Studies on the metabolic effects induced in the rat by a high-fat diet. Control of glucose metabolism in adipose tissue of fed and fasted rats.

Abstract

Epididymal adipose tissue of rats fed a high-fat diet and submitted or not to a 24-h fast before the experiment, was incubated with 10 mM glucose labelled with 14C at C-6, C-1 or universally, in the presence of insulin (1000 μU/ml). The results were used to estimate the glucose carbon flow through the various metabolic pathways and to establish a balance of production and utilization of reducing equivalents in the cytoplasmic compartment. Although previously altered by the fat diet, glucose metabolism is shown to be still highly sensitive to the effect of fasting which mostly results in a further reduction of fatty acid synthesis and in a further increase of glucose conversion into lactate. This effect is rather parallel to the known effect of fasting on glucose metabolism in adipose tissue of rats fed a normal fat-poor diet. In adipose tissue of rats fed a fat diet, the lactate/pyruvate ratio reaches an abnormally high value which is consistent with a calculate excess of production over utilization of reducing equivalents. A 24-h fast induces a drop of the lactate/pyruvate ratio together with a significant improvement of the balance between production and utilization. Thus, this effect is quite in opposition with the slight increase in the NADH : NAD+ ratio currently observed in adipose tissue of fasted rats after a normal fat-poor diet. It can be concluded from the results of this work that the cytoplasmic redox potential is not a major factor in the control of glucose metabolism in adipose tissue.