Evidence in humans for a postsynaptic interaction between noradrenaline and angiotensin II with regard to systolic but not diastolic blood pressure

Much animal evidence exists to suggest that there is an interaction between noradrenaline (NA) and angiotensin II (AII). We have now sought evidence for a postsynaptic AII/NA interaction. Ten normotensive volunteers were infused with dextrose/saline, All/saline, dextrose/NA or AII/NA in a randomized single-blind fashion. The respective increases in systolic blood pressure (SBP) were -4 ± 6, -2 ± 9, 4 ± 6 and 14 ± 16 mmHg at comparative time intervals while the corresponding increases in diastolic blood pressure (DBP) were 2 ± 4, 6 ± 7, 9 ± 6 and 14 ± 8 mmHg. ANOVA confirmed that AII and NA had a synergistic interaction (P < 0.05) in elevating SBP while there was merely an additive effect in elevating DBP. Plasma NA and AII levels were unchanged by the coincidental presence of AII and NA, respectively, which excludes a generalized pharmacokinetic interaction between AII and NA. This study provides evidence for a postsynaptic AII/NA interaction with regard to SBP but not DBP although the precise location of this interaction remains uncertain. Therefore, in considering the pathogenesis of SBP abnormalities, concomitant measurements of both NA and AII may be important.