Estimation of 'total' renal, cardiac and splanchnic sympathetic nervous tone in essential hypertension from measurements of noradrenaline release.

The overall rate of release of noradrenaline to plasma was increased in 31 patients with essential hypertension; the median value was 32% (526 pmol/min) higher than in 22 subjects with normal blood pressure. To ascertain the pattern of sympathetic nervous system activation underlying this abnormality, regional sympathetic nervous activity was estimated, from radiotracer-derived estimates of organ-specific noradrenaline release to plasma, in the kidneys, heart and hepatomesenteric circulation. Renal sympathetic nervous tone was preferentially increased in essential hypertension, especially in young patients with hypersecretion of renin. Cardiac noradrenaline release (and possibly cardiac sympathetic tone) was also higher in hypertensive patients; the difficulty in interpretation here arises because left ventricular mass is also increased in essential hypertension. Approximately half of the surfeit in total noradrenaline release to plasma noted in hypertensive patients was accounted for by the increased cardio-renal noradrenaline release. The balance comes from undetermined sites, but not from the splanchnic circulation, in which sympathetic nervous activity was not increased.