Hypoglycemic effect of guava (Psidium guajava Linn.) leaf extracts in streptozotocin-nicotinamide induced type 2 diabetic rats
Date Issued
2007
Date
2007
Author(s)
Wu, Ning-Jung
DOI
zh-TW
Abstract
Diabetes mellitus (DM) is one of the major diseases that human being eagerly wants to overcome. In 2006, DM was the fourth of top ten causes of death in Taiwan and more than 95% are type 2 DM. Guava (Psidium guajava Linn.) is one of the most important economic fruit in Taiwan. Leaves and fruit of guava are believed to have hypoglycemic effects which have been popularly employed in traditional DM treatment in Taiwan. However, there is insufficient scientific evidence for guava to cure DM, especially type 2 DM. In the present study, we injected low-dose streptozotocin (STZ) plus nicotinamide (NA) into Sprague-Dawley (SD) rats to induce Type 2 diabetes and to evaluate the antihyperglycemic effect and the carbohydrate metabolism of water and ethanol extracts from guava leaves. The study contains two parts, the acute and the long term experiments. In the acute experiment, the water or ethanol extracts of guava leaves were prepared and in the oral glucose tolerance test (OGTT) was performed to evaluate the hypoglycemic effects. In the long term experiment, we investigated the effect of aqueous or ethanol extracts from guava leaves in STZ–NA induced diabetic rats daily administered for 6 weeks.
Results of the acute experiment showed that plasma glucose levels of the diabetic rats administered with 200 or 400 mg/kg BW of aqueous or ethanol guava leaf extracts were lower than the diabetic control group (p<0.05). This indicated that aqueous or ethanol extracts from guava leaves could effectively delay the rise of plasma glucose after feeding in diabetic rats. Diabetic rats administered with 400 mg/kg BW of aqueous or ethanol guava leaf extracts significantly reduced plasma glucose than 200 mg/kg BW. Therefore, aqueous or ethanol extracts from guava leaves with dosage of 400 mg/kg BW were used to carry out the long term experiments.
The result of the long term experiments, showed that the diabetes groups fed with 400 mg/kg BW of aqueous or ethanol guava leaf extracts presented a significantly reduction of blood sugar level comparing to diabetes and normal groups (both fed with saline) and could delay the elevation of plasma glucose during the OGTT test after the fourth and sixth weeks. The rats were sacrificed at the 6 weeks and the carbohydrate metabolism enzyme activities in liver were measured. The activities of hexokinase, phosphofructokinase, and glucose-6-phosphate dehydrogenas in diabetic rats fed with aqueous guava leaf extracts were higher than those of diabetic control rats (p<0.05), while the activity of fructose-1, 6-bisphosphatase and glucose-6-phosphatase was markedly lower than diabetic control rats (p<0.05). In addition, the activities of hexokinase and glucose-6-phosphate dehydrogenase in diabetic rats fed with ethanol guava leaf extracts were higher than diabetic control rats, while the activities of phosphofructokinase, fructose-1, 6-bisphosphatase, and glucose-6-phosphatase were no different with each group. The blood glucose reduction ability of extracts from guava leaves in diabetic rats may be related with the activity of hepatic carbohydrate metabolic enzymes. In additional, the abilities of glucose uptake and glycogen synthesis are significantly promoted in hepatocytes of diabetic rats treated with aqueous or ethanol extracts from guava leaves. These results indicate that extracts of guava leaves may regulate the plasma glucose in STZ–NA induced type 2 diabetic rats.
Subjects
番石榴
糖
尿
病
降
血糖
作用
口服葡萄糖
耐受性試驗
碳水化合物代謝
Psidium guajava Linn.
diabetes
antihyperglycemic effect
OGTT
carbohydrate metabolism
SDGs
Type
thesis
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