Alterations in beta-adrenergic sensitivity and platelet alpha 2-adrenoceptors in obese women: effect of exercise and caloric restriction.

1. Peripheral adrenergic responses were studied in eight obese women before and after 15 days of caloric restriction (2500 kJ/day) and in eight sex- and age-matched lean controls. 2. beta-Adrenergic sensitivity (defined as the dose of isoprenaline required to increase resting heart rate by 25 beats/min) was evaluated before and after the diet. Density and affinity (determined as the apparent dissociation constant) of platelet alpha 2-adrenergic receptors, and plasma adrenaline and noradrenaline levels, were measured after overnight bed-rest and after 9 min of standardized exercise performed before and after the low caloric diet. 3. Before the diet basal antecubital venous plasma noradrenaline concentrations were lower in obese women when compared with lean women (0.94 +/- 0.06 vs 1.27 +/- 0.17 nmol/l, P less than 0.02). Isoprenaline sensitivity did not differ between lean and obese women. 4. At rest, platelet alpha 2-adrenoceptor density was lower in overweight than in lean women (129 +/- 21 vs 168 +/- 16 fmol/mg of protein, P less than 0.02). Exercise significantly increased platelet alpha 2-adrenoceptor density and decreased affinity in lean women. This decrease correlated with the rise in plasma noradrenaline. 5. In obese women exercise did not modify platelet alpha 2-adrenoceptor density or affinity, despite a significant increase in plasma catecholamines. However, the increase in plasma noradrenaline during exercise was lower in obese women. 6. The low caloric diet produced a beta-adrenergic supersensitivity.(ABSTRACT TRUNCATED AT 250 WORDS)