1. Plasma noradrenaline and adrenaline concentrations were measured in ten subjects before, during and after intravenous infusion of angiotensin II (ANG II) in order to determine the sympathoadrenal response of ANG II challenge in man. In five subjects ganglionic blockade was additionally performed by intravenous infusion of trimethaphan.
2. During ANG II infusion mean arterial blood pressure increased by 30% (P<0.001), and plasma noradrenaline decreased by 25% (P<0.001). Plasma adrenaline decreased less.
3. During ganglionic blockade plasma noradrenaline decreased significantly (P<0.005) and similarly to the decrease obtained with ANG II infusion.
4. The results indicate that a decrease in sympathoadrenal activity occurs during ANG II-induced acute hypertension in man. This may be elicited by the arterial baroreflex, which seems to dominate any direct sympathoadrenergic facilitating effect of ANG II.