title: Possible mechanisms of action of the hypotensive effect of Annona muricata (soursop) in normotensive Sprague-Dawley rats.
abstract: BACKGROUND
  Annona muricata Linn (Annonaceae) (soursop) is a food plant reported to have antihypertensive properties.
  
  
  OBJECTIVE
  We investigated the blood pressure reducing effect of its aqueous leaf extract and the possible mechanisms that may be responsible.
  
  
  METHODS
  Intravenous administration of an aqueous leaf extract (9.17-48.5 mg/kg) of A. muricata on the mean arterial pressure and heart rate were recorded invasively on anaesthetized, normotensive Sprague-Dawley rats. Contractile responses of rat aortic rings to the extract (0.5-4.0 mg/mL) were studied using standard organ bath techniques.
  
  
  RESULTS
  A. muricata (9.17-48.5 mg/kg) caused significant (p < 0.05) dose-dependent reduction in blood pressure without affecting the heart rates. The hypotensive effects were unaffected by atropine (2 mg/kg), mepyramine (5 mg/kg), propranolol (1 mg/kg) and L-NAME (5 mg/kg). A. muricata leaf aqueous extract significantly (p < 0.05) relaxed phenylephrine (10(-9)-10(-4) M) and 80 mM KCl induced contractions in endothelium intact and denuded aortic rings; and caused a significant (p < 0.05) rightward shift of the Ca(2+) dose response curves in Ca(2+)-free Kreb's solution containing 0.1 mM EGTA.
  
  
  CONCLUSIONS
  The hypotensive effects of A. muricata are not mediated through muscarinic, histaminergic, adrenergic and nitric oxide pathways, but through peripheral mechanisms involving antagonism of Ca(2+).
authors.affiliation: Department of Basic Medical Sciences (Physiology Section), The University of the West Indies, Mona, Kingston 7, Jamaica. chukwuemeka.nwokocha@uwimona.edu.jm
authors.forename: Chukwuemeka R
authors.initials: CR
authors.lastname: Nwokocha
authors.forename: Daniel U
authors.initials: DU
authors.lastname: Owu
authors.forename: Angeline
authors.initials: A
authors.lastname: Gordon
authors.forename: Karen
authors.initials: K
authors.lastname: Thaxter
authors.forename: Garsha
authors.initials: G
authors.lastname: McCalla
authors.forename: Raymond I
authors.initials: RI
authors.lastname: Ozolua
authors.forename: Lauriann
authors.initials: L
authors.lastname: Young
mesh_terms: D000818:Animals; D031041:Annona / Q000737:chemistry*; D000959:Antihypertensive Agents / Q000008:administration & dosage / Q000302:isolation & purification / Q000494:pharmacology*; D001013:Aorta, Thoracic / Q000187:drug effects / Q000378:metabolism; D001794:Blood Pressure / Q000187:drug effects*; D002118:Calcium / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004730:Endothelium, Vascular / Q000378:metabolism; D006339:Heart Rate / Q000187:drug effects*; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects; D018515:Plant Leaves; D051381:Rats; D017207:Rats, Sprague-Dawley
chemical_list: D000959:Antihypertensive Agents; D002118:Calcium