Makonnen, Eyasu (Professor)Debella, Asfaw (PhD)Bekele, Addisu2018-06-202023-11-292018-06-202023-11-292016-02http://etd.aau.edu.et/handle/123456789/1956Thymus (Labiatae) is one of the herbs used in the traditional medicine practice in Ethiopia. The claimed actions of thymus are carminative, antimicrobial, anti-spasmodic, relaxing expectorant, astringent, anthelmentic and anti-oxidative. But some people claim and have concern, that thymus causes problems to liver in herbivorous animals that graze on it and human beings who ingest it for different purposes. The aim of the present study was to evaluate the claimed spasmolytic effect and safety of Thymus serrulatus on liver of rats. Experimental study was done in laboratory animals. Charcoal meal test was used to evaluate its spasmolytic effect on mice. Acute toxicity was evaluated by determining LD50 of the plant extracts on mice. Subchronic toxicity was done on rats. Rats were divided into eight groups of five animals each. Four groups were female and the other four were male. Three different doses, 0.2 gm/kg, 1 gm/kg and 2 gm/kg of the aqueous extract were given to the six treatment groups via oral gavage for 90 days. During the study period the animals were observed for any sign of liver toxicity and their body weight was measured weekly. At the end of the study period clinical chemistry parameters, gross morphology and histopathology of the liver were evaluated. The results showed the presence of spasmolytic effect, which is statistically significant difference (P<0.05) for both plant extracts when compared to the negative controls. The 200 mg/kg and 400 mg/kg doses of the methanolic extract have shown more effect than the positive control. No statistically significant difference was observed between the different doses of the aqueous extract and 100 mg/kg dose of the methanolic extract when compared with atropine 10 mg/kg, p.o., which is used as positive control (P>0.05). The oral LD50 for the extract was seen to be higher than 5 gm/kg for both aqueous and methanolic extracts, which is indicative of the plants safety in case of acute high dose exposure. Cage side observation in subchronic toxicity study revealed no sign of liver toxicity. No statistically significant difference (P>0.05) was seen in the clinical chemistry results between the different groups. However, the histologic evaluation revealed cholestatic change of the liver in most of the animals in the treatment group. This may be explained by the presence of phytosterol compounds, in the extract given, which are known to cause cholestasis. Cholestasis was not accompanied by necrosis/degeneration, which could be due to the anti-oxidant and hence protective effect of the active ingredient thymol. In conclusion T. serrulatus has spasmolytic activity and is safe for oral use. Key words: T.serrulatus, toxicity, laboratory animals, extracts.enT.serrulatus; Toxicity; Laboratory animals, extractsThesis