Cardiovascular effects of the essential oil of Croton nepetaefolius in rats:: Role of the autonomic nervous system

Cardiovascular effects of intravenous (i.v.) treatment with the essential oil of Croton nepetaefolius (EOCN) were investigated in rats. Additionally, this study examined the importance of the autonomic nervous system in mediation of the EOCN-induced changes in mean aortic pressure (MAP) and heart rate (HR), In both pentobarbitone-anaesthetised and conscious rats, i.v. bolus injections of EOCN (1 to 50 mg/kg) elicited dose-dependent decreases in MAP and HR, Both decreases were of the same order of magnitude or duration, irrespective of whether the animal was under general anaesthesia. Pretreatment of anaesthetised rats with bilateral vagotomy reduced the magnitude of EOCN-induced bradycardia without affecting hypotension. Likewise, i.v. pretreatment of conscious rats with either methylatropine (1 mg/kg) or hexamethonium (30 mg/kg) significantly decreased the bradycardic effects of EOCN by the same order of magnitude. Neither compound influenced the hypotensive effects elicited by EOCN. This is the first physiological evidence that i.v. treatment with EOCN in either anaesthetised or conscious rats elicits hypotension and bradycardia. EOCN-induced bradycardia appears dependent upon the presence of an intact and functional parasympathetic nerve drive to the heart. However, EOCN-induced hypotension appears independent of the presence of an operational sympathetic nervous system. This suggests that EOCN may be a direct vasorelaxant agent.