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

Abstract

The present study was designed to examine the specificity of β-adrenergic antagonists for β₁, β₂-adrenergic and 5HT_1B-serotonergic receptors by the competitive interaction with ¹²⁵I-iodocyanopindolol (¹²⁵I-ICYP) as a radioligand. The β₁-adrenoceptors were preferred by acebutolol, atenolol, betaxolol, practolol, and I-, dl and d-metoprolol, while butoxamine and ICI-118, 551 preferred β₂-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 5HT_1B-receptors. Good correlations were observed between the potencies of β-adrenoceptor antagonists for inhibition of ¹²⁵I-ICYP binding to β₁- and β₂-adrenoceptor sites and their potencies for inhibiting the binding of the same radioligand to 5HT_1B-serotonergic receptor sites. These results suggest that β-adrenoceptor antagonists can bind to β-adrenoceptors and 5HT_1B-receptors.