Changes induced by corticosterone and adrenalectomy in synaptosomal and platelet uptake and binding of 5-HT. The relationship to [3H]imipramine binding.

A comparative study of the effect of adrenalectomy, treatment with corticosterone, and imipramine on platelet an synaptosomal uptake was undertaken. One day after adrenalectomy, uptake of 5-hydroxytryptamine (5-HT) in the platelet and the hypothalamus was significantly decreased with an increase in the apparent Km, but the uptake of 5-HT of the cerebral synaptosomes was unchanged. In this group, the Kd of low affinity binding of 5-HT was also increased in the hypothalamic synaptosomes and in the platelet preparations. Treatment with corticosterone (5 mg/kg, i.m.) restored the decrease in the uptake of 5-HT induced by adrenalectomy in the hypothalamic synaptosomes and in the platelets, and significantly increased the uptake of 5-HT of these fractions in sham-operated rats. The binding of 5-HT was unchanged by acute treatment with corticosterone. The effectiveness of imipramine varied with the preparation and treatment group. The IC50 of the cerebral synaptosomal preparation was greater than that of the hypothalamic synaptosomal preparation. Using this latter preparation, the IC50 for imipramine in adrenalectomised, sham-operated and corticosterone-treated rats were found to be 0.04, 0.09 and 0.25 microM, respectively. These changes in sensitivity to imipramine were not reflected in the binding of [3H]imipramine which was unchanged.