Acute effect of ephedrine on 24-h energy balance

Ephedrine is used to help achieve weight control. Data on its true efficacy and mechanisms in altering energy balance in human subjects are limited. W e aimed to determine the acute effect of ephedrine on 24-h energy expenditu re, mechanical work and urinary catecholamines in a double-blind, randomize d, placebo-controlled, two-period crossover study. Ten healthy volunteers w ere given ephedrine (50 mg) or placebo thrice daily during each of two 24-h periods (ephedrine and placebo) in a whole-room indirect calorimeter, whic h accurately measures minute-by-minute energy expenditure and mechanical wo rk. Measurements were taken of 24-h energy expenditure, mechanical work, ur inary catecholamines and binding of(+/-)ephedrine in vitro to hu man beta(1 )-, beta(2)- and beta(3)-adrenoreceptors. Twenty-four-hour energy expend it u re was 3.6% greater (8965+/-1301 versus 8648+/-1347 kJ, P < 0.05) with ep hedrine than with placebo, but mechanical work was not different between th e ephedrine and placebo periods. Noradrenaline excretion was lower with eph edrine (0.032+/-0.011 mu g/mg creatinine) compared with placebo (0.044+/-0. 012 mu g/mg creatinine) (P < 0.05). (+/-)Ephedrine is a relatively weak par tial agonist of hu man beta(1)- and beta(2)-adrenoreceptors, and had no det ectable activity at human beta(3)-adrenoreceptors. Ephedrine (50 mg thrice daily) modestly increases energy expenditure in normal human subjects. A la ck of binding of ephedrine to beta(3)-adrenoreceptors and the observed decr ease in urinary noradrenaline during ephedrine treatment suggest that the t hermogenic effect of ephedrine results from direct beta(1)-/beta(2)-adrenor eceptor agonism. An indirect beta(3)-adrenergic effect through the release of noradrenaline seems unlikely as urinary noradrenaline decreased signific antly with ephedrine.