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 o il of Croton nepetaefolius (EOCN) were investigated in rats. Additionally, this study examined the importance of the autonomic nervous system in media tion of the EOCN-induced changes in mean aortic pressure (MAP) and heart ra te (HR), In both pentobarbitone-anaesthetised and conscious rats, i.v. bolu s injections of EOCN (1 to 50 mg/kg) elicited dose-dependent decreases in M AP and HR, Both decreases were of the same order of magnitude or duration, irrespective of whether the animal was under general anaesthesia. Pretreatm ent of anaesthetised rats with bilateral vagotomy reduced the magnitude of EOCN-induced bradycardia without affecting hypotension. Likewise, i.v. pret reatment of conscious rats with either methylatropine (1 mg/kg) or hexameth onium (30 mg/kg) significantly decreased the bradycardic effects of EOCN by the same order of magnitude. Neither compound influenced the hypotensive e ffects elicited by EOCN. This is the first physiological evidence that i.v. treatment with EOCN in either anaesthetised or conscious rats elicits hypo tension and bradycardia. EOCN-induced bradycardia appears dependent upon th e presence of an intact and functional parasympathetic nerve drive to the h eart. 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.