title: Mg2+-induced adenosine-receptor mediated relaxations in mesenteric vascular beds of diabetic rats.
abstract: Our previous studies showed that the magnesium Mg2+-induced relaxations were completely dependent on concentration of nitric oxide (NO) in non-diabetic rat mesenteric vascular beds, in diabetic rats other mechanisms may be involved. The present study was designed to determine the role of adenosine receptor in Mg2+-induced relaxation in streptozotocin (STZ)-induced diabetic rats vessels. Diabetes was induced by the intravenous injection of 60 mg/kg STZ. Eight weeks after diabetes induction, superior mesenteric arteries were isolated and perfused according to the McGregor method. Prepared vascular beds were constricted with phenylephrine to induce 70-75% of maximal constriction (0.001 M). Mg2+ at concentrations of 10(-4) to 10(-1) M were added into the medium and perfusion pressure was recorded. Theophylline (1 mM), and 3,7- dimethyl-1- propargylxanthine (0.01 μM) were added into medium 20 min before phenylephrine administration. In the presence of theophylline, vasorelaxation induced by high dose of Mg2+ (from 0.03 to 0.1 M) was totally suppressed. In presence of N(ω)-nitro-L-arginine methyl ester (L-NAME), the response of Mg2+ was completely inhibited at low dose of Mg2+. But, Mg2+-induced relaxation in the presence of adenosine A2a receptor blocker was significantly suppressed in high dose of Mg2+. Mg2+-induced relaxation in the presence of an A2a receptor blocker was not suppressed either by denudation of endothelium or presence of L-NAME. From the results of this study it may be concluded that Mg2+-induced relaxation at high concentrations is mediated by adenosine A2a receptors, but at low concentrations Mg2+-induced relaxation is dependent on NO.
authors.affiliation: Department of Biology, Faculty of Science, Arsanjan Azad University, Shiraz, Iran.
authors.forename: Roya A
authors.initials: RA
authors.lastname: Tavasoli
authors.forename: Nepton
authors.initials: N
authors.lastname: Soltani
authors.forename: Mansoor
authors.initials: M
authors.lastname: Keshavarz
authors.forename: Shahla
authors.initials: S
authors.lastname: Shorabipour
mesh_terms: D000818:Animals; D003921:Diabetes Mellitus, Experimental / Q000139:chemically induced / Q000503:physiopathology*; D003925:Diabetic Angiopathies / Q000503:physiopathology*; D004305:Dose-Response Relationship, Drug; D008274:Magnesium / Q000008:administration & dosage*; D008297:Male; D008638:Mesenteric Arteries / Q000187:drug effects* / Q000503:physiopathology*; D009569:Nitric Oxide / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D043705:Receptor, Adenosine A2A / Q000378:metabolism*; D013311:Streptozocin; D014655:Vascular Resistance / Q000187:drug effects
chemical_list: D043705:Receptor, Adenosine A2A; D009569:Nitric Oxide; D013311:Streptozocin; D008274:Magnesium