title: Contractile effect of Sclerocarya birrea (A Rich) Hochst (Anacardiaceae) (Marula) leaf aqueous extract on rat and rabbit isolated vascular smooth muscles.
abstract: BACKGROUND
  Sclerocarya birrea (Anacardiaceae) is traditionally used for treating hypertension. The pharmacological effects of S birrea leaf aqueous extract (SBE) on rabbit and rat vascular smooth muscles were investigated in this study.
  
  
  METHODS
  Fresh S birrea leaves (1 kg) were air dried at 26 ± 1°C, milled, macerated in 2.5 l of distilled water for 48 hours, filtered, and the filtrate was concentrated in a rotary evaporator. Rat isolated portal vein preparations, as well as rabbit isolated endothelium-denuded and endothelium-intact descending thoracic aortic ring preparations were mounted in 30-ml Ugo Basile organ baths under physiological conditions, and challenged with SBE (50-400 mg/ml). The contractile effects of SBE and/or other reference drugs on the isolated vascular smooth muscle preparations were recorded by means of Ugo Basile's force-displacement transducers and Gemini recorders.
  
  
  RESULTS
  SBE (50-400 mg/ml) caused a significant, concentration-dependent upward shift in baseline tone in the aortic ring preparations (p < 0.01-0.001). Indomethacin (20 µM) markedly attenuated the contractile effects of SBE in both the endothelium-intact and -denuded aortic rings, while N(G)-nitro-(L)-arginine methyl ester (L-NAME, 100 µM) significantly (p < 0.05) increased the contractile tension of the endothelium-intact aortic rings. Verapamil (1-3 µg/ml) partially inhibited the contractile effects of SBE. SBE also elicited significant (p < 0.05-0.01) increases in the amplitude of the myogenic contractions of the portal veins. These contractions were abolished by verapamil (1-3 µg/ml) in a concentration-dependent manner, while prazosin (1-3 µg/ml) did not affect the SBE-induced contractions.
  
  
  CONCLUSIONS
  SBE possessed spasmogenic effects on vascular smooth muscle preparations in vitro. It may induce and/or  exacerbate hypertension, contrary to the folkloric, ethnomedical use of S birrea.
authors.affiliation: Department of Pharmacology, School of Pharmacy and Pharmacology, Faculty of Health Sciences, University of KwaZulu-Natal, Durban, South Africa.
authors.forename: T
authors.initials: T
authors.lastname: Mawoza
authors.forename: J A
authors.initials: JA
authors.lastname: Ojewole
authors.forename: P M
authors.initials: PM
authors.lastname: Owira
mesh_terms: D027926:Anacardiaceae; D000818:Animals; D004730:Endothelium, Vascular / Q000187:drug effects; D066298:In Vitro Techniques; D009119:Muscle Contraction / Q000187:drug effects; D009131:Muscle, Smooth, Vascular; D019331:NG-Nitroarginine Methyl Ester; D011817:Rabbits; D051381:Rats; D017208:Rats, Wistar
chemical_list: D019331:NG-Nitroarginine Methyl Ester