Metabolic rate and feeding behavior.

According to the ischymetric hypothesis, hunger is induced by the decrease of overall metabolic rate. In order to assess such a mechanism, it was necessary to monitor the muscular contraction-free metabolic rate designated "métabolisme de fond" (MF) in rats that were either resting or moving. MF was then examined in relation to either spontaneous or induced feeding patterns. A computerized open-circuit gas analysis system allowed us to monitor MF and behavior and to show that the onset of a spontaneous meal was preceded by a decrease of MF and its termination is preceded by a rebound of MF. Pharmacological blockade of utilization of both glucose and lipids enhanced feeding only to the extent that it reduced MF. These findings apply to pharmacotherapy because the anorexigenic effect of dexfenfluramine results from the enhancement of MF induced by the capacity of this drug to mobilize endogenous fat reserves and to so provide an endogenous meal that inhibits the exogenous meal. The ischymetric mechanism of hunger does not exclude important modulatory input from hormonal, circadian, and environmental factors in the control of feeding.