409 Gen. Physiol. Biophys. (2012), 31, 409–413 doi:10.4149/gpb_2012_050 Mg 2+ -induced adenosine-receptor mediated relaxations in mesenteric vascular beds of diabetic rats Roya Amiri Tavasoli 1 , Nepton Soltani 2 , Mansoor Keshavarz 3 and Shahla Shorabipour 2 1 Department of Biology, Faculty of Science, Arsanjan Azad University, Shiraz, Iran 2 Department of Physiology, Faculty of Medicine, and Research Center for Molecular Medicine, Hormozgan University of Medical Science, Bandar Abbas, Iran 3 Department of Physiology, Faculty of Medicine, Tehran University of Medical Science, Tehran, Iran Abstract. Our previous studies showed that the magnesium Mg 2+ -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. Te present study was de- signed to determine the role of adenosine receptor in Mg 2+ -induced relaxation in streptozotocin (STZ)-induced diabetic rats vessels. Diabetes was induced by the intravenous injection of 60 mg/kg STZ. Eight weeks afer 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). Mg 2+ at concentrations of 10 –4 to 10 –1 M were added into the medium and perfusion pressure was recorded. Teophylline (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 Mg 2+ (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 Mg 2+ was completely inhibited at low dose of Mg 2+ . But, Mg 2+ -induced relaxation in the presence of adenosine A2a receptor blocker was significantly suppressed in high dose of Mg 2+ . Mg 2+ -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 Mg 2+ -induced relaxation at high concentrations is mediated by adenosine A2a receptors, but at low concentrations Mg 2+ -induced relaxation is dependent on NO. Key words: Diabetes — Magnesium — Adenosine A2a receptor — Nitric oxide — Mesenteric bed Correspondence to: Nepton Soltani, Department of Physiol- ogy, Faculty of Medicine, and Research Center for Molecular Medicine, Hormozgan University of Medical Science, Bandar Abbas, Iran E-mail: neptun.soltani@gmail.com nsoltani@hums.ac.ir Introduction Diabetes mellitus is a metabolic disorder resulting from defect in insulin secretion, insulin action or both (Bon- ner 2000). Despite the fact that it has a high prevalence, morbidity and mortality throughout the world, it is re- garded as a non-curable but controllable disease. Vascular disease is one of the complicating features of diabetes mellitus (Kamata and Kondoh 1996; Panus et al. 2003). The prevalence of hypertension in diabetic population is almost twice as compared to non-diabetic general popu- lation (Garcia et al. 1974; Jarrett 1989). Hypertension is also considered to be an independent risk factor for car- diovascular mortality in patients with diabetes (Ozcelikay et al. 2000). It has been suggested that alterations in the reactivity of blood vessels to neurotransmitters and cir- culating hormones are responsible for the cardiovascular complications of diabetes (Christlieb et al. 1976; Ozcelikay et al. 2000). Our previous studies showed that Mg 2+ could decrease the basal tone and phenylephrine-induced contraction in