Enhanced vascular reactivity of small mesenteric arteries from diabetic mice is associated with enhanced oxidative stress and cyclooxygenase products

1. Vascular reactivity to the alpha-adrenoceptor agonist phenylephrine (PE) was enhanced in small mesenteric arteries (SMA) from diabetic (db/db) mice under both high and low in vitro oxygen conditions. 2. Mechanical removal of the endothelium significantly attenuated the enhanced vascular reactivity of SMA from db/db mice. 3. Acute incubation of the SMA with sepiapterin, a precursor of tetrahydrobiopterin, and N(ω)-nitro L-arginine (L-NA), an inhibitor of nitric oxide (NO) synthase (NOS), resulted in no significant change in the enhanced vascular reactivity to PE in db/db mice. Endothelial nitric oxide synthase (eNOS) mRNA and protein levels in SMA were not different between db/+ and db/db mice. 4. Acute incubation of SMA with a combination of polyethylene glycol superoxide dismutase and catalase significantly reduced the enhanced contraction to PE in db/db mice. There were higher levels of malondialdehyde, a marker of lipid peroxidation and basal superoxide as measured by dihydroethidium staining, in SMA from db/db mice compared to db/+ mice. 5. Acute incubation with indomethacin, a nonselective inhibitor of cyclooxygenase, SQ 29548, a selective thromboxane receptor antagonist and furegrelate, a thromboxane synthesis inhibitor, significantly attenuated the enhanced contraction to PE in SMA from db/db mice. 6. This study demonstrates that the enhanced contractility of SMA from db/db mice to PE was endothelium dependent and involves elevated reactive oxygen species, cyclooxygenase activity and thromboxane synthesis, but not changes in the eNOS/NO pathway

Catalase has negligible inhibitory effects on endothelium-dependent relaxations in mouse isolated aorta and small mesenteric artery

1. The current study examined the hypothesis that endothelial production of hydrogen peroxide (H(2)O(2)) mediates relaxations to acetylcholine (ACh) in aorta and small mesenteric arteries (SMA) from mice. 2. Relaxations to ACh (0.01–10 μM) and H(2)O(2) (0.1–1000 μM) were produced in aorta and SMA isolated from wild-type C57BL/6 mice and type II diabetic mice (db/db). In SMA, relaxations to ACh were produced in the presence of N(ω)-nitro-L-arginine methyl ester (100 μM) and indomethacin (Indo, 10 μM). 3. 1-H[1,2,4]oxadiazolo[4,3-]quinoxalin-1-one (10 μM) significantly reduced ACh-induced relaxations in SMA, abolished responses in aorta, but had no effect on relaxations induced by H(2)O(2). Catalase (2500 U ml(−1)) abolished responses to H(2)O(2), but did not alter relaxations to ACh in the SMA and only caused a small rightward shift in responses to ACh in the aorta. 4. ACh-, but not H(2)O(2)-, mediated relaxations were significantly reduced by tetraethylammonium (10 mM), the combination of apamin (1 μM) and charybdotoxin (100 nM), and 25 mM potassium chloride (KCl). Higher KCl (60 mM) abolished relaxations to both ACh and H(2)O(2). Polyethylene glycolated superoxide dismutase (100 U ml(−1)), the catalase inhibitor 3-amino-1,2,4-triazole (3-AT, 50 mM) and treatment with the copper chelator diethyldithiolcarbamate (3 mM) did not affect relaxations to ACh. 5. H(2)O(2)-induced relaxations were endothelium-independent and were not affected by ethylene diamine tetraacetic acid (EDTA 0.067 mM), 4-aminopyridine (1 mM), ouabain (100 μM) and barium (30 μM), 3-AT or Indo. 6. Although the data from this study show that H(2)O(2) dilates vessels, they do not support the notion that H(2)O(2) mediates endothelium-dependent relaxations to ACh in either aorta or SMA from mice