Increased activity of H2O2 in aorta isolated from chronically streptozotocin-diabetic rats: effects of antioxidant enzymes and enzymes inhibitors.
The effects of hydrogen peroxide (H2O2, 1 nM-5 mM) on the tone of the rings of aorta precontracted with phenylephrine (PE) were studied in 4-5 months streptozotocin (STZ)-diabetic rats and their age-matched controls. H2O2 induced brief contraction before relaxation in endothelium-containing rings that was more pronounced in diabetic rats. Removal of the endothelium or pretreatment of rings with N(G)-nitro-L-arginine methyl ester (L-NAME, 100 microM) abolished H2O2-induced immediate and transient increase in tone, but preincubation with indomethacin (10 microM) had no effect on contractions induced by H2O2 in both group of animals. Pretreatment with L-NAME or indomethacin as well as absence of endothelium produced an inhibition of H2O2-induced relaxation that was more pronounced in diabetic rings. Chronically STZ-diabetes resulted in a significant increase in H2O2-induced maximum relaxation that was largely endothelium-dependent. Decreased sensitivity (pD2) of diabetic vessels to vasorelaxant action of H2O2 was normalized by superoxide dismutase (SOD, 80 U/ml). Pretreatment with SOD had no effect on H2O2-induced maximum relaxations in both group of animals but led to an increase in H2O2-induced contractions in control rats. When the rings pretreated with diethyldithiocarbamate (DETCA, 5 mM), H2O2 produced only contraction in control rats, and H2O2-induced relaxations were markedly depressed in diabetic rats. H2O2 did not affect the tone of intact or endothelium-denuded rings in the presence of catalase (2000 U/ml). Aminotriazole (AT, 10 mM) failed to affect H2O2-induced contractions or relaxations in all rings. Our observations suggest that increased production of oxygen-derived free radicals (OFRs) in diabetic state leads to a decrease in SOD activity resulting an increase in endogenous superoxide anions (O2*-), that is limited cytotoxic actions, and an increase in catalase activity resulting a decrease in both H2O2 concentrations and the production of harmful hydroxyl radical (*OH) in diabetic aorta in long-term. Present results indicate that increased vascular activity of H2O2 may be an important factor in the development of vascular disorders associated with chronically diabetes mellitus. Enhanced formation of *OH, that is a product of exogenous H2O2 and excess O2*, seems to be contribute to increased relaxations to exogenously added H2O2 in chronically diabetic vessels.
Karasu
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Ankara University, Faculty of Pharmacy, Department of Pharmacology, Tandoğan, Turkey. karasu@pharmacy.ankara.edu.tr
D000640:Amitrole / Q000494:pharmacology; D000818:Animals; D000975:Antioxidants / Q000494:pharmacology*; D001011:Aorta / Q000187:drug effects / Q000503:physiopathology*; D002374:Catalase; D016861:Cyclooxygenase Inhibitors / Q000494:pharmacology; D003921:Diabetes Mellitus, Experimental / Q000503:physiopathology*; D004730:Endothelium, Vascular / Q000187:drug effects / Q000503:physiopathology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004958:Estradiol / Q000031:analogs & derivatives / Q000494:pharmacology; D006861:Hydrogen Peroxide / Q000494:pharmacology*; D007213:Indomethacin / Q000494:pharmacology; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects; D009126:Muscle Relaxation / Q000187:drug effects; D019331:NG-Nitroarginine Methyl Ester / Q000494:pharmacology; D016877:Oxidants / Q000494:pharmacology*; D010656:Phenylephrine / Q000494:pharmacology; D051381:Rats; D013311:Streptozocin; D013482:Superoxide Dismutase; D014662:Vasoconstrictor Agents / Q000494:pharmacology
D000975:Antioxidants; D016861:Cyclooxygenase Inhibitors; D004791:Enzyme Inhibitors; D016877:Oxidants; D014662:Vasoconstrictor Agents; D010656:Phenylephrine; D004958:Estradiol; D013311:Streptozocin; C073106:3,17-diacetoxyestra-1,3,5(10)-trien-2-carboxylic acid; D006861:Hydrogen Peroxide; D002374:Catalase; D013482:Superoxide Dismutase; D019331:NG-Nitroarginine Methyl Ester; D007213:Indomethacin; D000640:Amitrole