title: Calcium-dependent mechanisms mediate the vasorelaxant effects of Tridax procumbens (Lin) aqueous leaf extract in rat aortic ring.
abstract: BACKGROUND
  Tridax procumbens leaf extract has a folk reputation as an antihypertensive agent in Nigeria. Evidence suggests that it has a relaxant effect on smooth muscles. The present study was designed to investigate the role of calcium in the vasorelaxant effect of this extract.
  
  
  METHODS
  Concentration-response studies with noradrenaline (NA), KCl and CaCl2 were carried out in rat aortic rings with and without the extract in physiological salt solution (PSS) (n=6 each). Also, the role of intracellular calcium mobilization was studied by measuring the phasic response to NA in Ca2+-free N,N-ethylene glycol tetraacetic acid (EGTA) PSS (n=6).
  
  
  RESULTS
  The results showed that the contractile responses to either NA or KCl were attenuated (p<0.05) in the presence of the extract. Also, the extract attenuated the contractile response to CaCl2 in the presence of NA or KCl (p<0.05) in the Ca2+-free EGTA PSS, while the phasic response to NA was significantly (p<0.05) diminished.
  
  
  CONCLUSIONS
  These results suggest that the vasorelaxant effect of T. procumbens leaf extract may be mediated by a non-specific, non-competitive inhibition of Ca2+ influx as well as by inhibition of Ca2+ mobilization from intracellular stores. This implies that it may contain vasorelaxant agents that may have calcium antagonistic potential.
authors.forename: Hussein M
authors.initials: HM
authors.lastname: Salahdeen
authors.forename: Gbolahan O
authors.initials: GO
authors.lastname: Idowu
authors.forename: Omoniyi K
authors.initials: OK
authors.lastname: Yemitan
authors.forename: Babatunde A
authors.initials: BA
authors.lastname: Murtala
authors.forename: Abdul-Rasak A
authors.initials: AR
authors.lastname: Alada
mesh_terms: D000818:Animals; D001013:Aorta, Thoracic / Q000187:drug effects* / Q000378:metabolism; D019659:Asteraceae / Q000737:chemistry*; D002118:Calcium / Q000378:metabolism; D002122:Calcium Chloride / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D005260:Female; D066298:In Vitro Techniques; D008297:Male; D016488:Medicine, African Traditional; D009119:Muscle Contraction / Q000187:drug effects; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000378:metabolism; D010936:Plant Extracts / Q000302:isolation & purification / Q000494:pharmacology*; D018515:Plant Leaves / Q000737:chemistry; D017208:Rats, Wistar; D014662:Vasoconstrictor Agents / Q000494:pharmacology; D014664:Vasodilation / Q000187:drug effects*; D014665:Vasodilator Agents / Q000302:isolation & purification / Q000494:pharmacology*
chemical_list: D010936:Plant Extracts; D014662:Vasoconstrictor Agents; D014665:Vasodilator Agents; D002122:Calcium Chloride; D002118:Calcium