The effects of phenformin and metformin on fat and carbohydrate metabolism

In order to investigate the effects of two biguanide drugs, phenformin and metformin, on metabolic and hormonal changes with exercise, 6 healthy volunteers have been studied during and after 30 min of controlled moderate exercise on a bicycle ergometer on three occasions, two being for the drugs taken separately and the other without any drug, as a control study. Blood samples were taken for estimation of glucose, pyruvate, lactate, free fatty acids (FFA), glycerol, growth hormone (HGH) and insulin (IRI). Both drugs caused a greater rise in blood pyruvate and lactate concentrations during exercise compared with the changes in the control investigation. They also caused a delay in the disposal of pyruvate after exercise. In all investigations, the concentrations of FFA and glycerol rose to similar values at the end of exercise. In the control study, however, the pre-exercise value was achieved by the end of the investigation, whereas with the drugs the concentrations remained elevated. After exercise the rise of ketone-body concentrations was greater with the drugs. These observations indicate that the drugs interfere with aerobic utilization of metabolic fuels, reducing the utilization of pyruvate and glycerol and decreasing the rate of fat re-esterification: these metabolic effects are potentiated by exercise.