β-Adrenoceptor-Adenosine 3′,5′-Monophosphate System in Human Leucocytes before and after Treatment for Hyperthyroidism*

Modifications in characteristics of the beta-adrenoceptor-cAMP system were observed in leucocytes from 10 patients in the hyperthyroid state after antithyroid treatment. These include 1) an increased number of beta-adrenoceptors without a change in their affinity, 2) an increased magnitude of stimulation of adenylate cyclase by isoprenaline, without a change in the NaF-stimulated enzyme activity, 3) an increased cAMP-dependent protein kinase activity ratio, and 4) an increased activity of cAMP-phosphodiesterase. Moreover, the plasma cAMP levels were markedly elevated during the hyperthyroid state. It is suggested that the above changes may in part constitute the molecular basis for the reputed catecholamine supersensitivity in the hyperthyroid state.