Total, and organ-specific, noradrenaline plasma kinetics in essential hypertension

We have developed radiotracer techniques, based on measurement of the rate of spillover of noradrenaline to plasma, to simultaneously estimate total, and organ-specific, sympathetic nervous activity in humans. In 27 unmedicated subjects without renal or liver disease, or cardiac failure, regional noradrenaline spillover rates were as follows: lungs 33% of total noradrenaline release to plasma, kidneys 22%, skeletal muscle 20%, hepatomesenteric 9%, skin 5%, and heart 3%. These findings have relevance to numerous previous studies on the importance of the sympathetic nervous system in the pathogenesis of human essential hypertension. The indices of overall sympathetic nervous tone which have been used, such as measurements of plasma noradrenaline concentration or total NA release to plasma, are seen to be not sufficiently specific, since the organs and regions thought to be central to hypertension pathogenesis (kidney, heart, splanchnic circulation) are responsible for no more than 35% of all noradrenaline released to plasma. Organ-specific noradrenaline spillover measurements are better suited to the elucidation of any sympathetic nervous system pathophysiology in human hypertension. Early results point to an increase in renal sympathetic tone in young patients with essential hypertension.