Hypoglycemic effects of steroidal sapogenins isolated from Jamaican bitter yam, Dioscorea polygonoides.

In this study, three steroidal sapogenins (Delta3 diosgenin, diosgenin, and pennogenin) and the phytosterols, stigmasterol and beta-sitosterol were isolated from Jamaican bitter yam, Dioscorea polygonoides. Their effects on fasting blood glucose and intestinal amylase and ATPases in streptozotocin-induced diabetic rats were studied. The diabetic rats (fed supplemented and unsupplemented diets) lost weight significantly compared to the normal group. There was a significant increase in the activity of alpha-amylase in the proximal region of the small intestinal mucosa of diabetic rats fed sapogenin extract or commercial diosgenin. However, this did not result in increased fasting blood glucose. Instead, supplementation of the diet with bitter yam sapogenin extract significantly decreased fasting blood glucose compared to the diabetic group. Supplementation of the diet with bitter yam sapogenin extract or commercial diosgenin significantly reduced Na+-K+-ATPase activity in all three regions compared to the diabetic control group. Commercial diosgenin supplementation resulted in a significant increase in Ca2+ ATPase activity in proximal region compared to the diabetic control and bitter yam sapogenin extract groups. The effect of bitter yam sapogenin extract or commercial diosgenin on intestinal Na+-K+-ATPase activity could account for their hypoglycemic properties. However, there was adverse effect on the body weight.