No abstract

Abstract. We have previously reported that peroxynitrite is involved in dysfunction of nitric oxide (NO)-mediated vasorelaxation in SHR/NDmcr-cp rats (SHR-cp), which display typical symptoms of metabolic syndrome. This study investigated whether peroxynitrite is actually generated in the vascular wall with angiotensin II-induced NADPH-oxidase activation, thus contributing to the dysfunction. In isolated mesenteric arteries of male 18-week-old SHR-cp, relaxations in response to acetylcholine and sodium nitroprusside were impaired compared with that in Wistar-Kyoto rats. This impaired relaxation was not restored by treatment with apocynin, an NADPH-oxidase inhibitor. Protein expression of endothelial NO synthase increased while that of soluble guanylyl cyclase (sGC) decreased in the artery. We observed increased production of superoxide anions and peroxynitrite from the artery and their inhibition by apocynin, and also increased contents of nitrotyrosine, a biomarker of peroxynitrite, in mesenteric arteries and angiotensin II in aortas. Long-term (8 weeks) administration of telmisartan, an angiotensin II type 1-receptor antagonist, prevented the impaired vasorelaxation, decreased sGC expression and increased nitrotyrosine content in mesenteric arteries. These findings suggest that in the vascular wall of SHR-cp, peroxynitrite is continually produced by the reaction of NO with NADPH oxidase-derived superoxide via angiotensin II and gradually denatures sGC protein, leading to vasorelaxation dysfunction.

Abstract. We investigated the effects of P2-receptor agonists on cell size, intracellular calcium levels ( ] i by 2meS-ATP were blocked by pyridoxalphosphate-6-azophenyl-2',4'-disulphonic acid (PPADS, P2Y 1 -antagonist), thapsigargin (Ca 2+-pump inhibitor), and U73122 (phospholipase C inhibitor). Furthermore, 2meS-ATP (P2Y 1 -receptor agonist) enhanced permeation of FD-4 through the endothelial cell monolayer. The 2meS-ATP-induced enhancement of the permeation was also prevented by PPADS, thapsigargin, and U73122. These results indicate that activation of P2Y receptors induces a decrease in cell size, an increase in [Ca 2+ ] i , and may participate in facilitating macromolecular permeability in HUVEC.

SHR/NDmcr-cp (SHR-cp) rats display typical symptoms and features of the metabolic syndrome. We previously reported that endothelium-dependent relaxation decreases in the thoracic aortas of SHR-cp rats, despite increased nitric oxide (NO) production from the endothelium. In the present study, to search for the reasons for this contradiction, we investigated whether vascular abnormality could be reduced by treatment of SHR-cp rats with antihypertensive drugs; a calcium channel blocker (amlodipine), an alpha 2 and imidazoline receptor agonist (moxonidine), and an angiotensin II type 1 (AT1) receptor antagonist (telmisartan). Telmisartan but not amlodipine and moxonidine ameliorated the impairment of relaxation in response to acetylcholine and the increased protein expression of endothelium NO synthase in thoracic aortas. All three drugs significantly lowered the blood pressure. Telmisartan decreased the serum levels of lipid peroxide and 8-hydroxy-2'-deoxyguanosine, oxidative stress markers, and also the aortic levels of the protein expression of gp91, a component of NADPH oxidase, and 3-nitrotyrosine, a biomarker of peroxynitrite. These findings suggest that NADPH oxidase-derived superoxide, probably produced due to stimulation of AT1 receptors, reacts with NO to form peroxynitrite, and consequently decreases active NO, leading to attenuation of endothelium-dependent relaxation. Angiotensin receptor antagonists may be effective for preventing endothelial dysfunction in metabolic syndrome.

1. Metabolic syndrome is an independent risk factor for cardiovascular disease. SHRSP.Z-Lepr(fa) /IzmDmcr (SHRSP fatty) rat, established as a new rat model of metabolic syndrome, spontaneously develops obesity, severe hypertension and shows hypertriglyceridaemia, hypercholesterolaemia and abnormal glucose tolerance. Using SHRSP fatty rats, we examined whether or not oxidative stress was correlated with vascular dysfunction in small and large calibre coronary arteries in ex vivo beating hearts, isolated mesenteric arteries and aortas in comparison with normal rats, Wistar-Kyoto rats (WKY). Vasodilation of coronary arteries was determined by microangiography of the Langendorff heart. 2. Compared with WKY, acetylcholine (ACh) and sodium nitroprusside (SNP)-induced relaxations were impaired in the coronary arteries of SHRSP fatty rats. The mesenteric arteries and aorta of SHRSP fatty rats showed impaired relaxation responses to ACh and SNP, decreased 3',5'-monophosphate (cGMP) production, and reduced soluble guanylyl cyclase protein expression. Superoxide release, angiotensin II and 3-nitrotyrosine contents were increased. 3. SHRSP fatty rats were orally administered olmesartan, an angiotensin II receptor type 1 (AT(1) ) antagonist, and amlodipine, a calcium channel blocker, at doses of 5 and 8mg/kg per day, respectively, for 8weeks. Both olmesartan and amlodipine reduced blood pressure, but only olmesartan prevented the development of abnormal vascular and biochemical parameters in the SHRSP fatty rats. 4. The results showed that in the SHRSP fatty rats, the impaired nitric oxide- and cGMP-mediated relaxation of vascular smooth muscle cells were linked to AT(1) receptor-induced oxidative-nitrative stress, which occurred concurrently with severe hypertension and metabolic abnormalities in vivo.