Planta Med 2002; 68(8): 694-699
DOI: 10.1055/s-2002-33797
Paper
Pharmacology
© Georg Thieme Verlag Stuttgart · New York

Involvement of Nitric Oxide in the Mediation of the Hypotensive Action of the Essential Oil of Mentha × villosa in Normotensive Conscious Rats

Saad Lahlou1 , Pedro Jorge Caldas Magalhães2 , Ricardo Ferreira Lima Carneiro-Leão1 , José Henrique Leal-Cardoso3
  • 1Departamento de Fisiologia e Farmacologia, Universidade Federal de Pernambuco, Recife-PE, Brasil
  • 2Departamento de Fisiologia e Farmacologia, Universidade Federal do Ceará, Fortaleza-CE, Brasil
  • 3Departamento de Ciências Fisiológicas, Universidade Estadual do Ceará, Fortaleza-CE, Brasil
Further Information

Publication History

Received: November 23, 2001

Accepted: February 24, 2002

Publication Date:
09 September 2002 (online)

Abstract

Recently, we showed that intravenous (i.v.) treatment with the essential oil of Mentha × villosa (EOMV) in pentobarbitone-anaesthetised rats decreased blood pressure; the effect occurred independently of the presence of an operational central autonomic drive to the cardiovascular system. This finding suggested that the hypotensive activity of EOMV may result from its vasodilatory effects directly upon vascular smooth muscle. The present study examines this possibility and whether EOMV-induced hypotension is mediated, at least in part, by an endothelial L-arginine/nitric oxide pathway. In conscious rats, i.v. injections of bolus doses (1 to 20 mg/kg) of EOMV elicited immediate and dose-dependent decreases in mean aortic pressure (MAP) and heart rate (HR). Pretreatment with i.v. hexamethonium (30 mg/kg) reduced the EOMV-induced bradycardia without affecting the hypotension. However, i.v. pretreatment with the nitric oxide synthase inhibitor, N G-nitro-L-arginine methyl (L-NAME, 20 mg/kg), reduced partially, but significantly, the maximal percent decreases in MAP elicited by EOMV without affecting the bradycardia. In rat isolated thoracic aorta preparations, EOMV (1 - 130 μg/ml) induced a concentration-dependent reduction of potassium (60 mM)-induced contraction. This smooth muscle-relaxant activity of EOMV was significantly reduced by the incubation of endothelium-intact rings with L-NAME (20 μM), as evidenced by the significant enhancement in the IC50 for EOMV-induced reduction of potassium-induced contraction (133.8 ± 26.5 vs. 65.2 ± 8.2 μg/ml in the absence of L-NAME). Furthermore, the vasorelaxant effects of EOMV in endothelium-denuded aortic rings were also significantly reduced (IC50 = 109 ± 10 μg/ml), compared to those observed in segments with intact endothelium (IC50 = 61 ± 13 μg/ml). These results show that i.v. treatment with EOMV dose-dependently decreases blood pressure in conscious rats, and that this action is due to an active vascular relaxation rather than withdrawal of sympathetic tone. Released nitric oxide from vascular endothelial cells appears partially involved in the aortic relaxation induced by EOMV and in turn in the mediation of EOMV-induced hypotension. They further support the concept that EOMV-induced hypotension and bradycardia occurred independently.

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Dr. Saad. Lahlou

Departamento de Fisiologia e Farmacologia

Centro de Ciências Biológicas

Universidade Federal de Pernambuco

Cidade Universitária

50670-901, Recife

Pernambuco-PE

Brasil

Email: lahlou@npd.ufpe.br

Fax: +55 81-3271-8976