Wednesday, August 15, 2012

Alpha blockade

Whenever we use a non selective alpha blocker, a reflex tachycardia is prominent.

Alpha2 receptors are present prejunctionally on nerve endings which inhibit transmitter release

If you block these receptors, there is an increased release in NA from sympathetic nerves
which causes the tachycardia

What happens if you use a selective alpha1 blocker?

There is a block in sympathetically mediated vasoconstriction and produces a fall in BP which is attended by mild tachycardia; NA release is not increased due to absence of alpha2 blockade