Platelet Radioligand Binding and Neuroendocrine Challenge Tests in Depression

Abstract

The purpose of this work was to examine the number and function of α₂-adrenoceptors and the number of serotonin uptake sites in depressed patients and controls. Platelet α₂-adrenoceptors and platelet serotonin uptake sites were labelled with [³H]yohimbine and [³H]imipramine respectively. Central α₂-adrenoceptor function was assessed by growth hormone and other responses to challenge with the α₂-agonist clonidine. No overall difference in the binding parameters was observed between the control and depressed groups, but the results highlight the importance of drug-free interval, menopausal status and membrane protein concentration within the binding assays in the interpretation of such studies. The growth hormone response to clonidine tended to be blunted in depressed females and was significantly blunted in the subgroup of depressives who failed to suppress plasma cortisol concentrations in response to dexamethasone. Depressed subjects also showed a smaller decrease in diastolic blood pressure and a smaller increase in sedation than control subjects.