Effects of ephedrine and its analogs onβ-adrenoceptors of rat lung cell membrane1

The affinities of l-ephedrine (l-Eph), d-pseudoephedrine (d-pseudo-Eph), l-methylephedrine (l-Me-Eph) and d-pseudonorephedrine (d-pseudo-nor-Eph) toβ-adrenoceptors were investigated on isolated rat lung cell membranes by ligand binding assay. All the compounds competed with the binding of [3H]dihydroalprenolol to the rat lung cell membrane preparations. The orders of affinity toβ-adrenoceptors were: l-Eph>d-pseudo-nor-Eph >d-pseudo-Eph>l-Me-Eph. The action of l-Eph to activate the adenyl cyclase (AC) was greater than those of d-pseudo-Eph and l-Me-Eph, which appeared to be consistent with the orders of affinity toβ-adrenoceptors. The facts that d-pseudo-nor-Eph has no effect on AC activity and antagonizes the stimulating action of isoproterenol on AC activity suggest that d-pseudo-nor-Eph is aβ-adrenoceptor blockader.