Effect of Acute Apelin Injection on Cardiac Muscle Performance in both Normal and Diabetic Rats

Background: Apelin is an adipokine originally identified as the endogenous ligand of the G protein coupled receptor APJ. Several studies have demonstrated that apelin and its receptor are involved in the regulation of cardiovascular function. Apelin was also found to have a positive inotropic effect in both rat and human hearts. However, this effect in case of cardiovascular diseases is controversial. Diabetes mellitus is one of the major risk factors for cardiovascular disease which is the leading cause of death in those patients. Aim: This study was designed to detect possible acute effects of in vivo apelin-13 injection on cardiac performance in both normal and diabetic state, with a trial to clarify possible involved mechanisms. Material \& methods: This study was conducted on 72 healthy, adult, male albino rats. The animals were divided equally into three main groups: Group I: Control group. Group II: Streptozotocin -induced diabetic non treated rats. Group III: Insulin treated diabetic rats. Experimental design: In the three groups we examined the effect of acute injection of apelin-13 (10 nmol /kg b.wt) alone or in the presence of propranolol (0.2mg/kg b.wt), verapamil (4.8mg/kg), benzamil HCL (Na/Ca+2 exchange (NCX) blocker) (10 nmol/kg), on cardiac muscle performance. Results: The present results demonstrated that apelin-13 administration significantly increased cardiac muscle performance (p<0.001) without any significant changes in heart rate, in all groups, as evidenced by the significant increase in (+dT(max)/t(max)) and (-dT(max)/t(r)). In addition, this increase was more significant in diabetic rats in comparison with that of both control and diabetic treated rats. Moreover, the observed effects are independent of the voltage-gated calcium channels or B-adrenergic receptors but appear to involve activation of the sacrolemmal Na++/Ca++ exchanger (NCX). Conclusion: apelin-13 exerted both positive inotropic and lusiotropic effects without affection of the heart rate in vivo, which was more significant in diabetic rats in comparison with that of both normal and insulin treated rats. Our results also suggested that this response to apelin involved activation of Na+-Ca+2 exchange channels (NCX). Therefore, the use of apelin may be investigated as a potential therapeutic target for diabetic cardiomyopathy. However, the impact of chronic administration requires further attention. {[}Mohammad I. Shehata, Mostafa H. Abdel-Salam, Dalia I. Abd Alaleem, and Hadeel A Al-Sherbiny. Effect of Acute Apelin Injection on Cardiac Muscle Performance in both Normal and Diabetic Rats. Life Sci J 2012; 9(2): 657-669]. (ISSN: 1097-8135). http://www.lifesciencesite.com. 99