The document discusses vasomotor reversal of Dale and re-reversal of vasomotor reversal. It explains that adrenaline initially causes a biphasic blood pressure response due to its effects on α1 and β2 receptors. Blocking α1 receptors with an alpha blocker causes adrenaline to only decrease blood pressure via β2 receptor activation, known as vasomotor reversal. Re-reversal involves blocking β2 receptors after vasomotor reversal, so adrenaline increases blood pressure solely through α1 receptor activation.

1. vasomotor reversal of dale may be looking difficult, right?
Let us understand it in very easy way.
We should remember following points about receptors:
1. Adrenaline acts on - α1, α2,β1,β2,β3
2. α1, - presents in blood vessels – causes vasoconstrictions- increases blood
pressure
3. β2 – presents in blood vessels- causes vasodilatation – decrease in blood pressure
We should also keep in mind that
1. At lower concentration of adrenaline β2 – receptors are more sensitive
2. At higher concentration adrenaline acts on all receptors
Now to observe effects on blood pressure of adrenaline we have to give adrenaline
intravenous rapidly. (In dog)
1. When we give adrenaline intravenously, initially the concentration of adrenaline is high.
a. So it will act on α1, β2.
b. But actions of α1 (vasoconstriction), will predominate over actions of
β2 (vasodilatation)
c. So there will be rise in blood pressure
2. Within few second level of adrenaline will decrease due to its rapid metabolism and
neuronal re- uptake
a. At lower concentration only action of β2 will predominate
b. So only fall in Blood pressure seen
3. So at this level you can observe initially rise in blood pressure and then after fall in
blood pressure. This is called biphasicresponse (It is not vasomotor reversal of dale)

2. So what is vasomotor reversal of dale?
After biphasic response if we administer non-selective alpha blocker
 It blocks the alpha receptors, hence α1 mediated vasoconstriction
Now, if you give Adrenaline again what will happen?
 Only β2 mediated action occur (why?- because α1 receptors are blocked by
alpha blocker)
 So only fall in blood presser is seen, rather than biphasic response
This phenomenon is called Vasomotor reversal of Dale

3. To understand Re-reversal of vasomotor reversal, We need to understand
Vasomotor reversal of dale.
Please read Vasomotor reversal of dale on below mention link.
http://pharmacologymbbs.blogspot.in/2015/08/vasomotor-reversal-of-dale.html
So As We have seen in Vasomotor reversal-
1. First give adrenaline and observe biphasic response
2. second We give non-selective alpha blocker
3. At last We give adrenaline again and observe only fall in BP due
to unopposed β2 mediated action
This was all about vasomotor reversal of dale.
Now what about Re-reversal? - ( As name suggests re- reversal, We have
to reverse the action which happened in Vasomotor reversal of Dale)
For this
1. First We give adrenaline intravenously and observe biphasic response
2. Now, second step, We give non Selective Beta Blocker (instead of non
selective alpha blocker)
 It blocks the β2 receptors, hence β2 mediated vasodialatation will be blocked
3. Now, if you give Adrenaline again what will happen?
 Only α1 mediated action occur- vasoconstriction - rise in
blood pressure (why? because β2receptors are blocked by beta blocker)
 So only rise in blood presser is seen, rather than biphasic response
This phenomenon is called Re-reversal of Vasomotor reversal of Dale