Why there is no reflex bradycardia when you administer guanethidine?
Guanethidine will prevent the release of NE from the nerve terminal, this will cause a fall in BP. The reflex will attempt to increase the BP by activating the alpha1-receptors to cause vasoconstriction and the beta1-receptors to increase HR. However these actions are prevented by the adrenergic neuron blocking effect of guanethidine (inhibition of NE release). Thus the overall effect with guanethidine is a fall in BP and a slight increase in HR (removal of vagal tone).
