between 6 weeks and 6 months and was still more marked in old age. The mechanisms underlying these facts have been discussed.