Influence of cholinergic blockade on the cerebral blood flow response to exercise in humans (1183.3)

Abstract

Administration of the muscarinic cholinergic receptor blocker glycopyrrolate reportedly attenuates the exercise‐induced increase in middle cerebral artery mean blood velocity. We sought to determine the cholinergic contribution to blood flow in the internal carotid artery (ICA; duplex Doppler ultrasound) during low (42±9 Watts; mean±SE) and moderate (110±11 Watts) intensity leg cycling in seven young male subjects (21±1 yr). Mean arterial pressure (MAP) and heart rate (HR; ECG) were continuously monitored. Stroke volume (SV) was determined offline using Modelflow and cardiac output calculated (CO=HR×SV). Exercise trials were conducted under control (no drug) conditions and after cholinergic blockade by administration of glycopyrrolate. Cholinergic blockade increased resting CO (6.8±0.4 to 8.7±0.5 L/min; P<0.05) and MAP (79±2 to 89±3 mmHg), while the responses to exercise were similar. ICA blood flow increased similarly from rest during low and moderate intensity exercise under control (271±34, 333±27 and 361±28 mL/min, respectively, P<0.05) and cholinergic blockade conditions (315±43, 384±33 and 390±38 mL/min, respectively), with ICA blood flow always being higher with cholinergic blockade (P<0.05). These findings indicate that the cholinergic contribution to the internal carotid artery blood flow responses to dynamic exercise in humans is minimal.