We tested the hypothesis that severe insulin-induced hypoglycemia would depress cerebrovascular reactivity to CO2 via a mechanism that could be prevented by administration of the N-methyl-D-aspartate (NMDA) receptor antagonist MK-801 in infant piglets. Cerebral blood flow (CBF) was measured (microspheres) in 2- to 3-wk-old pentobarbital-anesthetized piglets during hypocapnia, normocapnia, and hypercapnia. Repeat CBF measurements were made either 1 (n = 5) or 2 h (n = 6) after insulin (200 U/kg iv) to elicit the time course of altered reactivity to CO2. Repeat CBF measurements were made in a third group (n = 5) 2 h after treatment with insulin and MK-801 (1.5 mg/kg iv bolus, 0.15 mg.kg-1.h-1 iv infusion) to determine whether any alteration in reactivity to CO2 was due to a mechanism involving the NMDA receptor. Cerebrovascular resistance and cerebral O2 consumption (CMRO2) were calculated with each measurement of CBF. Cerebrovascular response to CO2 (change in cerebrovascular resistance/change in arterial CO2 tension) was ablated in the group of piglets exposed to 1 or 2 h of hypoglycemia (preinsulin 1-h group, 0.038 +/- 0.007; preinsulin 2-h group, 0.023 +/- 0.004 mmHg.ml-1.min.100 g.mmHg CO2(-1)). Treatment with MK-801 did not alter normoglycemic CO2 reactivity (preinsulin, 0.032 +/- 0.005 mmHg.ml-1.min.100 g.mmHg CO2(-1)) and did not prevent ablation of cerebrovascular CO2 reactivity during hypoglycemia. CMRO2 was not affected by hypoglycemia in any group.(ABSTRACT TRUNCATED AT 250 WORDS)
Effect of Cardiotonic Pills on Erythrocyte Deformability and Cerebrovascular CO2 Reactivity in Normal Subjects
