Abstract: | —In living rats the concentration of insulin in the circulating blood was raised and independently of this the glucose concentration in the blood plasma was varied from hyperglycaemic to hypoglycaemic levels. Hyperglycaemia increased the influx of glucose into the brain and it also, for a limited period, increased the glucose gain by the brain. Insulin, on the other hand, did not affect influx but significantly increased the gain of glucose by the brain. It is suggested that although both hyperglycaemia and insulin can increase glucose gain by the brain they do so in entirely different ways. |