Effects of physiological and pharmacological variation of sympathetic nervous system activity on plasma non-esterified fatty acid concentrations in man.

Abstract

1. The consequence of the sympatholytic effect of clonidine (alpha 2‐ adrenoceptor agonist) was compared with the effect of a physiological inhibition of sympathetic nervous system activity (change from upright to supine position) on plasma catecholamine and non‐esterified fatty acid (NEFA) concentrations in overnight fasting healthy men. 2. Clonidine (150 micrograms orally) administered in upright position induced a significant reduction of plasma noradrenaline and NEFA concentrations. A change from upright to supine position which provoked a more marked decrease in plasma noradrenaline concentrations induced a weak increase in plasma NEFA concentrations. 3. The modification of plasma NEFA and catecholamine concentrations brought about by standing up was studied after placebo or yohimbine (alpha 2‐adrenoceptor antagonist) administration. With placebo, standing up promotes a 100% increase in plasma noradrenaline concentrations (measured 5 and 15 min after rising) and a weak transient decrease in plasma NEFA concentrations (5 min after rising). In the supine position, yohimbine increased plasma noradrenaline and NEFA concentrations by about 100% and 55% respectively. Standing after yohimbine administration promoted large increases in plasma noradrenaline and NEFA concentrations. 4. These results indicate that a reduction of sympathetic nervous activity is not associated with a decrease of plasma NEFA concentrations and argue for a role of alpha 2‐adrenoceptors in the NEFA mobilization from adipose tissue after sympathetic nervous system activation in man.