EPINEPHRINE POTENTIATION IN ISOLATED RABBIT AORTIC STRIPS

¹ Department of Pharmacology, University of Mississippi Medical Center, Jackson, Mississippi

A unique type of potentiation to low doses of epinephrine in isolated rabbit aortic strips is described. This potentiation has the following characteristics: 1) Potentiation of low doses of epinephrine (10^-l0-10^-9 M) develops after pretreatment with high doses of epinephrine (10^-7-10^-5 M). 2) Time (120 min) is required between the first and second application of epinephrine for full development of this potentiation. 3) Potentiation to low concentrations of epinephrine or norepinephrine is not observed in strips pretreated with high doses of norepinephrine. 4) Potentiation can be abolished by treating sensitized strips with high doses of norepinephrine but not other contractile agents such as isoproterenol, angiotensin or tyramine. 5) Reserpine-pretreated preparations do not develop potentiation to epinephrine unless pretreated with high doses of norepinephrine. 6) Potentiation to low concentrations of epinephrine can also be produced by repeated exposures to tyramine in normal preparations but not in reserpine-pretreated preparations. Although the mechanism of this effect is not clear, the possibility is suggested that it is related to a displacement or translocation of norepinephrine and the subsequent production of a metabolite or change resulting in potentiation.