Inhibitory effects of the volatile oils of Callistemon citrinus (Curtis) Skeels and Eucalyptus citriodora Hook (Myrtaceae) on the acetylcholine induced contraction of isolated rat ileum

Using steam distillation method, the volatile oils of Eucalyptus citriodora and Callistemon citrinus were obtained and their chromatographic profiles examined in hexane: ethylacetate (4:1; 7:3) and hexane-chloroform (7:3). The effects of the volatile oils on acetylcholine (Ach) induced contraction of the rat isolated ileum were investigated based on the ethnomedicinal use of the volatile oil of E. citriodora in treating diarrhoea. Relative to the weight of the fresh leaves (200g in each case), E. citriodora produced 0.75% of the volatile oil while the C. citrinus yielded 0.5%. Combination of hexane-ethylacetate (4:1) gave the best resolution of the constituents as E. citriodora produced six major spots while Callistemon citrinus produced three. The concentration-dependent contractions of the ileum produced by the increasing concentration of the Ach were observed to be remarkably attenuated in the presence of the volatile oils at 5 and 10 mg/ml. At 5mg/ ml, the volatile oils of E. citriodora and C. citrinus independently reduced the Ach maximum contraction to 74.11 ± 12.4 and 19.05 ± 5.17% respectively. At 10mg/ml, the volatile oils further significantly (P 0.05) inhibited the contraction induced by the Ach. The results obtained validated the ethnomedicinal use of the volatile oils particularly that of E. citriodora in reducing ilea contractions occasioned by diarrhoea. However, C. citrinus volatile oil seems to be more effective.