Characteristics of 125I-lodocyanopindolol Binding to β-Adrenergic and Serotonin-1B Receptors of Rat Brain: Selectivity of β-Adrenergic Agents

The present study was designed to examine the specificity of β-adrenergic antagonists for β1-,β2-adrenergic and 5HT1B-serotonergic receptors by the competitive interaction with 125l-iodocyanopindolol (125I-ICYP) as a radioligand. The -adrenoceptors were preferred by acebutolol, atenolol, betaxolol, practolol, and I-, dl- and d-metoprolol, while butoxamine and ICI-118,551 preferred α2-adrenoceptors. The selectivities of these β1- and β2-antagonists are well-known, but alprenolol which is known as a non-selective antagonist was 7.2-fold more selective for the β2-adrenoceptors in the present study. All β-antagonists used were more selective towards β-adrenoceptors as compared with 5HT13-receptors. Good correlations were observed between the potencies of β-adrenoceptor antagonists for inhibition of 125I-ICYP binding to α1- and α2-adrenoceptor sites and their potencies for inhibiting the binding of the same radioligand to 5HT1B-serotonergic receptor sites. These results suggest that β-adrenoceptor antagonists can bind to β-adrenoceptors and 5HT1B-receptors.