Effect of isomers of octopamine on in vitro reactivity of vascular smooth muscle of rats.

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 alpha-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 alpha-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.