Demonstration of alpha 1-adrenoceptors in rat nasal mucosa

3H-Prazosin was used to demonstrate alpha 1-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 pmol/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 alpha 1-adrenoceptors. Inhibition experiments with WB4101 indicated the presence of alpha 1a- (31 +/- 9%) and alpha 1b-adrenoceptor subtypes in the rat nasal mucosa. The order of potencies of agonists determined in competition experiments was (-)epinephrine greater than (+)epinephrine greater than (-)phenylephrine.