African Journal of Traditional, Complementary and Alternative Medicines African Ethnomedicines Network ISSN: 0189-6016 Vol. 3, Num. 2, 2006, pp. 21-26

African Journal of Traditional, Complementary and Alternative Medicines Vol. 3, No. 2, 2006, pp. 21-26

Research Paper

ANTIDIABETIC ACTIVITY OF ETHANOLIC LEAF EXTRACT OF CROTON ZAMBESICUS MUELL.(THUNDER PLANT) IN ALLOXAN DIABETIC RATS

*J. E. Okokon,  A. L. Bassey and J. Obot,

Department of Pharmacology & Toxicology, Faculty of Pharmacy, University of Uyo, Uyo, Nigeria E-mail: judeefiom@yahoo.com

Code Number: tc06028 

Antidiabetic activity of ethanolic leaf extract of Croton zambesicus Muell. Arg. was evaluated using alloxan-induced (150mg/kg) hyperglycaemic rats. The activity of the ethanolic leaf extract was compared with that of a reference drug Chlorpropamide. The Blood Glucose Levels were measured using glucometer. The extract produced a significant (P<0.01) reduction in BGL after a single dose of the extract and in prolonged treatment (for 7 days). The antidiabetic activity was comparable to that of the reference drug-chlorpropamide.

Key words: Croton zambesicus,antidiabetic, alloxan

Introduction

Croton zambesicus Muell Arg. (Euphorbiaceace) (syn C. amabilis Muell. Arg. C. gratissimus Buch) is an ornamental tree grown in villages and towns in Nigeria. It is a Guineo-Congolese species widely spread in tropical Africa. The leaf decoction is used in Benin as anti hypertensive and anti-microbial (urinary infections) and to treat fever associated with malaria (Adjanohoun et al.,1989) and in parts of Nigeria as antidiabetic and malarial remedy. Block et al., (2002) reported that ent-trachylobane diterpene, isolated from dichloromethane extract of the leaves has cytotoxic activity on Hela cells. Studies have reported on the antimicrobial properties of the leaf and stem (Abo et al., 1999). The essential oil found in the leaves contain P-cymene, linalool and beta-caryophyllene (Menut et al., 1995). The constituent of the essential oil also found in the flowering tops are pinene, limonene, methol, carvone, thymol, alpha – humulene and ceisnerolidol (Mekkawi, 1985). The ethanolic leaf extract has been reported to possess antiplasmodial activity (Okokon et al., 2005). Although a number of studies have been carried out on this plant, there is no scientific report on the hypoglycaemic activity of this plant grown in Nigeria. We, therefore investigated the above property of the plant  to confirm it’s use traditionally.

Preparation of plant extract

The leaves of C. zambesius Muell. Arg. (Euphorbiaceae) were collected in November 2004 at Uyo area of Akwa Ibom StateNigeria and authenticated by Dr. Margaret Bassey a taxonomist in the department of Botany, University of Uyo, Uyo, Nigeria. Herbarium specimen number of the plant is FPUU 209. The fresh leaves (2kg) of the plant were dried on a laboratory table for 8 days and reduced to power. The powder 100g was macerated in 95% ethanol (300ml) for 72 hours. The liquid extract obtained was concentrated in vacuo at 40°C. The yield was 3.77%. The extract was stored in a refrigerator at 4°C until used.

Animals

Albino wistar rats (139-220g) of either sex were obtained from the University of Uyo animal house. They were maintained on standard animal pellets and water ad libitum. Permission and approval for animal studies were obtained from the College of Health Sciences Animal Ethics Committee, University of Uyo.

Determination of LD₅₀

The LD₅₀ of the extract was estimated using swiss albino mice by intraperitoneal (i.p. route using the method of Lorke (1983).

Alloxan monohydrate (BDH) 150mg/kg body weight was injected intraperitoneally to induce hyperglycemia (Yanardag and Colak, 1998). The experimental animals were fasted for 18h before alloxan injection. After one hour of alloxan administration the animals were fed ad libitum.

The Blood Glucose Level (BGL) was monitored after alloxanisation in blood samples collected by amputation of the tail tip under mild anaesthesia. The blood was dropped on the dextrostix reagent pad. The strip was inserted into microcroprocessor digital blood glucometer and the reading were noted (WHO, 1980). After 72 hours rats having BGL beyond 150mg/dl of blood were selected for the study and divided into five groups of five animals each. The extract 100, 150 and 200 mg/kg were orally administered to respective groups of animals. The reference drug chlorpropamide (100mg/kg) and normal saline were also administered orally to two groups of animals representing reference and control groups respectively. The above treatments were carried out in each group of animals for seven consecutive days. The blood glucose level was monitored after 1, 3, 6 and 12 h of administration of a single dose of the extract (for acute study) and at the end of 1, 2, 3 and 7 days (prolonged treatment).

Data obtained were analysed using student’s t-test to determine the statistical significance of the change in BGL.  P < 0.05 was considered significant.

Results

Acute toxicity

The extract (100-200mg/kg) produced physical signs of toxicity ranging from decreased motor activity, writhing, decreased respiratory rate, body and limb tone to death. The intensities of all these effects were proportional to the dose administered. The LD₅₀ of the extract in mice was 1400 ±148 mg/kg.

Table 1:  Effect of C. zambesicus on blood glucose levels of alloxan diabetic rats after a single dose. 

n = 5,   * P < 0.01 Vs control

Table 2:  Efect of c. zambesicus on blood glucose levels of alloxan diabetic rats after prolonged treatment 

n = 5,   * P < 0.01 Vs control

Administration of ethanolic leaf extract of C. zambesicus (100-200mg/kgg) to alloxan –diabetic rats produced a significant (p<0.01) reduction in BGL of the diabetic rats in a dose dependent fashion after a single dose of the extract and in prolonged treatment (7 days) compared to control group. The hypoglycaemic activity of the extract was sustained throughout the monitoring period. At 12 hours after a single dose of the extract about 59.6+3.04% reduction in the BGL of the alloxanized rats was recorded almost comparable to that of the reference drug (chlorpropamide) (Table 1). The extract (100-200mg/kg) produced a sustained significant (P<0.01) hypoglycaemic effect during prolonged treatment (7days) and this was comparable to that produced by the reference drug (Table 2).

A number of plants have been used traditionally to treat diabetes and some have been proven scientifically and reported to have hypoglycaemic effect. These studies on hypoglycaemic activity of plants have identified compounds like polysaccharides (Tomoda et al, 1985), flavonoids (Schimizu et al,1984), terpenoids and Tannins (Reher et al, 1991) steriods (Ivorra et al, 1989), glycoprotein (Hikino et al, 1989), polypeptides (Khana and Jain, 1981) and alkaloids (Karawya and Wahab,1984) to be responsible for this action. C. zambesicus ethanolic leaf extract have been reported to contain saponins, alkaloids, terpenes, flavonoids and cardiac glycosides among others (Okokon et al,2004).The observed hypoglycaemic effects of this plant could have resulted from the combined activity of these compounds present in the leaf extract. Sulphonylureas cause hypoglycemia by stimulating insulin releases from pancreatic beta cells. The effects of the sulphonylureas are initiated by binding  and blocking  an ATP- dependent potassium channels present in the beta cell membrane  in the pancreatic islet cells(Aguillar-Bryan et al, 1995).Moreso, studies have reported on hypoglycaemic activty of Croton cajucara, a species in the same genus.trans- Dehydrocrotonin, a nor – clerodane diterpene isolated from the plant was found to exert significant hypoglycaemic activity in alloxan induced diabetic rats(Farias et al,1997).Isolation from the leaves of Croton zambeslcus of four diterpinoids compounds have been reported(Block et al,2002;Block et al,2004).Also,labdane,clerodane and trachylobane diterpenes have been identified in the stem bark of Croton zambesicus (Ngadjui et al,2002).This further points to the involvement of the diterpenes present in the leaves in this activity. Sulphonylureas compounds are potent in mild alloxan-induced diabetes and inactive  in  intense alloxan diabetes where nearly all  beta cells have been destroyed (Yallow et al, 1960). The observed reduction in blood glucose  level of hypergylcaemic animals by chlorpropamide in our study  portrays  an insevere  state of diabetes. Moreover, the comparable pattern of hypoglycaemic activity of the extract under study with that of the reference drug, chlorpropamide, demonstrated a possible similarity in their mechanism of action to increase insulin secretion.

This observation confirms the use of this plant in ethnomedical practice for diabetes management. It also warrant further investigation to isolate and identify the hypoglycaemic principles in this plant so as to elucidate it’s mode of action.

The authors are grateful to Mr. Nsikak Malachy of Pharmacology Dept, University  of  Uyo, Uyo for technical assistance.

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