PLASMA-GLUCOSE, INSULIN AND CARDIOVASCULAR-RESPONSES AFTER INTRAVENOUS INTRACEREBROVENTRICULAR INJECTIONS OF INSULIN, 2-DEOXYGLUCOSE AND GLUCOSE IN RATS

To determine the possibility that insulin and/or glucose may directly or indirectly modulate cardiovascular tone, we measured plasma glucose , arterial pressure and heart rate after the injection of insulin, 2-o xyglucose (2-DG) and glucose into the femoral vein or into the lateral ventricles of Wistar rats. The systemic administration of insulin sig nificantly decreased plasma glucose, while its intracerebroventricular (ICV) infusion had little effect on plasma glucose, although it resul ted in a significant increase in plasma insulin. Both the peripheral a nd the ICV administration of insulin significantly decreased mean arte rial pressure (MAP) and ICV insulin decreased heart rate. Injections o f 2-deoxyglucose were used to help differentiate the effects of insuli n from those of insulin-induced glucopenia. When infused systemically, 2-DG increased plasma glucose while ICV 2-DG had no significant effec t on plasma glucose levels. When 2-DG was administered systemically, M AP and heart rate were increased slightly; however, they were signific antly decreased when 2-DG was administered centrally. Both ICV and sys temic administration of glucose increased plasma insulin even though I CV glucose did not significantly change the plasma glucose level. Both systemic and ICV administration of glucose significantly decreased MA P and heart rate. These results suggest that increasing the insulin an d/or glucose concentration of the CNS environment may have a direct in fluence on autonomic outflow resulting in decreased MAP and heart rate . Central glucopenia induced by 2-DG suppressed sympathetic or increas ed parasympathetic outflow, while systemic glucopenia stimulated cardi ovascular tone. Both systemic and central glucose administration suppr essed the cardiovascular tone to a lesser extent than did administrati on of insulin. We conclude that CNS glucopenia and/or insulin can modi fy the autonomic control of cardiovascular function in normal rats.