MECHANISTIC STUDIES OF MYORELAXANT EFFECTS OF ETHANOLIC LEAF EXTRACT OF ERIOBOTYRA JAPONICA ON ISOLATED RABBIT ILEUM
Objectives: The leaves of Eriobotrya japonica are ethnopharmacologically used to treat iarrhea, asthma and hypertension in Zimbabwe. This study was aimed at determining the effect of Eriobotrya japonica on ileum smooth muscles. Materials and methods: E. japonica plant extracts were prepared and tested on isolated rabbit ileum tissue. Plant effects were compared with histamine, Ach or KCl induced contractions to evaluate its gut modulator effects. Adrenergic activity was also tested using propranolol.
Results & Discussion: E. japonica (66-1000μg/ml) ethanolic leaf extract exhibited a dose dependant relaxant effect on spontaneously contracting isolated rabbit ileum. It also dose dependently inhibited rabbit ileum strips precontracted with histamine (0.001M), Ach (0.001M) and K+ (80 Mm) with EC50 values of 322±1.1μg/ml, 335±1.1μg/ml and 325.9 ± 1.10μg/ml respectively. The extract showed inhibition trends that were similar to the positive controls. Chlopheniramine relaxed the smooth muscle by blocking the contractile effects of Ach, EC50 value 383.3 ± 1.44μg/ml. Acetylcholine induced inhibition was similar to that caused by atropine an anticholinergic compound, EC50 value 729±1.13μg/ml. The extract inhibited potassium induced contractions in a dose dependent manner with an EC50 value of 325.9 ± 1.10μg/ml. Propranolol increased smooth muscle relaxation by 73.7% which was similar to the plant extract which increased relaxation by 77.75%. Conclusions: The results suggest that the ethanolic leaf extract of Eriobotrya japonica has myorelaxant effects and may be acting by potentially inhibiting
acetylcholine, histamine and potassium receptors on the rabbit ileum. The effect on adrenergic agonist propanolol activity was inconclusive and needs further testing.