Increased β2-adrenoceptors in the superior cervical ganglia of genetically hypertensive rats

[¹²⁵I]Iodocyanopindolol binding sites were characterized by autoradiography in the superior cervical ganglia of Wistar-Kyoto (WKY) rats. A high concentration of (−)-[¹²⁵I]iodocyanopindolol binding sites, characterized as β-adrenoceptors by (−)-propranolol displacement, was distributed throughout the ganglia and in the postganglionic (internal carotid) nerve. ICI 118,551, a β₂-selective antagonist, displaced more than 85% of the binding sites, whereas CGP 20712A, a β₁-selective antagonist, displaced less than 10% of the binding sites, indicating that the β-adrenoceptors were primarily of the β₂-subtype. Emulsion autoradiography demonstrated that at least part of the binding sites were associated with principal ganglion cells. Unilateral deafferentation did not modify the number of binding sites in the superior cervical ganglia of WKY or spontaneously hypertensive rat (SHR). These results suggest that at least part of these receptors may correspond to prejunctional β₂-adrenoceptors originated in principal ganglion cells. The concentration of β₂-receptors was increased in the superior cervical ganglia of young and adult SHR when compared to age-matched WKY rats (49% and 39%, respectively). There were no differences in β₂-adrenoceptor number in the stellate ganglia of young and adult WKY and SHR. These results suggest that β₂-adrenoceptor stimulation may be selectively enhanced in some peripheral sympathetic ganglia in SHR and this could play a role in the development and maintenance of the increased symphatetic activity in this strain.