Demonstration of Alpha₁-Adrenoceptors in Rat Nasal Mucosa

Abstract

³H-Prazosin was used to demonstrate Alpha¹-adrenoceptors in rat nasal mucosa. Specific binding is saturable and occurs to a homogeneous class of binding sites with high affinity (Kd=0.07 + 0.01 nmol/l and with a receptor density of 0.36 ± 0.02 pmo1/g tissue or 14 ± 1 fmol/mg protein. Kinetic experiments resulted in a Kd-value of 0.03 nmol/l. The binding is stereoselectively inhibited by epinephrine enantiomers. The antagonist prazosin inhibits ³H-Prazosin binding with high affinity, in contrast to yohimbine, classifying the binding sites as Alpha₁-adrenoceptors. Inhibition experiments with WB4101 indicated the presence of Alpha_{1 a}- (31 ± 9%) and Alpha_1b-adrenoceptor subtypes in the rat nasal mucosa. The order of potencies of agonists determined in competition experiments was (-)epinephrine > (+)epinephrine > (-)phenylephrine.