Abstract
Evidence from our laboratory shows that peroxides can enhance adrenergic neurosecretion from isolated human, rabbit, rat and bovine irides. In the present study, we examined the role of prejunctional autoreceptors in The effect caused by hydrogen peroxide (H2O2) on sympathetic neurotransmission. Hemi-irides were isolated from bovine eyes, preloaded with [3H]-norepinephrine ([3H]NE) and assayed for field-stimulated NE release using the superfusion method. Release of [3H]NE was elicited using 300 d.c. pulses applied at 80 mins. and 110 mins. after onset of superfusion. Clonidine (I nM - I μM) caused a concentration-related inhibition of evoked [3H]NE overflow which was antagonized by H2O2 (0.3 mM). Furthermore, potentiation of stimulated [3H]NE release induced by yohimbine (0.1 μM) was increased from 39±3% in the absence, to 143 ± 19% (n=6) in the presence of H2O2 (0.3 mM). We conclude that an effect on prejunctional α2-adrenoceptor activity may partially account for H2O2-mediated enhancement of sympathetic neurotransmission in the bovine iris.