Effect of Isomers of Octopamine on in vitroReactivity of Vascular Smooth Muscle of Rats

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Abstract
The vascular reactivity to DL-ortho-, meta-, and para-octopamine was tested in vitro in aortic smooth muscle of the rat. When reactivities were compared on a molar basis with L-phenylephrine, an α-adrenergic agonist, the potencies of the three isomers were: 0.7500, 0.0075 and 0.0038 times that of phenylephrine for the m-, p- and o-isomer, respectively. Thus, of the three isomers, DL-m-octopamine had the greatest α-adrenergic activity in vitro as it did in vivo in earlier studies. Additional studies showed L-phenylephrine to induce about one-third the vascular response induced by L-norepinephrine.