Plant material collection: Ripe banana fruits of Musa sapientum (‘sagor’ cultivar) were collected from two district towns within Dhaka division, namely Munshiganj and Narsingdi.
Preparation of methanolic extract of fruit skins For preparation of methanol extract of fruit skins, skins were taken off ripe fruits, thoroughly sliced, dried in the shade, and pulverized into a fine powder. Powder obtained from the fruit skins of two districts were kept and extracted separately. 50g of the powder of each district fruit skins was extracted with 250 ml methanol over 48 hours. Methanol was evaporated at 50 oC and the extract was dissolved in Tween 20 prior to administration to mice by gavaging. Henceforth extract of the fruit skins of fruits obtained from Munshiganj district will be referred to as (MEMSM), and extract of the fruit skins of fruits obtained from Narsingdi district will be referred to as (MEMSN). All extracts were maintained at -20oC prior to use.
Chemicals and Drugs Glibenclamide and glucose were obtained from Square Pharmaceuticals Ltd., Bangladesh. All other chemicals were of analytical grade. Glucometer and strips were purchased from Lazz Pharma, Bangladesh.
Animals Swiss albino mice, which weighed between 14-17g were used in the present study. The animals were obtained from International Centre for Diarrhoeal Disease Research, Bangladesh (ICDDR,B). The animals were acclimatized for three days prior to actual experiments. During this time, the animals were fed with mice chow (supplied by ICDDR,B) and water ad libitum. The study was conducted following approval by the Institutional Animal Ethical Committee of University of Development Alternative, Dhaka, Bangladesh.
Oral glucose tolerance tests for evaluation of antihyperglycemic activity: Oral glucose tolerance tests (OGTT) were carried out as per the procedure previously described by Joy and Kuttan with minor modifications. Briefly, fasted mice were grouped into ten groups of five mice each. The various groups received different treatments like Group 1 received vehicle (1% Tween 20 in water, 10 ml/kg body weight) and served as control, Group 2 received standard drug (glibenclamide, 10 mg/kg body weight). Groups 3-6 received, respectively, (MEMSM) at doses of 50, 100, 200 and 400 mg per kg body weight. Groups 7-10 received, respectively, (MEMSN) at doses of 50, 100, 200 and 400 mg per kg body weight. All substances were orally administered by gavaging. The amount of Tween 20 administered was same in both control and experimental mice. Following a period of one hour as described earlier, all mice were orally administered 2g glucose per kg of body weight. Blood samples were collected 120 minutes after the glucose administration through puncturing heart following previously published procedures [25] . Blood glucose levels were measured with a glucometer. The percent lowering of blood glucose levels were calculated according to the formula described below
Percent lowering of blood glucose level = (1 – We/Wc) X 100
Where We and Wc represents the blood glucose concentration in glibenclamide or (MEMSM) or (MEMSN) administered mice (Groups 2-10), and control mice (Group 1), respectively. Gavaging was done carefully such that injuries do not happen, and no mice fatalities occurred during gavaging. Mice were handled carefully throughout the experiment so that they did not get subjected to any unnecessary pain.
Statistical analysis Experimental values are expressed as mean ± SEM. Independent Sample t-test was carried out for statistical comparison. Statistical significance was considered to be indicated by a p value < 0.05 in all cases.