Pharmacological actions of Heteromorpha trifoliata ("dombwe") on rat isolated muscle preparations.

OBJECTIVE: To investigate the effects of Heteromorpha trifoliata on rat uterine and skeletal muscle. DESIGN: Laboratory based study using experimental animals. Investigating the effects of the plant extract and agonists on isolated muscle preparations. SETTING: Department of Physiology, University of Zimbabwe. SUBJECTS: 28 Sprague-Dawley rats. MAIN OUTCOME MEASURES: Amplitude of contraction of uterine smooth muscle and skeletal muscle. RESULTS: Experiments were performed on the isolated rat uterus preparation in which strips of myometrium were placed in tissue baths filled with Kreb's solution. The aqueous extract of the root bark of Heteromorpha trifoliata ("dombwe") contracted the rat uterus. The contractions were not antagonised by atropine but were blocked by both cyproheptadine and verapamil. In addition, "dombwe" induced a contracture of the rat diaphragm muscle in the presence of alcuronium. CONCLUSIONS: The contractile effects on the uterus appear to involve stimulation of 5-HT2 receptors leading to an increase in calcium influx into the smooth muscle cell. Promotion of calcium influx could also explain the effects observed on the skeletal muscle preparation since the contracture induced by "dombwe" occurred in the presence of the nicotinic antagonist, alcuronium. In view of the effects of "dombwe" on other smooth muscle preparations (from previous work) it appears that the pharmacological profile of the crude aqueous extract of the root bark of Heteromorpha trifoliata is complex and suggestive of the presence of more than one active ingredient.