1. Dopamine in 5% (w/v) d-glucose was infused into five healthy male volunteers at doses of 2, 5 and 10 μg min−1 kg−1 over three sequential periods of 45 min each.

2. Oxygen consumption, respiratory exchange ratio, blood glucose concentration and plasma levels of free fatty acids, glycerol, lactate, dopamine, adrenaline and noradrenaline were measured. The results were compared with values obtained during infusion over the same time period of the corresponding volumes of 5% (w/v) d-glucose alone.

3. Energy expenditure calculated from the oxygen consumption and the respiratory exchange ratio was higher than control values during infusion of dopamine (P < 0.001, analysis of variance) specifically at a rate of 10 μg min−1 kg−1 (P < 0.05) when it was 14% higher, but not at a rate 2 of or 5 μg min−1 kg−1. The plasma noradrenaline concentration was 74 and 230% and the blood glucose concentration was 21 and 36% higher than control values at 5 and 10 μg of dopamine min−1 kg−1, respectively (P < 0.01). At 10 μg of dopamine min−1 kg−1 the plasma free fatty acid concentration was 70% and the plasma glycerol concentration was 80% higher than during the control infusion (P < 0.01). The respiratory exchange ratio and the plasma lactate concentration were the same in the two groups and did not alter during the dopamine infusion. The plasma adrenaline concentration rose significantly (P < 0.01), but only transiently, during dopamine infusion at a rate of 2 μg min−1 kg−1.

4. Dopamine at low doses has metabolic effects. It increases the blood glucose concentration and the circulating noradrenaline level at an infusion rate of 5 μg min−1 kg−1. It increases energy expenditure and circulating free fatty acid and glycerol levels at an infusion rate of 10 μg min−1 kg−1, presumably due to stimulation of lipolysis.

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