Effects of ascorbic acid and EDTA on vascular concentration-response to catecholamines

Concentration-response curves are often used as indicators of vascular reactivity and receptor sensitivity. Some investigators use ethylenediaminetetraacetate (EDTA) or ascorbic acid (ASC) to prevent catecholamine oxidation but many others do not. This difference may affect estimates of reactivity. We tested the effect of EDTA or ASC on contractile responses of hamster cremaster arterioles and rat aortic strips to epinephrine (EPI) or norepinephrine (NOR). Comparable contractile responses were elicited by lower EPI or NOR concentrations in the presence than in the absence of EDTA or ASC. Individual responses to EPI or NOR were maintained in the presence of EDTA or ASC, but rapidly declined if neither were present. Rapidly prepared and administered solutions of EPI or NOR elicited similar initial responses in the presence or absence of EDTA or ASC. However, catecholamine solutions prepared without these compounds lose effectiveness within minutes. We conclude that oxidation of EPI and NOR reduces apparent vascular reactivity and that EDTA or ASC prevents or delays the reduction.