Muscarinic agonist properties involved in the hypotensive and vasorelaxant responses of rotundifolone in rats

The acute cardiovascular effects of rotundifolone (ROT), the major constituent (63.5%) of the essential oil of Mentha x villosa (OEMV), were tested in rats by using a combined (in vivo and in vitro) approach. ROT (1, 5, 10, 20 and 30 mg kg(-1) i.v.) induced a significant and dose-dependent hypotension and bradycardia in non-anaesthetized normotensive rats. The hypotensive effect was significantly attenuated by pre-treatment of the rats with atropine (2 mg kg(-1) i.v.) or L-NAME (20 mg kg(-1) i.v.). Furthermore, the bradycardic effect was abolished by atropine. In isolated rat atrial preparations, ROT (10, 100, 300 and 500 mug ml(-1)) produced concentration-related negative inotropic and chronotropic effects. in isolated intact aortic rings, increasing concentractions of ROT (0.3, 1, 10, 100, 300 and 500 mug ml(-1)) were able to antagonize the contractile effect of phenylephrine (I muM) (IC50 = 184 6 mug ml(-1)). The smooth muscle-relaxant activity of ROT was inhibited by either removal of vascular endothelium, atropine (1 muM), L-NAME (100 and 300 muM) or indomethacin (10 muM) (IC50 values = 235 +/- 7, 247 +/- 8, 387 +/- 21, 723 +/- 75 and 573 +/- 38 mug ml(-1), respectively). These results suggest that rotundifolone markedly lowers arterial pressure and heart rate in non-anaesthetized animals. The hypotensive action of roturidifolone can be a consequence of a decrease in heart rate and peripheral vascular resistance, probably due to a non-selective muscarinic receptor stimulation.