We have used concentrations of plasma catecholamines to indicate activity of the sympathetic nervous system (SNS) in patients with essential hypertension, orthostatic hypotension, the hyperdynamic circulatory state syndrome, or sympathectomies. We developed clinical methods to estimate synaptic cleft concentrations of norepinephrine (NE), the sympathetic neurotransmitter; neuronal NE uptake (Uptake-1); and regional NE removal. We used clonidine suppression testing to identify patients in whom increased SNS activity contributed to high blood pressure. Measurement of arterial and venous NE in sympathectomized and intact human limbs confirmed the validity of plasma NE to indicate SNS activity. Patients with idiopathic orthostatic hypotension had decreased Uptake-1 activity. Elevated plasma catecholamines, clonidine sensitivity, and excessive responsiveness to isoproterenol characterized a patient with hyperdynamic circulaion syndrome. The amount of release of endogenous NE during isoproterenol infusions may indicate pre-synaptic beta adrenoceptor responsiveness. Dopamine does not act as a natriuretic hormone.
