The effects of epinephrine in local anesthetics on plasma catecholamine and hemodynamic responses.

In order to clarify the influence of epinephrine in local anesthetics on endogenous epinephrine, we examined the concentration of plasma catecholamines (epinephrine and norepinephrine) and hemodynamics by administering 4 ml of 2% lidocaine containing different concentrations of epinephrine. Forty-three healthy adult male volunteers were divided into five groups according to epinephrine concentration: 0-microg (group I), 10-microg (group II), 20-microg (group III), 40-microg (group IV), and 50-microg (group V). The parameters were examined immediately, and at 1, 2, 3, 4, 5, 10, 15, and 20 min after the injection. In groups II, III, IV, and V, the plasma epinephrine concentration was elevated to peak at 5 min after the injection, after which it started to decline. The amount of increase in the plasma epinephrine concentration at 5 min showed a highly positive correlation with the amount of epinephrine added to the local anesthetic in groups II, III, and IV. In group V the plasma epinephrine concentration showed a marked increase as compared to the baseline level. Plasma norepinephrine concentrations were found to be significantly elevated at 15 and 20 min in group V. A decrease in systolic blood pressure was observed at 4 and 5 min in group II. A decrease in diastolic blood pressure was observed at 5 min in group II; at 3, 4, and 5 min in group IV; and at 2, 3, 4, and 5 min in group V. Heart rate revealed no significant differences from baseline level in any of the groups and there were no significant differences among the groups. It is suggested that exogenous epinephrine added to a local anesthetic may stimulate the presynaptic beta2 receptors on sympathetic nerve endings and on the adrenomedulla, and accelerate the release of endogenous epinephrine.