Dextrofenfluramine increases energy cost of muscular effort.

A peripheral action of dextrofenfluramine (d.FF) was investigated. The effects of d.FF on total energy expenditure (TEE), locomotor activity (LA), and respiratory quotient (RQ) were quantitatively monitored for 22 hours by a computerized metabolic device. The precise temporal evolution of RQ allowed calculation of glucidic versus lipidic substrates used in all instances. It appeared that in d.FF-treated rats, TEE and resting energy expenditure (REE) were not significantly changed, RQ and LA were significantly decreased. Moreover, in d.FF-treated rats. LA induced a two to five fold increase energy expenditure over vehicle-treated control subjects and it was observed that there was an LA related increase in RQ which was not observed in control subjects. Therefore, d.FF causes LA to be a highly inefficient process by inducing what seems to be an exaggerated catabolism of glucides. These may be only partially used for muscular contraction because it was calculated from relative changes in RQ and TEE during LA that 70% of the catabolized glucides seems to be diverted toward lipogenesis. This process probably represents the way futile cycles are triggered by d.FF in order to exacerbate LA associated energy cost.