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A decrease of the basal glucose metabolism with senescence in the isolated rat adipose tissue has been demonstrated. In the presence of insulin, the oxidation of (U14C)-D-glucose and its incorporation into triglycerides are significantly increased at all ages studied. No significant difference between groups of animals was noted when the insulin-stimulating effect was related to basal metabolism. The synthesis of fatty acids from glucose is highly enhanced by insulin at 6 weeks, poorly at 6 months and no more at 24 months. It is concluded that the insulin sensitivity of the rat adipose tissue is not affected by ageing. Nevertheless, as far as fatty acid synthesis is concerned, a different metabolic pathway could be involved.

No modification in basal radioglucose metabolism by isolated rat diaphragm could be seen with senescence. Insulin increased the production of 14CO2 only in growing animals. On the opposite, incorporation of radioglucose into glycogen is enhanced in the different age groups; nevertheless, the response in 3-month-old animals was lower than in 6-week-old ones. No significant difference has been detected between the adult and the old rats. Therefore, it is concluded that a diminution of insulin sensitivity appeared during the period of transition between growing up and maturity without any further modification during old age.