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Effects of metformin on insulin receptor tyrosine kinase activity in rat adipocytes
Abstract:
The cellular mechanism(s) by which the biguanide, metformin, exerts its antihyperglycaemic effect was investigated. Rat adipocytes were either treated acutely (2 h) or maintained in a biochemically defined medium (20 h) in the presence or absence of metformin (1 X 10(-4) mol/l). Exposure to the drug resulted in a significant enhancement (p less than 0.01) of hexose transport in both the absence (basal) and presence of insulin. Stimulation of transport was not explained by the increase in the basal state alone, since the incremental response to maximally effective concentrations of insulin was significantly enhanced p less than 0.025. Insulin-receptor tyrosine kinase activity was examined under the same experimental conditions. Activity of the kinase was unaltered as evaluated by phosphorylation of an artificial substrate and by phosphorylation of the receptor in situ. Furthermore, in this investigation neither insulin receptor number nor affinity was changed in adipose tissue treated with metformin. These studies indicate that metformin potentiates the effect of insulin on glucose transport at a site(s) beyond insulin receptor binding and phosphorylation.
Insights
Metformin enhances glucose transport in rat adipocytes by acting beyond insulin receptor binding. This biguanide medication boosts sugar uptake, improving its effectiveness in managing high blood sugar levels.
Area of Science:
- Biochemistry
- Cell Biology
- Pharmacology
Background:
- Metformin is a widely used biguanide medication for managing hyperglycemia.
- The precise cellular mechanisms underlying metformin's antihyperglycemic effects require further elucidation.
Purpose of the Study:
- To investigate the cellular mechanisms of metformin's antihyperglycemic action.
- To determine if metformin affects insulin signaling pathways in rat adipocytes.
Main Methods:
- Rat adipocytes were treated with metformin (1 X 10(-4) mol/l) for acute (2 h) or chronic (20 h) periods.
- Hexose transport was measured in the presence and absence of insulin.
- Insulin receptor tyrosine kinase activity was assessed via substrate and in situ receptor phosphorylation.
- Insulin receptor number and affinity were evaluated.
Main Results:
- Metformin significantly enhanced hexose transport in rat adipocytes under basal and insulin-stimulated conditions (p < 0.01).
- The incremental response to insulin was significantly potentiated by metformin (p < 0.025).
- Metformin did not alter insulin receptor tyrosine kinase activity, receptor number, or affinity.
Conclusions:
- Metformin potentiates insulin's effect on glucose transport.
- The mechanism of action is located downstream of insulin receptor binding and phosphorylation.
- Metformin's effects on glucose transport occur at a post-receptor level.