Abstract

The Journal regrets that a printer's error occurred in the abstract of the following article in our March issue. The corrected abstract is reprinted in its entirety as follows:

Robert R. Ruffolo, Jr and James Waddell: "Aromatic and benzylic hydroxyl substitution of imidazolines and phenethylamines: Differences in activity at alpha-1 and alpha-2 adrenergic receptors," vol. 224, no. 3, March, 1983, pp. 559-566.

The effects of aromatic hydroxyl substitution and benzylic hydroxyl substitution of phenethylamines and imadazolines were investigated at alpha-1 and alpha-2 adrenergic receptors. For the alpha-2 adrenergic effects of both the phenethylamines and imidazolines, the cathechol moiety was an absolute requirement for agonist activity. Monohydroxyl substitution at either position 3 or position 4, or removal of all aromatic hydroxyl groups, abolished agonist activity at alpha-2 adrenergic receptors for both classes of compounds. Whereas aromatic hydroxyl substitution also was important for the alpha-1 adrenergic effects of both phenethylamines and imidazolines, this substitution appeared to be more critical for the imidazolines. For both classes of agonists, activity at alpha-1 adrenergic receptors declined with the following order of substitution: 3,4-dihydroxy > 3-hydroxy > 4-hydroxy > nonphenolic. Along this line of progression, a marked decrease in affinity was observed for the phenethylamines, whereas no change in relative efficacy (ability to activate receptor) was observed. Thus, while differences in potency did occur for the various hydroxy-substitued phenethylamines, these differences could be completely accounted for by decreases in affinity and all of these compounds still remained full agonists. In contrast, a decrease in both affinity and relative efficacy was observed for the imidazolines in following the same substitution pattern. We conclude, therefore, that for the phenethylamines, aromatic hydroxyl substitution affects affinity but not efficacy, whereas affinity and especially efficacy were altered by aromatic hydroxyl substitution of the imidazolines. Benzylic hydroxyl substitution had no effect on the relative efficacy of either the phenethylamines or imidazolines at alpha-1 adrenergic receptors. However, this substitution had marked, but opposite, effects on the affinities of the imidazolines and phenethylamines. Thus, β-hydroxyl substitution produced a dramatic increase in affinity of the phenethylamines, in accord with Easson-Stedman hypothesis, whereas the analogous hydroxyl substitution of the imidazolines decreased affinity, consistent with our previous observation that the Easson-Stedman hypothesis is not valid for the imidazolines. It is concluded that aromatic and benzylic hydroxyl substitutions have differential effects on the alpha-1 adrenergic activities of imidazolines and phenethylamines. These differences in the effects of aromatic and benzylic hydroxyl substitution highlight the differences in activity between the phenethylamines and imidazolines and suggest further that these two classes of agonists interact differently with alpha adrergic receptors.