Elevated sympathetic nerve activity in borderline hypertensive humans. Evidence from direct intraneural recordings.

TLDR

Reports of elevated plasma catecholamines and augmented responses to autonomic blockade suggest increased sympathetic tone in borderline hypertension, yet it remains unclear whether this reflects greater sympathetic neural outflow. The study aimed to determine whether borderline hypertensive men exhibit elevated sympathetic nerve activity. Muscle sympathetic nerve activity was recorded by microneurography in 15 normotensive and 12 borderline hypertensive men while supine heart rate, blood pressure, plasma norepinephrine, and efferent muscle sympathetic nerve activity were measured after six days of low (10 meq Na⁺/24 hr) and high (400 meq Na⁺/24 hr) dietary sodium intake. Borderline hypertensive individuals had significantly higher sympathetic nerve activity on both low and high sodium diets and higher systolic and diastolic blood pressures independent of sodium intake; high sodium intake reduced sympathetic activity, norepinephrine, diastolic BP, heart rate, and increased weight in both groups, with a group‑by‑diet interaction observed for norepinephrine levels. Abstract truncated at 250 words.

Abstract

Reports of elevated plasma catecholamine levels and augmented responses to autonomic blockade suggest increased sympathetic tone in borderline hypertension. It is not known if this reflects greater sympathetic neural outflow. We directly recorded muscle sympathetic nerve activity (microneurography) in 15 normotensive and 12 borderline hypertensive age-matched men to determine whether borderline hypertensive individuals have elevated sympathetic nerve activity. Supine heart rate, blood pressure, plasma norepinephrine, and efferent muscle sympathetic nerve activity (peroneal nerve) were measured after 6 days of both low and high dietary sodium intake (10 and 400 meq sodium/24 hr). Sympathetic nerve activity was elevated significantly in borderline hypertensive individuals on both low (37 +/- 1 in borderline hypertensive individuals vs. 29 +/- 1 bursts/min in normotensive individuals; p less than 0.01) and high (25 + 1 in borderline hypertensive individuals vs. 16 +/- 1 bursts/min in normotensive individuals; p less than 0.01) sodium diets. The borderline hypertensive group had higher systolic (p less than 0.01) and diastolic (p less than 0.05) blood pressures independent of sodium intake. Across both groups, high sodium intake reduced muscle sympathetic nerve activity (p less than 0.001), plasma norepinephrine (p less than 0.001), diastolic blood pressure (p less than 0.02), heart rate (p less than 0.002), and increased weight (p less than 0.005). A significant (p less than 0.05) group-by-diet interaction was observed for plasma norepinephrine levels. Specifically, compared with the normotensive group, plasma norepinephrine levels in the borderline hypertensive group tended to be higher on low sodium diet (p = 0.08) and lower on high sodium diet (p = 0.23). (ABSTRACT TRUNCATED AT 250 WORDS)