The effects of different doses of dopamine and domperidone on increases of plasma norepinephrine induced by cold pressor test in normal man.

The effect of dopamine 1 and 3 micrograms/kg/min i.v., of dopamine 1 and 3 micrograms/kg/min i.v. combined with domperidone 30 mg per os and of placebo infusion on plasma norepinephrine concentration before and during sympathetic stimulation by a cold pressor test was investigated in 10 healthy volunteers (1 female, 9 males, mean age 28, range 19-41). Dopamine 1 microgram/kg/min resulted in a blunting of the rise in plasma norepinephrine concentration during the cold pressor test, compared with placebo infusion. The addition of domperidone to dopamine 1 microgram/kg/min abolished this effect. Plasma norepinephrine levels during dopamine 3 micrograms/kg/min infusion, both with and without domperidone, were not different from placebo, but significantly higher compared to dopamine 1 microgram/kg/min infusion. Dopamine 1 and 3 micrograms/kg/min infusion, both with and without domperidone resulted in a blunted increase in blood pressure compared to placebo infusion. Dopamine 1 microgram/kg/min infusion resulted in a lower systolic blood pressure during the cold pressor test compared to dopamine 3 micrograms/kg/min infusion. No significant changes in heart rate occurred during the cold pressor test comparing the different circumstances. We conclude that in healthy volunteers only dopamine 1 microgram/kg/min, but not dopamine 3 micrograms/kg/min, blunts the increase in plasma norepinephrine concentration during a cold pressor test; this effect is abolished by pretreatment with domperidone. We presume that for dopamine 1 microgram/kg/min the inhibitory effects of presynaptic DA-2 receptor or alpha-2 adrenoceptor stimulation on plasma norepinephrine concentration predominate. When dopamine 3 micrograms/kg/min is infused, the inhibitory effects might be counteracted by uptake-1 inhibition or enhanced synthesis and release of norepinephrine, either directly or indirectly.