Platelet alpha-adrenergic receptors in obesity: Alteration with weight loss

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Abstract
Platelet .alpha.-adrenergic receptor concentration and function was studied in 19 subjects with simple obesity participating in a double-blind, controlled clinical trial of diet and anorexiants (phentermine, fenfluramine or a combination of the 2) or placebo. From wk 1 to wk 8, weight loss for the group as a whole was 4.9 .+-. 0.7 kg (mean .+-. SE [standard error]). Concomitant with this weight loss, the platelet .alpha.-adrenergic receptor concentration rose from 85.7 .+-. 5.8 to 113 .+-. 5.8 fmol/mg protein. This increase moved the values for the obese subjects toward or beyond values in lean controls (100 .+-. 10.5 fmol/mg protein). The response in the different treatment groups was similar. The receptor concentration increase was accompanied by a corresponding increase in .alpha.-adrenergic receptor-mediated platelet aggregation. For individual subjects the extent of weight loss over time generally correlated with percent receptor change. Altered adrenergic sensitivity occurring in obese subjects who are losing weight may have important implications in relation to external (therapeutic or inadvertent) administration of catecholamines.