Temporary suppression of the hyperglycemic response to 2-deoxy-D-glucose by blinding.

Studies were made on whether there is a time-dependency in the hyperglycemic response to intracranial injection of 2-deoxy-D-glucose (2DG) in blind rats. 2DG was given to blind rats in their subjective light and dark periods to see if the response free-runs like their circadian locomotor and feeding rhythms. The following results were obtained: (1) In control period and week 3 after blinding, 2DG caused greater hyperglycemia in the subjective light period than in the subjective dark period; (2) In weeks 4 and 6, however, 2DG caused only slight hyperglycemia, while it caused considerable hyperinsulinemia in both the subjective light and dark periods with no time-dependency. (3) In week 8, the hyperglycemic response to 2DG was completely restored while the hyperinsulinemic response was lost. These findings indicate that the subjective time-dependency in the hyperglycemic response to intracranial injection of 2DG exists until week 3 and after week 8 after blinding, however, in week 4 and 6 after blinding the subjective time-dependency appeared to disappear and the hyperglycemic response is largely suppressed in association with hyperinsulinemia. Together with a previous finding that bilateral lesions of the SCN completely abolished the response to 2DG and the fact that blind rats showed circadian rhythms of feeding and locomotive activity even in weeks 4 and 6 after blinding, these findings present the possibility that the site responding to 2DG is in the vicinity of the SCN, but is in different neuronal cells from those of the circadian oscillator. However, it is also possible that the blinding elicits the suppression of hyperglycemia due to 2DG through disturbing neural pathway outside the SCN which control blood glucose concentration.