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Alpha-1 adrenergic receptor control of the cerebral vasculature in humans at rest and during exercise

submitted by goremo 1 year and 9 months ago
We tested the hypothesis that pharmacologic blockade of α-1 adrenoreceptor (prazosin), at rest and during steady-state dynamic exercise would impair cerebral autoregulation (CA) and result in cerebral vasodilatation in healthy humans. In ten subjects beat-to-beat mean arterial pressure (MAP) and mean middle cerebral artery blood velocity (MCA V) were determined at rest, and during low (Ex90) and moderate workload (Ex130) on an upright bicycle ergometer without and with prazosin. Plasma noradrenaline concentrations increased significantly from rest to Ex130 during control (from 1.8±0.2 to 3.2±0.3 pmol/ml plasma). In the control condition the transfer function gain between MAP and MCA V in the low frequency (LF) range was decreased at Ex90 (P = 0.035) and Ex130 (P = 0.027) from rest. A significant increase in critical closing pressure (CCP) was also observed in the control condition from rest to Ex90 to Ex130 (from 18±3 to 24±4 to 31±4 mm Hg). An average of 74 ± 2% blockade of blood pressure response was achieved with oral prazosin. Following blockade, plasma noradrenaline concentrations further increased at rest and Ex130 from the control (from 2.6±0.3 to 4.4±0.5 pmol/ml plasma). Prazosin also resulted in an increase in LF gain (P < 0.003) compared to the control condition. Prazosin blockade abolished the increases in CCP during Ex130 and increased the cerebrovascular conductance index (P = 0.018). These data indicate that in the control condition a strengthening of CA occurred with moderate dynamic exercise that is associated with an increase in CCP as a result of the exercise mediated augmentation of sympathetic activity. As α-1 adrenergic receptor blockade attenuated the increase in dynamic CA and CCP, we conclude that increases in sympathetic activity have a role in establishing cerebral vascular tone in humans.


Topic: Biology

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