Adrenergic Activity of Ortho-, Meta-, and Para-Octopamine

DL-o-, m-, and p-octopamine were tested for β- and α-adrenergic activity in rats. When compared to DL-isoproterenol, a β-adrenergic agonist, all three isomers failed to show significant β-adrenergic activity as assessed by initiation of thirst and by increase in tail skin temperature. All three isomers increased mean blood pressure in pentolinium-blocked rats. Of the three isomers, m-octopamine possessed the greatest α-adrenergic activity. When the responses were compared with those induced by L-norepinephrine, the order of activities was: 1:0.01:0.0005:0.00007 for norepinephrine, m- p- and σ-octopamine, respectively. Thus, DL-m-octopamine has about l/l00th the α-adrenergic activity of L-norepinephrine.