Regional Cerebral and Neural Lobe Blood Flow during Insulin-Induced Hypoglycemia in Unanesthetized Rats

The effects of hypoglycemia on regional cerebral blood flow (rCBF) were studied in awake restrained rats. The rats were divided into three groups consisting of a normoglycemic control group that received only saline, a hypoglycemic group A, which was given insulin 30 min before flow was measured, and a hypoglycemic group B, which was given insulin 90 and 30 min before flow was measured. Regional CBF was measured using 14C-iodoantipyrine. Mean plasma glucose was 8.76 mumol/ml in the control group, 2.63 mumol/ml in hypoglycemic group A, and 1.51 mumol/ml in hypoglycemic group B. Plasma epinephrine and norepinephrine concentrations increased to approximately 375% and 160%, respectively, of control values in hypoglycemic groups A and B. In the hypoglycemic group A, rCBF significantly increased in three brain regions. In the hypoglycemic group B, rCBF increased significantly in all brain regions measured, with the exception of the neural lobe, in which it decreased. The increase in rCBF ranged from 38% in the hypothalamus to 138% in the thalamus. Neural lobe blood flow significantly decreased by 31%. The neural lobe was the only brain region studied that is not protected by a blood-brain barrier. It may be sensitive to changes in the concentration of vasoactive agents in blood, such as epinephrine and norepinephrine.