ABC | Volume 113, Nº5, November 2019

Original Article Bradycardic and Antiarrhythmic Effects of the D-Limonene in Rats Gildenisson Araújo do Nascimento, 1 Diego Santos de Souza, 1 B runo Santos Lima, 1 Carla Maria Lins de Vasconcelos, 1 Adriano Antunes de Souza Araújo, 1 Aimée Obolari Durço, 1 Lucindo José Quintans-Junior, 1 Jackson Roberto Guedes da Silva Almeida, 2 Aldeída Pereira Oliveira, 3 Valter Joviniano de Santana-Filho, 1 André Sales Barreto, 1 Márcio Roberto Viana dos Santos 1 Universidade Federal de Sergipe, 1 São Cristóvão, SE – Brazil Universidade Federal do Vale do São Franscisco, 2 Petrolina, PE – Brazil Universidade Federal do Piauí, 3 Teresina, PI – Brazil Mailing Address: Carla Maria Lins de Vasconcelos • Universidade Federal de Sergipe - Fisiologia - Av. Marechal Rondon, s/n. Postal Code: 49000-100, Rosa Elze, São Cristóvão, SE – Brazil E-mail: carlamlv@hotmail.com Manuscript received September 28, 2018, revised manuscript December 21, 2018, accepted Februry 13, 2018. DOI: 10.5935/abc.20190173 Abstract Background: D-limonene (DL) is a monoterpene and is the major component in the essential oil of citrus fruit. It presents antihyperglycemic and vasodilatation activities. Objectives: This study evaluated the cardiovascular effects and potential antiarrhythmic of DL in rats. Methods: Hemodynamic and electrocardiographic (ECG) parameters were measured in male Wistar rats, which under anesthesia had been cannulated in the abdominal aorta and lower vena cava and had electrodes subcutaneously implanted. In the in vitro approach, the heart was removed and perfused using the Langendorff technique. The significance level adopted was 5% (p < 0.05). Results: DL, in doses of 10, 20, and 40 mg/kg (i.v), produced intense and persistent bradycardia associated with hypotension. Bradycardia with prolonged QTc was observed in the ECG in vivo recording. In the in vivo model of arrhythmia induced by Bay K8644, DL (10 mg/kg) decreased the arrhythmia score from 15.33 ± 3.52 to 4.0 ± 2.64 u.a (p < 0.05, n = 4). In isolated perfused hearts, DL (10 -3 M) promoted significant reductions in heart rate (from228.6±8.5ms to 196.0±9.3 bpm; p < 0.05) and left ventricular development pressure (from 25.2 ± 3.4 to 5.9 ± 1.8 mmHg; n = 5, p < 0.05). Conclusions: DL produces bradycardia and antiarrhythmic activity in rat heart. (Arq Bras Cardiol. 2019; 113(5):925-932) Keywords: Rats; Limonene; Monoterpenes; Arrhythmias, Cardiac; Anti-Arrhythmia Agents; Bradycardia; Antioxidants. Introduction Despite the extensive research carried out on cardiac arrhythmias over the past decades, only a small number of antiarrhythmic drugs have emerged to add to the current therapeutic arsenal for this condition. Furthermore, "classical" antiarrhythmic drugs have serious efficacy and safety limitations and present several side effects. 1,2 In the search for therapeutic alternatives for arrhythmias, recent studies have screened naturally occurring chemical compounds aiming to evaluate their effects on cardiac parameters. For example, studies with the monoterpenes pulegone and geraniol showed a negative inotropism in the mammalian myocardium through blockage of the Ca 2+ and K + currents. 3-5 Most recently, Vasconcelos et al. 6 verified that citronellol and nerol present negative inotropism on the left atrium of guinea-pigs. D-limonene (DL) (Figure 1), is an alcoholic monoterpene and the major constituent of the essential oil extracted from citrus species such as lemon, lime and orange. 7 Previous studies have demonstrated that DL has low toxicity and presents antioxidant, 8,9 vasodilatation, 10,11 and antihypertensive proprieties. 12 The effect of DL on the heart has not yet been elucidated and investigations into its actionmechanismcan provide new insights about DL and the cardiovascular system. The current study, therefore, aimed to evaluate the potential antiarrhythmic effect de DL using both in vivo and ex vivo approaches. Methods Chemicals The chemicals usedwere: d-limonene (DL: purity: 97%), and S-(−)-Bay K8644, both purchased fromSigma Aldrich (Chemical CO, USA), and ketamine and xylazine (purchased from Sespo, São Paulo, Brazil). The DL stock solution was prepared using a saline/cremophor mixture (0.15% v/v), the S-(−)-Bay K8644 was diluted in methanol and the DL solution in distilled water. Stock solutions were preserved at 0°C and diluted with distilled water, if necessary. The vehicles (methanol or saline+cremophor) revealed no effect on the control preparations. Animals Thirty-six healthy rats ( Rattus norvegicus ), weighing between 250 and 350 g were obtained from colonies from the Physiology Department of the Federal University of Sergipe, Brazil. 925