My Professor asked for an answer to the paradox why when adrenergic blockers suppress the SNS does tachycardia occur.Why do adrenergic blockers motive tachycardia?
Alpha receptors are present on vascular smooth muscle, and control arteriolar and venous tone.
Alpha 1 blockade ----> vasodilation ----> decrease peripheral resistance and BP
Reflex sympathetic control of capacitance vessel is blocked
----> postural hypotension & reflex tachycardia
Alpha2 blockade enhances this reflex tachycardia because the inhibitory effect on norepinephrine release is blocked, and more NE released to stimulate Beta1 receptors surrounded by the heart
Hope that helps.
Monday, September 27, 2010
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