Quantitative and Qualitative Analysis of the Pressor Effects of Levonordefrin

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Abstract
Levonordefrin, a common alternative to levoepinephrine as a vasoconstrictor in dental local anesthetic preparations, is usually used in 5-fold higher concentrations, and considered equivalent to epinephrine. Anesthetized dogs that had autonomic reflexes blocked by mecamylamine were used to reevaluate the cardiovascular actions of i.v. administered nordefrin with respect to epinephrine and norepinephrine over a 100-fold dose range (0.1-10.0 .mu.g/l kg). Epinephrine caused a significantly greater pressor effect than nordefrin at the highest dose studied; at low to moderate doses there was no significant difference between the two drugs. .alpha.-Adrenoceptor blockade by phentolamine attenuated the peak pressor effects of all 3 agents. The epinephrine dose-response curve was suppressed more than the norepinephrine and nordefrin, which did not significantly differ from each other. Nordefrin was indistinguishable qualitatively from norepinephrine because neither agent showed any evidence of .beta.2-adrenoceptor vasodilation as seen with epinephrine. Nordefrin evidently resembles norepinephrine rather than epinephrine in the receptor profile through which it produces its cardiovascular effects. The true potency difference between nordefrin and epinephrine with respect to pressor activity may be somewhat less than the 5-fold difference commonly assumed.

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