Abstract
In a previous study, we showed that hydrogen peroxide (H2O2) enhanced adrenergic neurosecretion in irides from several mammalian species presumably via a prejunctional action (Ohia et al., Exp. Eye Res. 59:Abs. No. 173, 1994). Purpose: To examine the effect of stress caused by various oxidants on norepinephrine (NE) release and membrane lipid peroxidation in the bovine isolated iris. Methods: Hemi-rides were isolated from bovine eyes and prepared for [3H]NE release assays using the superfusion method. For biochemical assays, lipid peroxidation was measured in iris membranes by determining their content of thiobarbituric acid reactive substances in the absence and presence of oxidants. Results: H2O2, cumene hydroperoxide (cuOOH) and t-butyl hydroperoxide (buOOH) caused a concentration-related enhancement of field stimulation-induced [3H]NE overflow with the following rank of potency: cuOOH>H2O2>buOOH. Potentiation of evoked [3H]NE release produced by submaximal concentrations of H2O2 (0.3 mM) and cuOOH (0.03 mM) was abolished by the antioxidant, melatonin (2 mM). Both H2O2 and cuOOH caused a concentration-dependent increase in lipid peroxidation over basal levels in isolated iris membranes. For instance, cuOOH (0.3 mM) increased lipid peroxidation (nmoles MDA/mg protein) from 2.99 ± 0.11 (n=10) to 8.16 ± 0.37 (n=7). Conclusion: We conclude that oxidants produce a specific enhancement of evoked NE release from sympathetic nerves in the bovine iris probably via an effect on membrane lipid peroxidation.