Introduction

Diabetes is the most common disorder, it is a disorder characterised by hyperglycemia or elevated blood glucose (Cidlowski and Keith, 2004).  Diabetes mellitus is a chronic disorder of carbohydrate metabolism thereby affecting protein and fat metabolism (Askar et al, 2003).  There is a defective or deficient insulin secretory response which translates into unpaired carbohydrate (glucose) (Cotran et al, 1999).

Heredity usually plays a major role in determining in whom diabetes will develop and in whom it will not.  Sometimes it does this by increasing the susceptibility of the beta cells to destruction by viruses or by favouring the development of autoimmune antibodies against the beta cells, thus leading to their destruction (Guyton and Hall, 1996).

The pharmacological management of diabetes mellitus has changed dramatically in the past few years with the introduction of many new medications, including a-glucosidase inhibitors, a biguanide, the thizolidinediones, insulin analogs, maglitinides and D-phanylalanine derivatives.  These new agents have dramatically increased the number of options available to providers and patients (Unwin et al, 1999).  Man has been using herbs or plant products as medicine for developing immunity or resistance against cold, joint pains, fever, etc.  However, only very few drugs of plant origin could reach clinical use.  For this reason, a special effort is required for the development of herbal drugs having therapeutic utility (Gupta, 1994).

Musa paradisaca belongs to the plant kingdom Magnoliophyta division, Lipsida class, Zungiberates order, Musaceae family and musa genus (FAO, 2003).  The hypoglycemic activity of methanol exteract of Musa paradisaca green fruits in normal and diabetic mice have been reported which led to the suggestion of folkloric use in the management and control of adult onset (Ojewole and Adewumi, 2003).  This study therefore intends to examine the hypoglycemic effect of aqueous extract of unripe plantain in alloxan-induced diabetic rats.

Materials and Methods

Subject Selection

Adult healthy albino rats of both sexes weighing between 100 – 140g were obtained from the Animal Breeding Unit of the Department of Biochemistry, University of Ilorin, Kwara State, Nigeria.  These rats were kept in well ventilated cages and were allowed free access to water and animal feeds.

Grouping

The rats were divided into four groups of four animals each.  The animals in groups one and two were normal and healthy (non-diabetic) while the animals in groups three and four were made diabetic by the administration of alloxan monohydrate.  Group one served as the control and they received distilled water only.  The animals in group two received aqueous extract of Musa paradisiaca (5% ^w/_v).  Animals in group three were kept as diabetic control (untreated) and were administered distilled water only.  Rats in group four were treated with aqueous extract of Musa paradisiaca equivalent to 100mg/kg body weight orally.  Blood glucose of the animals were routinely determined using one touch glucometer.

Oral glucose tolerance test

The animals were given aqueous extract of Musa paradisiaca (100mg/kg body weight) orally after overnight fasting (18hours).  Two hours later glucose solution (5% ^w/_v) was administered orally at a dose of 100mg/kg body weight also.  Blood samples were collected before the administration of glucose and glucose values were determined at 30, 60, 90 and 120mins later.  The blood samples were drawn from the tips of the tails of the rats by cutting the tips.

Statistical analysis

All results are presented as mean ± 8D.  Data were analysed by the student T-test.  Results were considered statistically significant to P < 0.05.

Result and Discussion

The mean blood glucose levels of normal rat at various time intervals after oral administration of aqueous extract of Musa paradisiaca (100mg/kg body weight) are shown in Table 1.  These levels were compared with the values in control rats administered distilled water alone.  Aqueous extract of Musa paradisiaca lowered the blood glucose significantly 6 hours after administration (50.25 ± 7.10mg/dl to 41.00 ± 3.40mg/dl) 24 hours after administration (P < 0.05).  However no differences in blood glucose level (P > 0.05) were observed during the period of 2 hours to 4 hours after administration when compared with control.  This implies that hypoglycemic effect of the extract was not felt until 6 hours after administration.

Table 1: Effect of 5% Aqueous Extract of Musa paradisiaca (100mg/kg) on Blood Glucose (mg/dl) in Normal Rats.

Each value represents the mean ± SD from 4 rats

Significantly different from the control at P < 0.05

Animals treated with aqueous extracts of Musa paradisiaca (5% ^w/_v) showed significant decrease (P < 0.05) in blood glucose level from 4 hours 532.50 ± 43.70mg/dl to 499.00 ± 45.72mg/dl (8 hours after administration).  The blood glucose level later increase at 10 hours (517.00 ± 67.76mg/dl) and decrease consistently from 12 hours to 24 hours after administration (460.50 ± 40.40mg/dl).

It is possible that the hypoglycemic principle in the aqueous extract exert a direct effect on the diabetic rats, probably by a mechanism similar to insulin.  The treatment with 5% aqueous extracts resulted in weight gain as revealed in the growth pattern curve (Fig. 1).

Figure 1: Growth Response of Diabetic Rats Treated with Aqueous Extract of Musa paradisiaca.   Click here to View figure

The glucose tolerance of rats after oral glucose loading is shown in Table 2.  Normal animals treated with aqueous extracts of Musa paradisiaca showed significant decrease (P < 0.05) in blood glucose level during the period of 30 to 120mins after glucose loading when compared to the basal value (0 min).  This implies that an effective glucose tolerance and utilisation shown in normal treated rat is due to the hypoglycemic activity of the extract which either stimulates glycolysis in tissues with increase glucose removal from blood and also reduced hepatic gluconeogenesis.

Table 2: Effect of 5% Aqueous Extract of Musa paradisiaca (100mg/kg) on Blood Glucose (mg/dl) in Alloxan-induced Diabetic Rats.

Each value represents the mean ± SD from 4 rats

In untreated rats (hyperglycaemic) an improper glucose tolerance and utilisation was observed (Table 3).  There was increase in blood glucose level at 120mins.  According to Guyton and Hall (1999), diabetic patients upon ingestion of glucose exhibit a much greater than normal rise in blood glucose level, it comes down to normal level much slower because insulin is either not produced or when produced cells of the body does not respond to it and also impair the secretion of insulin.

Table 3: Glucose Values (mg/dl) During Oral Glucose Tolerance Test in Normal and Alloxan-induced Diabetic Rats.

Each value represents the mean ± SD from 4 rats

Significantly different from the control at P < 0.05

In conclusion, the present study clearly shows that the aqueous extract of Musa paradisiaca produces consistent hypoglycemic effect in normal rats as well as in hyperglycemic rats over a short period of time (24hrs).  Longer periods of treatment may exert a more pronounced therapeutic effect.

References

1. Askar, M. A; Banguer, N. Z; Muorty, K; Taha, A and Yadav, U. C. (2003) Changes in Key enzymes of metabolic pathways of diabetic rat tissues with oral hypoglycemic compounds.  International Diabetes Federation Congress p2355.
2. Cidlowski, A. J. and Keith, L. H. (2004) Diabetes symptoms diagnosis and insulin treatment.  Journal of Clinical Endocrinology and Metabolism 53: 1 – 11.
3. Cotran, R. S; Tucker, C. and Viney, K. (1999) The pancreas Pathologic Basis of Disease 6^th Edition 902 – 929.
4. FAO (2003) Banana Commodity notes find result of the 2003 season.
5. Gupta, S. S. (1994) Prospects and perspectives of natural plants products in medicine.  J. Pharmacol 26: 1 – 12.
6. Guyton, A. C. and Hall, E. J. (1999) Insulin, Glycogen and Diabetes Mellitus In: Textbook of Medical Physiology 9^th Edition 971 – 983.
7. Ojewole, J. A. and Adewumi C. O. (2003) Hypoglycemic effect of Methanolic extract of Musaparadisiaca (Musaceae) green fruits in normal and diabetic mice.  Method and findings in clinical pharmacology 25(6) 453 – 456.
8. Unwin, N.; Mugus, S.; Aspary, T. (1999) Tackling the emerging pandemic of non-communicable diseases in sub-Saharan Africa: the essential NCO health intervention project.  Public Health 29 – 107.