The Characterization of Beta-Adrenergic Receptor Subtypes of the Upper and Lower Renal Pelvis in Rabbits

Abstract

We characterized the beta-adrenergic receptors in the upper (pacemaker) and lower (nonpacemaker) regions of the rabbit renal pelvis, using radioligand binding techniques. [3H]Dihydroal-prenolol was the ligand used for determining the total density of beta-adrenergic receptors. The beta-1 and beta-2 subtypes of beta-adrenergic receptors were defined by inhibition of [3H]DHA binding by ICI 89,406, a beta-1 selective antagonist, and ICI 118,551, a beta-2 selective antagonist. Saturation studies with [3H]DHA showed that there was no significant difference in the equilibrium dissociation constant, KD, and the maximum number of binding sites Bmax, between the upper and lower renal pelvis. Although the inhibition constants of ICI 118,551 were smaller than those of ICI 89,406 in both the upper and lower pelvis, indicating a predominance of beta-2 receptors in both regions, the Ki values of ICI 118,551 were significantly greater in the upper than in lower pelvis. These data suggest that there are significant amounts of beta-adrenergic receptors in the rabbit renal pelvis without regional differences in the total density of beta receptors and that there is a greater proportion of beta-2 subtypes in the lower than in the upper renal pelvis.