Effects of chronic low doses of d-fenfluramine on weight gain and calorie intake, brown adipose tissue thermogenic parameters and brain neurotransmitter content in rats fed chow or palatable diets.

Male black-hooded rats of original age 3 months were maintained on either a standard laboratory chow diet or a palatable diet (32 animals in each group). After two months, when clear increases in weight gain and calorie intake in the latter group were evident, eight animals from each group were killed for analysis. For one further month, eight animals from each group received low doses (1-3 mg/kg/day) of d-fenfluramine in drinking water, another eight served as untreated controls, and the remaining eight were pair-fed to the treated groups. On killing, the interscapular brown adipose tissue (BAT) mass, and also BAT mitochondrial protein and uncoupling protein contents, and BAT mitochondrial cytochrome oxidase activity and GDP-binding were measured. Gross brain chemical changes were assessed by measuring whole brain contents of serotonin, noradrenaline and dopamine. The palatable diet produced clear increases in weight gain, calorie intake, total BAT mass, BAT mass with respect to body mass, total BAT mitochondrial protein and total amounts of uncoupling protein in each case; however, BAT mitochondrial protein per unit of BAT mass was not significantly increased, nor was the amount of uncoupling protein per mg of mitochondrial protein. Small, but variable, increases in brain neurotransmitter contents were observed. Drug-treated animals showed marked reductions in calorie intake and body weight compared to untreated controls but no significant decreases in body weight compared to pair-fed controls were evident. The pair-fed (i.e. 'slimming') groups displayed a decrease in BAT thermogenic parameters: d-fenfluramine partially prevented these decreases.