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 neurotransmission in bovine irides and on the inhibitory effec t of this oxidant on norepinephrine (NE) release from human irides, in vitr o. Furthermore, we investigated the effect of 3-AT on H2O2-induced attenuat ion of contractile responses to carbachol in the bovine isolated irides. Is olated mammalian irides were prepared for studies of [H-3]NE release using the superfusion method and for contractile studies using isolated organ bat hs. At concentrations less than 100 muM, H2O2 had no significant effect on field-stimulated [H-3]NE release from bovine or human irides. In bovine iri des, 3-AT caused significant (P < 0.001) leftward shifts of concentration-r esponse curves to H2O2 (10 - 300 <mu>M). 3-AT also increased H2O2-induced a ttenuation of evoked [H-3]NE release from human isolated irides. Low concen trations of H2O2 (< 100 <mu>M) had no effect on carbachol contractions. How ever, 3-AT unmasked an inhibitory effect of low concentrations of H2O2 (3 - 100 muM) On carbachol-induced contractions. We conclude that inhibition of catalase causes both pre- and postjunctional responses of isolated mammali an irides to be more susceptible to oxidative stress induced by H2O2.