Elsevier

Life Sciences

Volume 78, Issue 22, 25 April 2006, Pages 2615-2624
Life Sciences

Metformin reduces blood pressure and restores endothelial function in aorta of streptozotocin-induced diabetic rats

https://doi.org/10.1016/j.lfs.2005.10.020Get rights and content

Abstract

Effect of metformin treatment on blood pressure, endothelial function and oxidative stress in streptozotocin (STZ)-induced diabetes in rats was studied. In vitro effect of metformin on vascular reactivity to various agonist in the presence of metformin in untreated nondiabetic and STZ-diabetic rats were also studied. Sprague-Dawley rats were randomized into nondiabetic and STZ-diabetic groups. Rats were further randomized to receive metformin (150 mg/kg) or vehicle for 4 weeks.

Metformin treatment reduced blood pressure without having any significant effect on blood glucose level in STZ-diabetic rats. Enhanced phenylephrine (PE)-induced contraction and impaired acetylcholine (Ach)-induced relaxation in STZ-diabetic rats were restored to normal by metformin treatment. Enhanced Ach-induced relaxation in metformin-treated STZ-diabetic rats was blocked due to pretreatment with 100 μM of -nitro-l-arginine-methyl ester (l-NAME) or 10 μM of methylene blue but not 10 μM of indomethacin. Metformin treatment significantly increased antioxidant enzymes and reduced lipid peroxidation in STZ-diabetic rats. In vitro studies in aortic rings of untreated nondiabetic and STZ-diabetic rats showed that the presence of higher concentration of metformin (1 mM and 10 mM) significantly reduced PE-induced contraction and increased Ach-induced relaxation. Metformin per se relaxed precontracted aortic rings of untreated nondiabetic and STZ-diabetic rats in a dose-dependent manner. Pretreatment with l-NAME or removal of endothelium blocked metformin-induced relaxation at lower concentration (up to 30 μM) but not at higher concentration (above 30 μM). Metformin-induced relaxation was blocked in the presence of 1 mM of 4-aminopyridine, or 1 mM of tetraethylammonium but not in the presence of 100 μM of barium ion or 10 μM of glybenclamide. The restored endothelial function along with direct effect of metformin on aortic rings and reduced oxidative stress contributes to reduced blood pressure in STZ-diabetic rats. From the present study, it can be concluded that metformin administration to STZ-diabetic rats lowers blood pressure, and restores endothelial function.

Introduction

Cardiovascular disease is one of the leading causes of death in the western world and diabetes mellitus, which alters the vascular responsiveness to several vasoconstrictors and vasodilators, is a major factor underlying its development (Senses et al., 2001). Most of the complications in diabetes are due to increased serum glucose and increased generation of oxygen-derived free radicals, which lead to endothelium dysfunction. It has been shown that vessels from diabetic animals, exhibited abnormal endothelium-dependent vascular relaxation to acetylcholine (Oyama et al., 1986, Kamata et al., 1989).

Metformin belongs to bigunide insulin-sensitizing class of anti-diabetic drugs, widely used for the treatment of type 2 diabetes. The exact mechanisms of action of metformin, is poorly understood (Moller, 2001), but it includes suppression of endogenous glucose output by liver and increased sensitivity in skeletal muscle (Matthaei et al., 2000). Metformin lowers blood pressure in certain human patients (Landin et al., 1991, Giugliano et al., 1993) but not in others (Calle-Pascual et al., 1995, Gudbjo¨Rnsdottir et al., 1994, Campbell et al., 1987). Metformin lowers blood pressure in fructose fed rats (Verma et al., 1994), OLETF rats (Kosegawa et al., 1996), SHR (Bhalla et al., 1996, Muntzel et al., 1999) and insulin-resistant rats (Katakam et al., 2000). Metformin also has antioxidant activity which is independent of its effect of insulin activity (Faure et al., 1999). Recently Sartoretto et al. (2005) has reported that metformin increases nitric oxide activity but not expression and that it improves microvascular reactivity in n- STZ-diabetic rats (Type 2). There are no reports on effect of metformin on STZ-diabetic model (Type I) wherein free radical generation is one of the main causes of endothelial dysfunction (Kobayashi and Kamata, 1999, Zanetti et al., 2001). We have previously shown that administration of STZ causes a significant increase in blood pressure and oxidative stress (Majithiya et al., 2005). The current study investigates the effect of chronic metformin treatment on blood pressure, endothelial function and oxidative stress in streptozotocin-induced diabetic rats. Moreover, in vitro effects of metformin on aortic rings of STZ-diabetic and nondiabetic rats are also studied.

Section snippets

Drugs

Metformin hydrochloride and glybenclamide were obtained as a gift sample from Alembic Ltd, Baroda. Streptozotocin, phenylephrine, acetylcholine, -nitro-l-arginine-methyl ester (l-NAME), indomethacin, 4-aminopyridine, tetraethylammonium (TEA), epinephrine, 1,1,3,3,-tetra ethoxy propane, superoxide dismutase, catalase and glutathione standard were obtained form SIGMA, St. Louis, MO, USA. All other chemicals and reagents used in the study were of analytical grade. The composition of the Krebs

Blood glucose, body weight and systolic blood pressure

All streptozotocin-injected animals developed diabetes. The changes in blood glucose levels are shown in Table 1. Blood glucose levels remained unchanged in nondiabetic animals (N and N-MET groups). There was significant (p < 0.05) increase in blood glucose levels in streptozotocin injected animals. Metformin treatment did not have any significant effect on blood glucose level and body weight of diabetic rats (Table 1). There was a significant (p < 0.05) increase in systolic blood pressure in

Discussion

The blood pressure of 8-week STZ-diabetic rats was significantly higher as compared to nondiabetic control. The results are in concurrence with our previous study where the blood pressure was increased after 8 weeks of STZ administration and Ach-induced relaxation was impaired in aortic rings (Majithiya et al., 2005). Administration of metformin for 4 weeks restored the elevated blood pressure, reduced the enhanced contractibility to PE- and Ach-induced relaxation was restored. In

Acknowledgement

Financial assistance provided by The M.S. University of Baroda to Mr. Jayesh B Majithiya is highly acknowledged.

References (42)

  • J.L. Sartoretto et al.

    Metformin treatment restores the altered microvascular reactivity in neonatal streptozotocin-induced diabetic rats increasing NOS activity, but not NOS expression

    Life Science

    (2005)
  • S. Verma et al.

    Decreased vascular reactivity in metformin-treated fructose-hypertensive rats

    Metabolism

    (1996)
  • M.H. Zou et al.

    Activation of the AMP-activated protein kinase by the anti-diabetic drug metformin in vivo: role of mitochondrial reactive nitrogen species

    Journal of Biological Chemistry

    (2004)
  • H. Aebi

    Oxidoreductases acting on groups other than CHOH: catalase

  • A.L. Calle-Pascual et al.

    Comparison between acarbose, metformin, and insulin treatment in type 2 diabetic patients with secondary failure to sulfonylurea treatment

    Diabetes & Metabolism

    (1995)
  • I.W. Campbell et al.

    The effect of metformin on glycaemic control, intermediary metabolism and blood pressure in non-insulin-dependent diabetes mellitus

    Diabetes & Metabolism

    (1987)
  • P. Faure et al.

    An insulin sensitizer improves the free radical defense system potential and insulin sensitivity in high fructose-fed rats

    Diabetes

    (1999)
  • A. Gallo et al.

    Metformin prevents glucose-induced protein kinase c-β2 activation in human umbilical vein endothelial cells through an antioxidant mechanism

    Diabetes

    (2005)
  • D. Giugliano et al.

    Metformin improves glucose lipid metabolism, and reduces blood pressure in hypertensive, obese women

    Diabetes Care

    (1993)
  • R.J. Gryglewski et al.

    Superoxide anion is involved in the breakdown of endothelium-derived vascular relaxing factor

    Nature

    (1986)
  • S. Gudbjo¨Rnsdottir et al.

    The effect of metformin and insulin on sympathetic nerve activity, norepinephrine spillover and blood pressure in obese, insulin resistant, normoglycemic, hypertensive men

    Blood Pressure

    (1994)
  • Cited by (98)

    View all citing articles on Scopus
    View full text