The Open Physiology Journal, 2009, 2, 14-17 14 1874-3609/09 2009 Bentham Open Open Access Effect of Intra-Venous Versus Intra-Arterial Leptin Infusion on Blood Pressure and Heart Rate Khalid F. Talafih 1 , Mohamad Mousa J. Mohamad 1 , Mukhallad A. Mohammad *,1 and Zeyad J. El-Akawi 2 1 Department of Physiology/Faculty of Medicine, Jordan University of Science and Technology, Irbid 22110, Jordan; 2 Department of Biochemistry and Molecular Biology/Faculty of Medicine, Jordan University of Science and Technol- ogy, Irbid 22110, Jordan Abstract: Objectives: In this study the effects of different Leptin concentrations on the blood pressure and heart rate in vivo in anesthetized rabbits were studied. Methods: Sixty Rabbits were divided into two groups, first group received Leptin intra-venously and other group received Leptin intra-arterially. Blood pressure and heart rate in were recorded before and after administration of Leptin. Results: A significant increase in mean arterial blood pressure (MABP) was seen after an intra-arterial injection of 3, 5 and 7 g/kg of Leptin. This increase in MABP was monitored for different durations 10, 20 and 30 minutes after the infu- sion of each Leptin concentrations. The trend of the increase in MABP with time was demonstrated with all three concen- trations. Intra-venous infusion of Leptin caused a significant decrease in MABP after 10 minutes as well as after 20 and 30 minutes, with all three concentrations (3, 5, and 7 μg/Kg). Heart rate (HR) was not changed significantly at the end of 30 min of infusion. Conclusion: this in vivo study demonstrated that intra-venous Leptin infusion has a different effect on the MABP com- pared with intra-arterial infusion and this difference might be due to the site of action of Leptin. Keywords: Leptin, cardiovascular, blood pressure, heart rate. INTRODUCTION Leptin is a polypeptide hormone synthesized in white adipose tissues and encoded by the ob gene [1]. It plays an important role in the energy balance. This Leptin effect is taking place by its interaction with specific hypothalamic receptors affecting appetite and satiety centers of the brain in a feedback loop [2-4]. Administration of Leptin to mice causes a decrease in food intake, weight loss and an increase in energy expenditure [5-7]. Leptin effects on the cardiovas- cular system include elevation in blood pressure [8] and vasodilatation [9]. For example, the increase in blood pres- sure might be caused by increasing the heart rate and vaso- constriction through the sympathetic effect of Leptin [8,10- 12]. In contrast, the vasodilatation effect of Leptin modu- lated through a local mechanism involving nitric oxide (NO) release [9,13-15]. Recent study by Mohamad et al., on the effect of Leptin on isolated rat mesenteric arteries demon- strated that, the administration of Leptin induces relaxation of vascular smooth muscle through an endothelium- dependent release of nitric oxide (EDNO). In the same study, they also showed that the vascular effect was abolished by *Address correspondence to this author at the Department of Physiol- ogy/Faculty of Medicine, Jordan University of Science and Technology, Irbid 22110, Jordan; Tel: Office: (02) – 7201000: Ext: (23671). Cell: (079) - 5158960; Fax: 962-2-7201064; E-mail: mukmoh@just.edu.jo administration of NO synthase blocker L-nitol-L-arginine methyl ester (L-NAME) [16]. A significant correlation be- tween blood pressure and plasma Leptin concentration in patients with essential hypertension was demonstrated [17]. It was also demonstrated that high plasma Leptin concentra- tion might be involved in the development of cardiovascular diseases including myocardial infarction in obese people [18]. In animal module, Shek et al. had shown that chronic administration of high Leptin both intra-arterially or intra- venously causes increased in blood pressure and heart rate [19]. The aim of this study was to find the effect of different Leptin concentrations on the cardiovascular system (heart rate and blood pressure) in vivo in anesthetized rabbits. Us- ing different concentrations of Leptin infused through the veins and arteries. METHODS This study was approved by scientific research commit- tee at Jordan University of Science and Technology and ethical approval by medical faculty research committee. Sixty New Zealand white adult rabbits of either sex, weight ranged between 1.5 and 2.5Kg were used in this study. Rab- bits were divided into two groups (A and B), each group was consisting of thirty rabbits. Leptin was administered intra- arterially in rabbits of group A (three subgroups;A1,A2,A3 each consists of 10 animals and each one received different leptin concentration) while it infused intra-venously in rab-