Endocrine Abstracts

Hypoglycaemia and hypoglycaemia unawareness severely limit the optimal management of diabetes mellitus and cause recurrent morbidity and even mortality in intensively controlled patients. Altered hypothalamic glucose sensing has been implicated in the development of defective counter regulatory responses to insulin induced hypoglycaemia and hypoglycaemic unawareness. This change in hypothalamic glucose sensing has been attributed, at least in part, to an increase in glucokinase activity in the ventromedial hypothalamus (VMH) following insulin induced hypoglycaemia. An increase in VMH glucokinase is also noted in fasting rats. This suggests that VMH glucokinase may have an important role in mediating physiological responses that restore normoglycaemia during glucoprivation.

To test this hypothesis we stereotactically injected recombinant adeno-associated virus (rAAV) encoding glucokinase (n=11) or GFP (n=9, controls) into the VMH of adult male Wistar rats. Glucokinase expression in the VMH was confirmed using in situ hybridisation. We tested the role of glucokinase in gradual-onset hypoglycaemia during fasting. Blood glucose was measured, in mmol/l, in the fed state and following a 24 or 48 h fast. There was no significant difference in blood glucose levels, at baseline (GFP: 5.38±0.38 versus glucokinase: 5.56±0.48, P=0.39), 24 h (GFP: 3.88±0.28 versus glucokinase 3.92±0.66, P=0.83) or 48 h (GFP: 3.87±0.62 versus glucokinase: 3.74±0.61, P=0.64).

Altering glucokinase activity in the VMH, using adeno-associated viral gene transfer, offers an attractive and novel method to study the importance of VMH glucose sensing on responses to hypoglycaemia. Our initial results suggest that an increase in VMH glucokinase activity does not affect glucose homeostasis in response to gradual onset hypoglycaemia induced by fasting. Further work is needed to assess the role of VMH glucose sensing in acute glucoprivation, as observed in insulin induced hypoglycaemia.