Hypoglycaemic and anorexigenic activities of an (alpha)-amylase inhibitor from white kidney beans (Phaseolus vulgaris) in Wistar rats

An inhibitor of (alpha)-amylase was isolated and purified from an extract of white kidney beans (Phaseolus vulgaris). The acute oral administration of the inhibitor (50 mg/kg body weight) to adult Wistar rats together with a starch load (2 g/kg body weight suspended in NaCl (9 g/l)) reduced the increase in glycaemia over the basal value (NaCl, 222 (SEM 49); inhibitor, 145 (SEM 16) mmol/l*180 min; P<0·05) without modifying the insulin response. On administering the inhibitor orally (50 mg/kg body weight dissolved in NaCl (9 g/l)) for 21 d to rats fed on a standard diet, a decline was observed in the glycaemia values on day 0 (NaCl, 5·53 (SEM 0·12); inhibitor, 5·25 (SEM 0·16) mmol/l) relative to those obtained on days 10 (NaCl, 5·00 (SEM 0·14); inhibitor, 4·60 (SEM 0·08) mmol/l; P<0·05) and 21 (NaCl, 5·22 (SEM 0·22); inhibitor, 4·50 (SEM 0·12) mmol/l; P<0·01) of treatment, without modifying the plasma concentration of insulin. There was found to be a significant anorexigenic action of the inhibitor; there was reduced food intake (NaCl, 23·07 (SEM 0·31); inhibitor, 19·50 (SEM 0·49) g/d; P<0·01), a reduced weight gain (NaCl, 52 (SEM 3); inhibitor, -1·33 (SEM 8·9) g/21 d; P<0·01), as well as changes in the activity of some intestinal enzymes such as maltase (NaCl, 87 (SEM 7); inhibitor, 127 (SEM 11) U/g proteins; P<0·05). The present study has shown, for the first time, that the prolonged administration of an (alpha)-amylase inhibitor reduces blood glucose levels and body-weight gain in Wistar rats.