Plasma catecholamines and autonomic responsiveness in obesity.

: The autonomic responsiveness of lean women to standing, passsive vertical tilting, noradrenaline infusion and the valsalva manoeuvre has been compared with that of obese women and a group of formerly obese women (post-obese). Upon standing, the lean and obese groups had comparable cardiovascular responses with similar rises in plasma noradrenaline. With passive 85 degrees head-up tilting at an ambient temperature of 26 degrees C the obese and post-obese subjects had a greater rise in plasma noradrenaline than the lean group who were less able to withstand the test. Noradrenaline infusions (at 26 degrees C) in the lean and post-obese subjects led to similar increases in plasma noradrenaline, systolic and diastolic pressures and plasma free fatty acids but the post-obese showed a greater bradycardia. The response to the valsalva manoeuvre was normal in lean and obese patients and was unaltered after a reduced energy intake in the obese. On energy restriction for two weeks 10 obese subjects showed a fall in pulse rate, in systolic and diastolic pressures and in plasma noradrenaline while the subjects remained supine. On standing there was less of a rise in plasma noradrenaline than when energy intake was high. The response in noradrenaline was restored to that seen on high energy intakes by giving L-dopa. Seasonal changes in venous noradrenaline concentrations were apparent in obese and post-obese patients but not in lean subjects. These differences may relate to altered responses to environmental temperature or to an altered food intake in the two obese groups. There appears to be no generalised in the autonomic system in obese women either before or after weight loss but the process of slimming does lead to a reduction in plasma noradrenaline levels.