Changes of Pial Vessel Diameter and CO₂ Reactivity during Insulin-induced Hypoglycemia and in the Recovery Period following Glucose Administration

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The present study examined the changes of cerebrovascular CO₂ reactivity during insulin-induced hypoglycemia and in the recovery period following glucose administration in cats. The diameters of pial vessels were continuously measured using the vidicon camera system. Hypoglycemia was induced by intraperitoneal injection of Actrapid^R insulin (100IU/kg). Cerebrovascular CO₂ reactivity was estimated by the changes of pial vessel diameters during 3 min inhalation of 5% CO₂ in air at each stage of glucose level. CO₂ reactivity was impaired in the hypoglycemic stage and this impairment was further enhanced in the early recovery stage. In the late recovery stage, CO₂ reactivity was restored particularly in the small arteries which were less innervated by autonomic nerves. These results suggest that the sympathetic activity plays an important role in the impairment of cerebrovascular CO₂ reactivity during hypoglycemia.