Role of catalase in pre- and postjunctional responses of mammalian irides to hydrogen peroxide

In the present study, we examined the effect of inhibition of catalase with 3-amino-triazole (3-AT) on hydrogen peroxide (H₂O₂)-induced enhancement of sympathetic neuro-transmission in bovine irides and on the inhibitory effect of this oxidant on norepinephrine (NE) release from human irides, in vitro. Furthermore, we investigated the effect of 3-AT on H₂O₂-induced attenuation of contractile responses to carbachol in the bovine isolated irides. Isolated mammalian irides were prepared for studies of [³H]NE release using the superfusion method and for contractile studies using isolated organ baths. At concentrations less than 100 μM, H₂O₂ had no significant effect on field-stimulated [³H]NE release from bovine or human irides. In bovine irides, 3-AT caused significant (P <0.001) leftward shifts of concentration-response curves to H₂O₂ (10 - 300 μM). 3-AT also increased H₂O₂-induced attenuation of evoked [³H]NE release from human isolated irides. Low concentrations of H₂O₂ (<100 μM) had no effect on carbachol contractions. However, 3-AT unmasked an inhibitory effect of low concentrations of H₂O₂ (3 - 100 μM) on carbachol-induced contractions. We conclude that inhibition of catalase causes both pre- and postjunctional responses of isolated mammalian irides to be more susceptible to oxidative stress induced by H₂O₂.