EFFECTS OF PHYSIOLOGICAL AND PHARMACOLOGICAL VARIATION OF SYMPATHETIC NERVOUS-SYSTEM ACTIVITY ON PLASMA NONESTERIFIED FATTY-ACID CONCENTRATIONS IN MAN

1 The consequence of the sympatholytic effect of clonidine (alpha2-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 mug 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 (alpha2-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 alpha2-adrenoceptors in the NEFA mobilization from adipose tissue after sympathetic nervous system activation in man.