Role of cyclic AMP in hydrogen peroxide-induced potentiation of sympathetic neurotransmission in the bovine iris

Hydrogen peroxide (H2O2) has been shown to enhance electrically-evoked norepinephrine (NE) release from isolated, superfused bovine irides. Since stimulation of presynaptic adenylyl cyclase can potentiate sympathetic neurotransmission in several tissues, the present study considered the possibility that cyclic AMP may mediate the effects of H2O2 in the iris. Isolated bovine irides were prepared for analysis of field stimulation-induced [3H]NE release using the superfusion method. Both the diterpene activator of adenylyl cyclase, forskolin and the cyclic AMP-specific phosphodiesterase inhibitor, RO-201724 enhanced evoked [3H]NE overflow by 32%. On the other hand, inhibition of cyclic AMP-dependent protein kinase I/II by Rp-cAMPS attenuated field-stimulated [3H]NE release by 20%. Interestingly, both RO-201724 and Rp-cAMPS did not alter the enhancement of electrically-evoked [3H]NE overflow caused by submaximal concentrations of H2O2. We conclude that cyclic AMP may be involved in the pathway leading to NE release from sympathetic nerves in the bovine isolated iris. However, cyclic AMP may not be a mediator of H2O2-induced potentiation of sympathetic neurotransmission in this tissue.