Comparative characterization of β-adrenoceptors in the bladder, heart, and lungs of rats: Alterations in spontaneously hypertensive rats

The present study aimed to characterize and compare β-adrenoceptors in the rat bladder with those in the heart and lungs of SD rats (8–10 weeks old) using subtype-selective agonists and antagonists in a radioligand binding assay with (-)-[125I]cyanopindolol ([125I]CYP), and also to clarify alterations in β-adrenoceptors in the bladder of spontaneously hypertensive rats (SHR) at 14 weeks old, from those of Wistar-Kyoto rats (WKY) and Wistar rats at the same age. A radioligand binding assay with [125I]CYP was used to measure β-adrenoceptor binding activity in rat tissues. Metoprolol exhibited the highest affinity to specific binding sites of [125I]CYP in the rat heart, indicating the dominance of β1-adrenoceptors. β3-selective agonists (BRL37344 and CL316243) and antagonist (SR59230A) exhibited higher affinity to specific binding sites of [125I]CYP in the bladder than in the heart and lungs. Furthermore, the binding affinity of the β2-selective antagonist, ICI118551 was the highest in the bladder. The Bmax of specific [125]CYP binding in the bladder was significantly lower in WKY and SHR than in Wistar rats. The present study provides further evidence for the coexistence of β2-and β3-adrenoceptors in the rat bladder, and indicates that β-adrenoceptor density is lower in the bladders of WKY and SHR.