Mechanism of elevated plasma noradrenaline in the course of essential hypertension.

Increased sympathetic nervous system tone may be the initiating pathophysiologic event in some patients with essential hypertension. We estimated sympathetic nervous activity from radiotracer-derived measurements of noradrenaline release to plasma in 34 patients with essential hypertension and 23 subjects with normal blood pressure. The plasma concentration of noradrenaline (32% increased) and the rate of release of noradrenaline to plasma (38% increased) were elevated overall in patients with essential hypertension, largely due to higher noradrenaline release in hypertensive patients aged less than 40 years. Noradrenaline release from the kidneys and heart was elevated; renal noradrenaline spillover was 2.4 times normal in patients aged less than 40 years. Increased renal noradrenaline spillover accounted for 42% and increased cardiac noradrenaline spillover for 4% of the excess total noradrenaline spillover in essential hypertension, leaving 54% unexplained. Total noradrenaline spillover to plasma was normal in hypertensive patients aged 60 years and over. The plasma noradrenaline concentration was similar in younger and older hypertensive patients, despite lower noradrenaline release in the latter due to an age-dependent fall in noradrenaline plasma clearance in essential hypertension. Cardiorenal sympathetic nervous system tone appears to be increased in essential hypertension, particularly in younger patients. This contributes substantially to the higher plasma noradrenaline values found.