Spontaneous and 2DG induced metabolic changes and feeding: the ischymetric hypothesis

A computer-controlled calorimeter which simultaneously measured respiratory exchanges, locomotor activity, and meal patterns, was used to study Total Metabolic Rate (TM), Locomotor Free Metabolic Rate (LFM), and Respiratory Quotient (RQ) in relation to spontaneous and 2DG induced Food Intake in freely-feeding rats. It appeared that spontaneous and 2DG induced feeding was preceded by a consistant drop of LFM starting about five minutes before a meal and reaching its nadir at the onset of a meal. The simultaneous determination of the RQ did not show any systematic change that would have reflected either a lipo- or a gluco-privic origin of the LFM drop and meal onset. Therefore, the results are in agreement with the ischymetric hypothesis of the control of food intake which proposes that the final signal triggering hunger and satiety is the intensity of cell power production (measured in this experiment through the LFM parameter) which is independent of the glucidic lipidic or protidic origin of the substrate(s) supplying power production.