Enhanced [3H] glutamate binding in the cerebellum of insulin-induced hypoglycaemic and streptozotocin-induced diabetic rats.
OBJECTIVE
Energy deprivation causes neuronal death affecting the cognitive and memory ability of an individual. The kinetic parameters of glutamate dehydrogenase (GDH), the enzyme involved in the production of glutamate, was studied in the cerebellum and liver and the binding parameters of glutamate receptors in the cerebellum of insulin-induced hypoglycaemic and streptozotocin-induced diabetic rats were studied to reveal the role of glutamate excitotoxicity.


METHODS
A single intrafemoral dose of streptozotocin was administered to induce diabetes. Hypoglycaemia was induced by appropriate doses of insulin subcutaneously in control and diabetic rats. The kinetic parameters V (max) and K (m) of GDH were studied spectrophotometrically at different substrate concentrations of alpha-ketoglutarate. Glutamate receptor binding assay was done with different concentrations of [3H] Glutamate.


RESULTS
The GDH enzyme assay showed a significant increase (P < 0.001) in the V (max) of the enzyme in the cerebellum of hypoglycaemic and diabetic rat groups when compared to control. The V (max) of hypoglycaemic groups was significantly increased (P < 0.001) when compared to diabetic group. In the liver, the V (max) of GDH was significantly increased (P < 0.001) in the diabetic and diabetic hypoglycaemia group when compared to control. The V (max) of GDH increased significantly (P < 0.001) in the diabetic hypoglycaemic rats compared to diabetic group, whereas the control hypoglycaemic rats showed a significant decrease in V (max) (P < 0.001) when compared to diabetic and diabetic hypoglycaemic rats. The K (m) showed no significant change amongst the groups in cerebellum and liver. Scatchard analysis showed a significant increase (P < 0.001) in B (max) in the cerebellum of hypoglycaemic and diabetic rats when compared to control. The B (max) of hypoglycaemic rats significantly increased (P < 0.001) when compared to diabetic group. In hypoglycaemic groups, B (max) of the control hypoglycaemic rats showed a significant increase (P < 0.001) compared to diabetic hypoglycaemic rats. The K (d) of the diabetic group decreased significantly (P < 0.01) when compared to control and control hypoglycaemic rats. There was a significant decrease (P < 0.05) in the K (d) of diabetic hypoglycaemic group when compared to the control hypoglycaemic rats.


CONCLUSIONS
Our studies demonstrated the increased enzyme activity in the hypoglycaemic rats with increased production of extracellular glutamate. The present study also revealed increased binding parameters of glutamate receptors reflecting an increased receptor number with increase in the affinity. This increased number of receptors and the increased glutamate production will lead to glutamate excitotoxicity and neuronal degeneration which has an impact on the cognitive and memory ability. This has immense clinical significance in the management of diabetes and insulin therapy.
Joseph
Anu
A
Department of Biotechnology, Cochin University of Science and Technology, Cochin, Kerala, 682 022, India.
Robinson
Remya
R
Paulose
C S
CS
D000818:Animals; D001665:Binding Sites; D002531:Cerebellum / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D003921:Diabetes Mellitus, Experimental / Q000150:complications / Q000201:enzymology / Q000378:metabolism*; D005969:Glutamate Dehydrogenase / Q000378:metabolism; D018698:Glutamic Acid / Q000378:metabolism*; D007003:Hypoglycemia / Q000201:enzymology / Q000209:etiology / Q000378:metabolism*; D007328:Insulin; D008099:Liver / Q000201:enzymology; D008297:Male; D011485:Protein Binding; D051381:Rats; D017208:Rats, Wistar; D017470:Receptors, Glutamate / Q000378:metabolism; D013311:Streptozocin; D014316:Tritium / Q000493:pharmacokinetics