Prejunctional alpha2-adrenoceptors and peroxide-induced potentiation of norepinephrine release from the bovine iris.
Peroxides can enhance field-stimulated [3H]norepinephrine ([3H]NE) release in isolated irides from several mammalian species. In the present study, we investigated the role of prejunctional alpha2-adrenoceptors in peroxide-induced potentiation of sympathetic neurotransmission in bovine isolated irides. Isolated hemi-irides were incubated in a Krebs buffered-solution containing [3H]NE and prepared for studies of neurotransmitter release using the superfusion method. Alpha2-adrenoceptor agonists, oxymetazoline, UK-14304 and clonidine inhibited field-stimulated [3H]NE overflow without affecting basal tritium efflux. Pretreatment of tissues with H2O2 (300 microM) had no effect on inhibition of evoked [3H]NE release caused by the alpha2-adrenergic agonists. However, H2O2 (300 microM) caused significant (P < 0.01) leftward shifts of excitatory concentration-response curves to yohimbine (10 nM-1 microM). In contrast, yohimbine (1 microM) did not prevent the enhancement of evoked [3H]NE overflow induced by H2O2 (300 microM). In conclusion, excitatory effects of peroxides on sympathetic neurotransmission in bovine irides are not mediated by prejunctional alpha2-adrenoceptors.
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Department of Pharmaceutical and Administrative Sciences, Creighton University Health Sciences Center, Omaha, NE 68178, USA.
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D000320:Adrenergic Fibers / Q000187:drug effects / Q000502:physiology; D058647:Adrenergic alpha-2 Receptor Agonists; D058669:Adrenergic alpha-2 Receptor Antagonists; D000818:Animals; D000068438:Brimonidine Tartrate; D002417:Cattle; D003000:Clonidine / Q000494:pharmacology; D046508:Culture Techniques; D006861:Hydrogen Peroxide / Q000494:pharmacology*; D007498:Iris / Q000187:drug effects* / Q000378:metabolism*; D009451:Neuroeffector Junction; D009638:Norepinephrine / Q000032:analysis / Q000378:metabolism*; D010109:Oxymetazoline / Q000494:pharmacology; D010477:Perfusion; D011810:Quinoxalines / Q000494:pharmacology; D017382:Reactive Oxygen Species / Q000502:physiology; D018341:Receptors, Adrenergic, alpha-2 / Q000502:physiology; D009435:Synaptic Transmission / Q000187:drug effects; D014316:Tritium; D015016:Yohimbine / Q000494:pharmacology
D058647:Adrenergic alpha-2 Receptor Agonists; D058669:Adrenergic alpha-2 Receptor Antagonists; D011810:Quinoxalines; D017382:Reactive Oxygen Species; D018341:Receptors, Adrenergic, alpha-2; D014316:Tritium; D015016:Yohimbine; D000068438:Brimonidine Tartrate; D010109:Oxymetazoline; D006861:Hydrogen Peroxide; D003000:Clonidine; D009638:Norepinephrine