Cardiovascular effects of the essential oil of Mentha x villosa and its main constituent, piperitenone oxide, in normotensive anaesthetised rats: Role of the autonomic nervous system

Cardiovascular effects of intravenous (i.v.) treatment with the essential o il of Mentha x villosa (EOMV) were investigated in pentobarbitone-anaesthet ised rats. Additionally this study examines whether the major constituent o f EOMV, piperitenone oxide (PO), is the active principle mediating EOMV-ind uced changes in mean aortic pressure (MAP) and heart rate (HR) and whether the autonomic nervous system is involved in the mediation of these cardiova scular effects. Two samples of EOMV have been tested: one contained 62.32% of PO (sample 1) and the other contained a higher percent (95.87%) of PO (s ample 2). intravenous injections of bolus doses (1 to 20 mg/kg) of both sam ples of EOMV elicited immediate and dose-dependent decreases in MAP and HR. These cardiovascular responses were also observed following i.v. injection s of PO (1 to 20 mg/kg). However, maximal percent decreases in MAP and HR e licited by sample 2 of EOMV were significantly greater than those evoked by sample 1 of EOMV, while they were of the same order of magnitude as those elicited by PO. Pretreatment of rats with either bilateral vagotomy or Lv. methylatropine (1 mg/kg) did not modify significantly the hypotensive and b radycardic responses to EOMV. In contrast, pretreatment with i.v. hexametho nium (30 mg/kg) partially, but significantly, reduced the bradycardic effec ts of EOMV without affecting hypotension. The present study shows for the f irst time that L v. treatment with EOMV in pentobarbitone-anaesthetised rat s induces hypotensive and bradycardic effects, which appear mostly attribut ed to the actions of the major constituent of EOMV, PO. These cardiovascula r effects appear to be independent since EOMV-induced bradycardia appears d ependent upon the presence of an intact and functional sympathetic nerve dr ive to the heart, while EOMV-induced hypotension appears independent of the presence of an operational sympathetic nervous system. This suggests that hypotensive activity of EOMV may result from its vasodilatory effects direc tly upon vascular smooth muscle.