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    • g protein coupled receptors In the present study compared to

    2021-11-23

    In the present study, compared to diabetic control rats, hepatic glucose-6-phosphatase activity was significantly decreased in both SE and METF treated diabetic animals, with the latter producing greater reduction in glucose-6-phosphatase activity. This observation is consistent with the claim of Tahrani et al.[22] and Jung et al.[23] who posited that metformin is an established inhibitor of glucose-6-phosphatase. The ability of SE extract to reverse the STZ-induced upsurge in glucose-6-phosphatase is suggestive of a pro-insulin effect for the extract. The extract may have promoted insulin secretion from the beta g protein coupled receptors of the pancreas, consequently enhancing glucose mobilization into the cells and slowing down the process of glycogenolysis and gluconeogenesis in which glucose-6-phosphatase is a key player. This postulation is in line with a previous report by Massillon et al.[5], who noted that control of blood glucose level in diabetes with insulin usually results in decreased gucose-6-phosphatase gene expression and activity. It also explains the relative improvement in hepatic glycogen level observed in SE and METF treated diabetic rats compared to diabetic control animals in which the activity of the enzyme was significantly elevated. Anti-diabetic effects of SE extract has been noted in another work in our laboratory, and deactivation of glucose-6-phosphatase activity as observed in this study is probably one of the mechanisms by which SE extract elicits its antidiabetic potential. Meanwhile, like SE, a number of other plants have been reported to exhibit hypoglycemic activity primarily through inhibition of glucose-6-phosphatase. Few examples are Cecropia obtusifolia[24], Malmea depressa[25] and Tinospora cordifolia[9]. When compared to SE, the significantly greater effect of METF on glucose-6-Phosphatase activity may be responsible for the higher glycogen contents observed in the liver of diabetic rats treated with the reference drug. Glucokinase is another glucose metabolism enzyme, it is found mainly in the liver and pancreas. Pancreatic glucokinase play a very important role (as a glucose sensor) in ensuring appropriate secretion and release of insulin vis-à-vis plasma glucose concentration. The enzyme like its liver counterpart is activated by high plasma glucose concentration (>7.5 mM) and becomes deactivated when the glucose level drops to normal (<5.5 mM) [8]. According to Alberti et al.[26] within normal physiological glucose concentrations hepatic glucokinase is usually in its inactive form, bound to regulatory protein. However, secondary to upsurge in plasma glucose concentration, the enzyme is activated and release from its bound protein molecule into the cytoplasm where it facilitates the breakdown of glucose through glycolysis as one of the means of maintaining glycaemic balance [27]. In this study, hepatic glucokinase activity was observed to decrease significantly in diabetic control animals compared to normal control animals, suggesting a compromise in enzymatic regulatory mechanism. The suppressed enzyme activity is likely as a result of STZ induced conformational alteration in the enzyme molecule. Zhang et al.[16] had previously associated the decreased activity of glucokinse observed in similar studies to STZ induced free radical damage. This observation is very important because of the role of the enzyme in hepatic glucose homeostasis. It catalyzes the rate limiting step of glycolysis by phosphorylating glucose to glucose -6-phosphate. Down regulation of glucokinase activity will therefore contributes to the onset and progression of diabetes mellitus. This assertion is further validated by the report of Zhang et al., [16] which associated gene mutation in glucokinase with a form of diabetes known as maturity onset diabetes of the young. Compounds that elicit stimulatory effect on the activity of glucokinase have been reported to enhance the regulatory function of the enzyme in drug-induced diabetes in animal model [27], [28].