Sympathoadrenal activity and obesity: physiological rationale for the use of adrenergic thermogenic drugs

The sympathetic nervous system is a major regulator of dietary thermogenesis in laboratory animals and humans. Since a lowered metabolic rate predisposes to the development of obesity, and since caloric restriction suppresses sympathetic activity, a role for adrenergic agonists in the treatment of obesity has a well established physiological rationale. Although diminished sympathetic activity does not appear to underlie obesity in most circumstances in humans, to the extent that adrenergic agonists increase metabolic rate in the obese they may be useful as pharmacologic adjuncts to low energy diets. During caloric restriction the significant diminution in sympathetically mediated thermogenesis antagonizes weight loss; this decrease in metabolic rate may be overcome by sympathomimetic amines thereby increasing the effectiveness of low energy diets. Since smoking stimulates the sympathoadrenal system and increases thermogenesis, smoking cessation, with its attendant fall in sympathoadrenal activity and decrease in metabolic rate, fosters weight gain. Adrenergic agonists may be useful in this circumstance as well.