Increased sympathetic outflow in cirrhosis and ascites: direct evidence from intraneural recordings.

OBJECTIVE: To determine if central sympathetic outflow is increased in patients with cirrhosis and ascites. PATIENTS: Eleven patients with cirrhosis and ascites, 8 patients with cirrhosis but without ascites, and 7 age-matched and 8 young healthy volunteers.
METHODS: With subjects supine, direct microneurographic recordings of efferent post-ganglionic muscle sympathetic nerve activity were obtained from the peroneal nerve, and sympathetic burst frequency was compared with subjects' blood pressure, heart rate, sodium excretion, catecholamines, and plasma renin activity. All patients with cirrhosis were studied at least 5 days after withdrawal from all medications and after 7 days of a 20 mmol/d sodium, 1-L fluid-restricted diet. Age-matched volunteers were studied after 7 days of 20 mmol/d sodium intake and young healthy volunteers after 7 days of 150 mmol/d sodium intake.
RESULTS: Sympathetic nerve activity in ascitic patients (65 +/- 15 bursts/min; mean +/- SD) was markedly increased, whether compared with patients with cirrhosis but without ascites (34 +/- 16 bursts/min; P less than 0.001), age-matched healthy volunteers on similar sodium intake (27 +/- 22 bursts/min; P less than 0.001), or young healthy subjects (21 +/- 10 bursts/min; P less than 0.001). The frequency of muscle sympathetic nerve discharge was directly related to plasma norepinephrine and epinephrine concentrations, plasma renin activity, and heart rate, all of which were increased in those patients with cirrhosis and ascites, and inversely related to 24-hour urinary sodium excretion, the fractional excretion of sodium, and subjects' pulse pressures. Sympathetic nerve activity fell from 78 to 6 bursts/min in one patient after liver transplantation.
CONCLUSIONS: This study provides the first direct evidence that elevated plasma norepinephrine concentrations in patients with cirrhosis and ascites are due to increased central sympathetic outflow. Sympathetic nerve activity is not increased in patients with cirrhosis but without ascites. Because there were direct positive correlations of sympathetic nerve activity with plasma norepinephrine concentrations, plasma epinephrine concentrations, plasma renin activity, and heart rate, the increase in central sympathetic outflow in patients with cirrhosis and ascites appears generalized and not restricted to muscle nerves. The anti-natriuretic effects of parallel increases in renal and muscle sympathetic nerve activity could account for the inverse correlation between muscle sympathetic nerve activity and sodium excretion.